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Los Angeles St. * MENLO PARK, California--Bldg. 3 (Stop 533), Rm. 3128, 345 Middlefield Rd. * RESTON, Virginia--503 National Center, Rm. 1C402, 12201 Sunrise Valley Dr. * SALT LAKE CITY, Utah--Federal Bldg., Rm. 8105, 125 South State St. * SAN FRANCISCO, California--Customhouse, Rm. 504, 555 Battery St. * SPOKANE, Washington--U.S. Courthouse, Rm. 678, West 920 Riverside Ave.. * ANCHORAGE, Alaska--Rm. 101, 4230 University Dr. * ANCHORAGE, Alaska--Federal Bldg, Rm. E-146, 701 C St. Maps Maps may be purchased over the counter at the U.S. Geologi- cal Survey offices where books are sold (all addresses in above list) and at the following Geological Survey offices: * ROLL A, Missouri--1400 Independence Rd. « DENVER, Colorado--Map Distribution, Bldg. 810, Federal Center * FAIRBANKS, Alaska--New Federal Bldg., 101 Twelfth Ave. Debris Flows from Tributaries of the Colorado River, Grand Canyon National Park, Arizona By ROBERT H. WEBB, PATRICK T. PRINGLE, ard GLENN R. RINK U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1492 Prepared in cooperation with the U.S. Bureau of Reclamation UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1989 DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data Webb, Robert H. Debris flows from tributaries of the Colorado River, Grand Canyon National Park, Arizona / by Robert H. Webb, Patrick T. Pringle, and Glenn R. Rink. p. - cm. -(U.S. Geological Survey professional paper ; 1492) "Prepared in cooperation with the U.S. Bureau of Reclamation." Bibliography: p. Supt. of Docs. no.: I 19.16:1492 1. Mass-wasting-Arizona-Grand Canyon. I. Pringle, Patrick T. II. Rink, Glenn R. III. United States. Bureau of Reclamation. IV. Title. V. Series. QE598.5.U6W43 1989 557.3 s-dc20 89-600091 [551.3'07'09791832] CIP For sale by the Books and Open-File Reports Section, U.S. Geological Survey Federal Center, Box 25425, Denver, CO 80225 CONTENTS *d g 03 g ADStPAGt- = = = -= --- -==- =- IntrOdUucti0A- - - -- --- =-- --- --- -- --- --- --- --- Extent of debris flows in the Grand Canyon --- --- --- Hydraulics of debris flows- - - - -- --- -- --- -=- --- Debris flows in three tributaries of the Colorado River - - - - MethOds- - - -- --== -==- Lava-Chuar Creek drainage - --- --- --- --- --- Stratigraphy- < - - --- -- --- =-=--------- Longitudinal variation in the 1966 debris-flow - - = -= -= --- --- -==- Discharge calculation --- --- --- --- --- -=- Monument Creek drainage --- -- --- Stratigraphy- < - - -- --- --- -=--------- Longitudinal variation in the 1984 debris-flow depOSits - - < -< -==- -- --- 11 oo or or Of to to ho +4 + a & w w co Debris flows in three tributaries of the Colorado River- Continued Monument Creek drainage-Continued Discharge calculations- - - - - - - --- --- --- ~- Sediment volume --- Crystal Creek drainage --- -- -- --- --- -- -=- =- Stratigraphy- < - - --- --- --- Longitudinal variation in the 1966 debris-flow - < < = -= -=- -- --- Discharge calculations- - - - - --- --- --- -- =- Similarities and contrasts among the drainages - - - - - - Fluvial events in other drainages -- --- --- --- --- ~- Factors responsible for debris flows- - - -- --- --- --- Hydrologic effects of debris flows on the Colorado River - - - Summary --- --- --- --- References Cited- - --- --- ILLUSTRATIONS FIGURE 1. go pe m so. fo - o Qi b n Map showing areas of study in Grand Canyon National Park, APIZONA- - - < < -< -- --- --- -- Map showing the Lava-Chuar Creek drainage at mile 65.5 on the Colorado River - - --- --- -- -=---------~- Photographs showing Lava Creek at the confluence with Chuar Creek, 3.8 miles upstream from the Colorado River - -- Graph showing stratigraphy of debris-flow deposits in the Lava-Chuar Creek drainage --- --- -----------~- Photographs showing Lava Creek, 0.2 mile upstream from the confluence with Chuar Creek -- --- --- --- Graph showing particle-size distributions of the debris flow of 1966 in the Lava-Chuar Creek drainage - -- -- --- -- Map showing the Monument Creek drainage at mile 93.5 on the Colorado River --- --- Photographs showing the mouth of Monument Creek -- Graph showing stratigraphy of debris-flow deposits in the Monument Creek drainage - - - --- --- --- -- Graph showing particle-size distributions of the debris flow of 1984 in the Monument Creek drainage- - --- --- --- Plan map and longitudinal profile for indirect-discharge site B in Monument Creek, 0.5 mile upstream from the Colorado RIv@r- - - - --- ==-- --- -- 12. Hypothetical hydrograph of the debris flow of 1984 in Monument Creek as suggested by stratigraphic evidence --- -- 13. Map showing the Crystal Creek drainage at mile 98.2 on the Colorado River = - -- --- --- --- 14. Graph showing stratigraphy of debris-flow deposits in the Crystal Creek drainage --- --- --- --- -- 15. Photographs showing Dragon Creek, 6.2 miles upstream from the Colorado River -- 16. Graph showing particle-size distributions of the debris flow of 1966 in the Crystal Creek drainage --- --- --- --- 17. Photographs showing Crystal Rapid at the mouth of Crystal Creek - - - = = = -= --- --- --- --- 18. Longitudinal profiles for indirect-discharge sites in the Crystal Creek drainage -- --- --- 19. Graphs showing relation of characteristics of rapids and the contributing drainage area of the tributaries --- -- --- 20. Schematic diagram showing geomorphic features of a typical rapid controlled by debris flows on the Colorado River - - - TABLES TABLE 1. Selected tributaries of the Colorado River, Grand Canyon National Park - - - - - - - - --- --- --- --- 2. Indirect-discharge calculation for the debris flow of 1966 on Lava-Chuar Creek, 0.2 mile upstream from the Colorado RIV@R -- --- --- =-- --- 3. Indirect-discharge calculation for the debris flow of 1984 on Monument Creek at Tapeats Alcove, 1.5 miles upstream from the Colorado River --- --- II Page 12 13 14 16 17 19 21 23 24 25 26 27 Page w co 00 -1 O> ho 12 13 14 15 17 18 19 20 22 25 26 Page 30 31 31 IV CONTENTS TABLE 4. Indirect-discharge calculations for the debris flow of 1984 on Monument Creek at site B, 0.5 mile upstream from the Colorado River --- --- --- --- _-_ eRe e__ Ree ___ R- ~~ 5. Indirect-discharge calculation for the debris flow of 1984 on Monument Creek at site C, 0.3 mile upstream from the Colorado River --- - --- --- --- __ _- ee -e cee cee eee e_ e__ ~~ 6. Four scenarios of deposition on the Monument Creek debris fan used to calculate volumes of sediment deposited during the debris flow of 1984 - - -- --- --- --- _-_ _L RRR RRR RRR RR RRR ~~ 7. Indirect-discharge calculation for the debris flow of 1966 on Dragon Creek at site E, 5.0 miles upstream from the Colorado River --- -- --- --- -_- _- _-_ -_- RRR RRR RR RR _- ~~ 8. Indirect-discharge calculation for the debris flow of 1966 on Dragon Creek at site F, 4.8 miles upstream from the Colorado River -- --- --- --- _ _-_ ___ --- eee cece eee ce- -~ ~ 9. Indirect-discharge calculations for the debris flow of 1966 on Crystal Creek at site G, 0.9 mile upstream from the Colorado River -- -- --- --- _._. RRR eR RRR RR RRR _L ~ 10. Comparison of discharges calculated at all superelevation sites by the cross-sectional area at the highest superelevation marks and an average of the upstream and (or) downstream cross-sectional areas -- -- --- --- --- 11. Historic flow events or channel changes in tributaries of the Colorado River in Grand Canyon National Park --- -- -- 12. Relation between difficulty rating for rapids and drainage area of the contributing tributaries for 67 rapids on the Colorado River -- --- --- --- ___ ___. ___ _ _L ___ LLC METRIC CONVERSION FACTORS For readers who prefer to use the metric (International System) units, the conversion factors for the inch-pound units used in this report are listed below: Multiply inch-pound unit By To obtain metric unit inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) square foot (ft?) 0.09294 square meter (m*) cubic foot (ft) 0.2832 cubic meter (m*) foot per second (ft/s) 0.3048 meter per second (m/s) cubic foot per second (ft*/s) 0.02832 cubic meter per second (m/s) mile (mi) 1.609 kilometer (km) square mile (mi*) 2.59 square kilometer (km*) acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m*/yr) pound (Ib) 453.6 gram (g) ton 0.9072 megagram (Mg) Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-A geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Mean Sea Level of 1929." Page 32 32 33 34 34 35 35 36 38 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, GRAND CANYON NATIONAL PARK, ARIZONA By RoseErt H. Wess, Parrick T. Princur, and GiEnn R. Rink ABSTRACT A reconnaissance of 36 tributaries of the Colorado River indicates that debris flows are a major process by which sediment is transported to the Colorado River in Grand Canyon National Park. Debris flows are slurries of sediment and water that have a water content of less than about 40 percent by volume. Debris flows occur frequently in arid and semiarid regions. Slope failures commonly trigger debris flows, which can originate from any rock formation in the Grand Canyon. The largest and most frequent flows originate from the Permian Hermit Shale, the underlying Esplanade Sandstone of the Supai Group, and other forma- tions of the Permian and Pennsylvanian Supai Group. Debris flows also occur in the Cambrian Muay Limestone and underlying Bright Angel Shale and the Quaternary basalts in the western Grand Canyon. Debris-flow frequency and magnitude were studied in detail in the Lava-Chuar Creek drainage at Colorado River mile 65.5; in the Monu- ment Creek drainage at mile 93.5; and in the Crystal Creek drainage at mile 98.2. Debris flows have reached the Colorado River on an average of once every 20 to 30 years in the Lava-Chuar Creek drainage since about 1916. Two debris flows have reached the Colorado River in the last 25 years in Monument Creek. The Crystal Creek drainage has had an average of one debris flow reaching the Colorado River every 50 years, although the debris flow of 1966 has been the only flow that reached the Colorado River since 1900. Debris flows may actually reach the Colorado River more frequently in these drainages because evidence for all debris flows may not have been preserved in the channel-margin stratigraphy. Discharges were estimated for the peak flow of three debris flows that reached the Colorado River. The debris flow of 1966 in the Lava-Chuar Creek drainage had an estimated discharge of 4,000 cubic feet per see- ond. The debris flow of 1984 in the Monument Creek drainage had a discharge estimated between 3,600 and 4,200 cubic feet per second. The debris flow of 1966 in the Crystal Creek drainage had a discharge esti- mated between 9,200 and 14,000 cubic feet per second. Determination of the effective cross-sectional area was a problem in all calculations involving superelevations on bends because areas near superelevation marks were 1.5 to 3.5 times larger than areas of upstream or down- stream cross sections. Debris flows in the Grand Canyon generally are composed of 10 to 40 percent sand by weight and may represent a significant source of beach-building sand along the Colorado River. The particle-size distribu- tions are very poorly sorted and the largest transported boulders were in the Crystal Creek drainage. The large boulders transported into the Colorado River by debris flows create or change hydraulic controls (rapids); these controls appear to be governed by the magnitude and frequency of tributary-flow events and the history of discharges on the Colorado River. Reworking of debris fans by the Colorado River creates debris bars that constrain the size of eddy systems and forms second- ary rapids and riffles below tributary mouths. INTRODUCTION Sediment transported from small drainages is a poten- tially significant contribution to the sediment budget of the Colorado River in Grand Canyon National Park, Arizona (fig. 1). Little is known about the annual sediment yields from these drainages; however, many researchers have noted the efficacy of tributaries for moving large boulders into the Colorado River, which locally form rapids (Dolan and others, 1978; Graf, 1979; Hamblin and Rigby, 1968; Kieffer, 1985; Leopold, 1969). Indeed, large rapids may be the most obvious geomorphic and hydro- logic manifestation of sediment transport from small drainages in Grand Canyon National Park. Estimation of sediment yields from ungaged Colorado River tributaries in Grand Canyon National Park is dif- ficult and uncertainties in cited figures are large. Howard and Dolan (1981) estimated an average annual sediment yield for these tributaries of 2,100 acre-ft/yr by use of a sediment-mass balance for the Colorado River. However, they estimated the change in storage of sediment in the bed of the Colorado River by using an average channel width and by assuming that sand covered an average of 75 percent of the channel bed. Laursen and others (1976) estimated an average annual sediment yield of 0.7 acre- ft/yr of "beach-building sand" on the basis of differences in suspended-sediment transport between the gaging stations at the Colorado River at Lees Ferry and the Colorado River at Grand Canyon. Mass-balance estimates of sediment yields contain considerable uncertainty because the change in bed storage is unknown. Sediment yields from these tributaries also could be estimated using methodology presented by the Pacific Southwest Inter-Agency Committee (1968). This method- ology was developed from rangeland monitoring efforts on terrain with low to moderate topographic relief. Sedi- ment yields are determined from a quasi-analytical procedure that is based on geology, soils, climate, drainage-basin characteristics, and channel stability. Use of the methodology requires the tacit assumption that sediment is transported by Newtonian streamflow. The 2A DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA method produces a sediment yield per unit area, which implies that drainage-basin area is the most important fac- tor influencing sediment yield. In the study of the tributaries of the Colorado River, the key to estimating sediment yield is an understanding of the sediment-transport process. A previous flood report (Cooley and others, 1977) and recent mapping of alluvial deposits in tributary canyons during this project indicate that debris flow is the dominant process for sediment transport in small drainages in Grand Canyon National Park. Debris flows are common in arid and semiarid drainages (Blackwelder, 1928); however, their importance in supplying sediment to the Colorado River has not been previously recognized. The purpose of this report is to document the extent of debris flows in Grand Canyon National Park and the occurrence and magnitude of debris flows in three Colo- rado River tributaries. The effects of these events on the mainstem-channel morphology are necessary in under- standing sediment transport and hydraulic controls in the Colorado River. This study was funded in cooperation with the U.S. Bureau of Reclamation as part of a larger study entitled "Glen Canyon Environmental Studies." ACKNOWLEDGMENTS The authors thank J.T. Brown, M.D. Daggett III, S.L. Reneau, and V. A. Yocum for their help with the fieldwork and companionship during the river trip. R.M. Turner of the U.S. Geological Survey rephotographed historic scenes in Monument, Crystal, and Dragon Creeks. R.C. Euler of the National Park Service shared his Grand Canyon archaeological experiences and provided photo- graphs of the Crystal Creek and Lava-Chuar Creek drainages. Hal G. Stevens, formerly of the U.S. Geological Survey, generously provided his matched photograph of Hillers' view of the mouth of Monument Creek. V.A.S. McCord and TP. Harlan of the Laboratory of Tree-Ring Research, University of Arizona, examined tree-ring specimens that exhibited damage from debris flows. J.D. Rogers, Rogers/Pacific Consultants, Lafayette, Califor- nia, provided published and unpublished manuscripts on debris flows and geology of the Grand Canyon. Bryan Brown, Kim Crumbo, Larry Stevens, and Mike Yard, Colorado River boatmen, shared their experiences with Grand Canyon navigation and changes in rapids. Mike Walker and Mike Yard provided eyewitness accounts of < GP EXPLANATION f . River miles o & Study area ARIZONA INDEX MAP | & f Grand Canyon | National Park - C | Va meod Boundary\ | Lava L Saa | -* x) Falls ~- ~A role | & Rapid R L &_ [ja - (200) 6 ol. j ~ 4 & se®k- J C| $ ‘ 3 (250) « $ - (I‘m Pond Peach Springs | N T A H hs fl, T L] o [om tf moO s.. Loke Ea "/o Powell & o. c & 3, - f hose G Lees Ferry)® (0) 8 & y A % A A # Q3 Roaring , CRYSTAL Twenties CREEK | | a DRAINAGE © [f ___ (see tig. 13) i f 50 ieee a N C $& SC LAVA-CHUAR CREEK C § 6 DRAINAGE (see fig. 2) e C y b¥ __ $& yo 5 a *% Ne C“ W ‘ all Fi had % z % ~. ;\\} o ‘ \_ . Grand | o MONUMENT 1 Canyon _ / ;% -- ' CREEK * Red &, DRAINAGE Canyon do &, (see fig. 7) Hance . Ropid 0 25 MILES 0 25 KILOMETERS FIGURE 1.-Areas of study in Grand Canyon National Park, Arizona. HYDRAULICS OF DEBRIS FLOWS 3 Grand Canyon debris flows. S.W. Kieffer and T.C. Pier- son of the U.S. Geological Survey and S.L. Reneau of the University of California at Berkeley critically reviewed the manuscript. Jack C. Schmidt and Julia B. Graf, U.S. Geological Survey, Tucson, discussed aspects of the research and provided a different perspective on the hydrologic effects of debris flows on the Colorado River. We especially thank Curt Green, Bob Marley, and Tom Wise of the U.S. Geological Survey for being excellent field assistants and skeptics; we hope to share more field seasons with them. EXTENT OF DEBRIS FLOWS IN THE GRAND CANYON Debris flows are flowing water-based slurries of poor- ly sorted clay- to boulder-sized particles (Costa, 1984). Terms sometimes intended to be synonymous include mudflows, debris slides, debris torrents, mud slides, or lahars (volcanic debris flows). Debris flows occur in many different environments ranging from deserts (Johnson and Rodine, 1984) to montane forests (Gallino and Pier- son, 1985) and offshore continental shelf slopes (Piper and others, 1985). Debris flows tend to form their own chan- nels between levees that are parallel to the flow direction when unconfined by an existing channel. These levees are composed of boulders which commonly appear to be floating in a matrix of gravel, sand, and clay (Costa, 1984; Johnson and Rodine, 1984) and have a distinctly different morphology from typical alluvial deposits. Many classification schemes have been proposed for coarse-grained sediment flows based on water content during transport (Beverage and Culbertson, 1964), char- acteristics of the resultant alluvial deposits (Smith, 1986; Pierson and Scott, 1985), or on assumed rheological models of flow dynamics (Postma, 1986). Debris flows typically have 15 to 40 percent volumetric water content compared with 40 to 80 percent for hyperconcentrated flows and 80 to 100 percent water for streamflows (Beverage and Culbertson, 1964). The main distinction in this study is the difference between debris-flow deposits and hyperconcentrated-flow deposits (Beverage and Culbertson, 1964; Scott, in press) because debris flows can transform into hyperconcentrated flow with distance from the source area (Pierson and Scott, 1985). This distinc- tion is important because hyperconcentrated flows are quasi-Newtonian fluids and debris flows are not. Debris-flow deposits are differentiated from hypercon- centrated-flow deposits on the basis of characteristic particle sorting, sedimentary structures, and inferred rheological properties. Readers are referred to detailed descriptions of each type of deposit in Smith (1986) and Scott (1985). Debris-flow deposits are characterized by lack of sedimentary structures, poor sorting of particles, matrix support of cobbles and boulders, and, in some cases, inverse fine to coarse grading. Hyperconcentrated- flow deposits are also poorly sorted but exhibit clast sup- port of large particles, have weak sedimentary structures, and cannot transport the extremely large boulders moved during debris flows. Streamflow deposits are well-sorted, have imbricated clasts and well-developed sedimentary structures, and are easily distinguished from debris-flow deposits. We studied 36 tributaries of the Colorado River, and all had characteristic debris-flow deposits (table 1). Most tributaries have only debris-flow deposits and inconspicu- ous hyperconcentrated-flow deposits; a few tributaries in the western Grand Canyon (such as Havasu Creek, fig. 1) have both well-sorted streamflow deposits and debris- flow deposits. Twenty-one of the 36 tributaries have evidence of debris flows within the last 25 years, including fresh boulder levees and matrix-supported deposits. This sampling of the nearly 310 ungaged tributaries of the Colorado River between Lees Ferry and Diamond Creek (fig. 1) suggests that debris flows are a major process of sediment transport from small drainages to the Colorado River in Grand Canyon National Park. HYDRAULICS OF DEBRIS FLOWS Debris flows have properties important both to hydrau- lic calculations and preservation of evidence for past events. Debris flows are non-Newtonian, or cohesive fluids that commonly move essentially as a plug in high-velocity laminar flow (Enos, 1977; Johnson and Rodine, 1984). Viscosities for debris flows may be several orders of magnitude higher than the viscosity of water (Costa, 1984). Particle interlocking in the dense fluid results in internal friction and shear strength. As a result, debris flows have a finite thickness called the critical thickness at a velocity of zero. Turbulence is dampened in the mov- ing fluid (Enos, 1977), which results in laminar flows that have significantly higher Reynolds numbers than in streamflows (Costa, 1984; Johnson and Rodine, 1984). These properties enable debris flows to be extremely erosive in channels and yet to flow around brittle plants on nearby channel margins. As a result, evidence for past debris flows was found entrained in the spines of live cacti, whereas 2-ft diameter cottonwoods were sheared off on nearby flood plains in Colorado River tributaries that have had recent debris flows. One facet of debris-flow hydraulics facilitates the crea- tion and maintenance of Colorado River rapids. Debris flows can transport large boulders long distances from source areas. This property may result from cohesive strength, which is largely a function of clay content; from buoyancy forces on large particles that increase because of lessened density differences with the surrounding debris-flow matrix; from greater shear stress and high drag forces at the base of the debris flow; from slightly 4 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA positive pore-water pressures in debris flows; or from a combination of these factors (Costa, 1984; Johnson and Rodine, 1984; Pierson, 1981). Regardless of the process, the characteristic boulder fans at the mouths of Colorado River tributaries (Hamblin and Rigby, 1968; Howard and Dolan, 1981; Stevens, 1983) result from debris-flow deposition and subsequent reworking of the deposits to remove the matrix. The hydraulics of debris flows are unusual compared with streamflow because of the high sediment concentra- tions and interactions among particles. Most indirect velocity calculations for streamflow use Manning's equation y -_L42 . post . go.5 o M where v= mean velocity, R= hydraulic radius, S= the fric- tion slope, and »=the roughness coefficient. Equation 1 cannot be applied to debris flows because the roughness coefficient cannot be accurately estimated (Antonious Laenen, U.S. Geological Survey, written commun., 1986; Laenen and others, 1987) and because debris flows are not Newtonian fluids. Application of the Manning equa- tion using the slope-area method (Chow, 1959) resulted in a substantial overestimation of discharge for debris flows in Colorado (Costa and Jarrett, 1981). Debris flows have been modeled as a Bingham sub- stance (Johnson and Rodine, 1984) and as a viscoplastic fluid (Chen, 1985). Use of either method for calculating velocities of debris flows requires estimation of coeffi- cients related to shear strength or flow behavior. These coefficients have large ranges and considerable error is involved in their estimation. For example, A. Laenen (written commun., 1986) has shown that Chen's (1985) flow-behavior index, back-calculated from measured debris flows, varied by an order of magnitude during a single event and varied by more than three orders of magnitude when different events were compared. Such variation indicates that calculation of velocities from post- event evidence using these methods would involve con- siderable potential error. For this study, we used simplified hydraulic formulae to calculate flow velocities for debris flows (Pierson, 1985). Evidence for the elevation of the velocity head (Chow, 1959) usually is found where an obstacle is oriented perpendicular to the flow direction. In the Grand Canyon, flow impinging on vertical bedrock walls generally will leave runup evidence in sites that are protected from weathering. The mean velocity, v, is calculated by equat- ing the kinetic energy of the flow to the potential energy of the runup by v =(2 : g : Ah, )95 (2) where g=gravitational acceleration (82.2 ft/s) and An, = the difference between the runup and unobstructed flow- surface elevations. An energy-correction coefficient normally applied to open-channel hydraulics is assumed to be 1 because of plug flow. Energy losses are assumed to be negligible. Superelevation occurs on bends as a result of centrifu- gal-acceleration forces. The water-surface profile on the inside and outside of a bend drops and rises, respective- ly, to form an elevation difference An, (Pierson, 1985, fig. 4). Assuming that all streamlines follow the same radius of curvature (assumed to be the centerline radius of cur- vature, R,,), fully developed plug flow, and negligible energy losses, the mean velocity around a bend is calcu- lated from v =(g -R, Ahs/k - W)5 (3) where W=the effective channel width and k=a correc- tion factor (Hungr and others, 1984). Hungr and others (1984) suggest that k= 2.5 to correct for reported over- estimation of debris-flow velocities; however, we used k=1 because equations 2 and 3 then provided internally consistent velocities. More sophisticated equations for calculating velocity from superelevation (Apmann, 1973) probably are not warranted for debris flows in irregular natural channels. Application of equations 2 and 3 to debris flows has been widely used but the results have been uncertain. Pierson (1985) found that use of these formulae resulted in com- puted velocities averaging 15 percent lower than actual velocities on the basis of measured travel times. Hence, use of equations 2 and 3 may result in a slightly conser- vative estimate of velocity. The amount of error intro- duced by the other assumptions is unknown but probably is high. The resultant discharge Q is estimated from Q =A < v (4) where A = cross-sectional area. Use of equation 4 requires the assumption that all of the fluid passing through cross- sectional area A is moving at a mean velocity of v. This assumption may not be valid because of ineffective flow areas on bends (see section "Similarities and Contrasts Among the Drainages"). Froude numbers were calculated from 2 =- (5) where D is the hydraulic depth (A/W). In Newtonian streamflow, Froude numbers greater than 1 indicate supercritical flow while Froude numbers less than 1 in- LAVA-CHUAR CREEK DRAINAGE 5 dicate subcritical flow. It is uncertain whether Froude numbers have the same significance when applied to debris flows. Enos (1977) found no consistent quantitative measure to define different energy regimes in debris flows. DEBRIS FLOWS IN THREE TRIBUTARIES OF THE COLORADO RIVER The magnitude and frequency of debris flows were evaluated in three Colorado River tributaries (fig. 1). Lava-Chuar Creek drainage at mile 65.5 on the Colorado River had a debris flow during a storm on December 3-6, 1966 (Cooley and others, 1977). Monument Creek at mile 93.5 had a debris flow during a summer thunderstorm on July 25, 1984 (Potochnik and Reynolds, 1986). The Crystal Creek drainage at mile 98.2 also had a debris flow during the storm in December 1966 (Cooley and others, 1977). Peak discharges for these three events were estimated, and the channel-margin stratigraphy was analyzed for other past events. The fieldwork for this project was com- pleted in March and April 1986. METHODS The stratigraphy in the drainages that were investi- gated was described to provide a chronology of debris flows. Correlations among deposits were made on the basis of characteristic lithologies, sedimentary structures, color, stratigraphic position, and degree of particle-size sorting. Organic samples contemporaneous with past debris flows were collected for radiocarbon analysis by accelerator-dating techniques (Taylor and others, 1984) or conventional gas-proportional counting. Accelerator dating was used for some samples because they were too small to be analyzed by conventional gas-proportional counting. Analyses of scarred trees (Hupp, 1984), historical photographs, aerial photographs, and damage to historic structures provided additional dating of events. The deposits from the debris flow of 1966 were iden- tified from photographs in Cooley and others (1977) and by observation of damaged trees and recent deposits in the Lava-Chuar Creek and Crystal Creek drainages. Deposits from the 1984 debris flow in Monument Creek were fresh and easily identified. Deposits were traced longitudinally using stratigraphic and sedimentologic characteristics. High-water marks were preserved as lines under small rock overhangs; as mud deposits in and under cacti, trees, and shrubs; as distinct levees or overbank deposits; and as distinct mud lines deposited over older material on hillslopes. The red color of the debris-flow deposits in Crystal Creek, for example, was vivid when emplaced against the dark brown soils on hillslopes or as a mud line against the reddish brown Cambrian Tapeats Sandstone. We collected 5- to 10-pound samples of debris-flow matrix (diameter less than 16 mm) for reconstitution of water content during the event (Cooley and others, 1977; Gallino and Pierson, 1985; Johnson and Rodine, 1984). Water was gradually added to the samples until the mix- ture had observable cohesion and matrix support of 16-millimeter particles. This method is relatively precise because small changes in the water content cause large changes in cohesion (Costa, 1984). In the samples, a 1 to 2 percent by weight (2 to 4 percent by volume) range in water contents that created a debris-flow type of fluid was measured. Additional uncertainty occurs from changes in the particle size of deposits during post-event dewater- ing (Gallino and Pierson, 1985) or by lateral or longitudinal facies changes. This uncertainty was minimized by selec- tive sampling of intact debris-flow matrix in protected sites and near sites where discharges were estimated. Samples were sieved to obtain particle-size distributions by weight percent, and point counts of particle diameters were made in the field. The two methods yield a numer- ically equivalent particle-size distribution (Kellerhals and Bray, 1971; Pierson, 1980). LAVA-CHUAR CREEK DRAINAGE The Lava-Chuar Creek drainage, 21.3 mi? in area, heads on the Walhalla Plateau in the eastern Grand Can- yon (figs. 1, 2). The bedrock geology of this drainage con- sists of an entire Paleozoic section of rocks (McKee, 1969) that form cliffs in the headwaters, Precambrian Galeros Formation that underlies more than 75 percent of the drainage in the open Chuar Valley, and Precambrian Dox Sandstone that is exposed in the first mile above the con- fluence with the Colorado River (Huntoon and others, 1986). The topographic relief in the drainage basin is 5,300 ft and the average channel slope is 0.1. A debris flow occurred in the drainage as a result of intense rainfall in December 1966. An estimated 12 to 14 in. of precipitation fell during the 5-day storm (Cooley and others, 1977). A debris flow began with multiple slope failures in the Permian Hermit Shale and Esplanade Sandstone in Natchi Canyon (fig. 2) and continued 6.5 mi to the Colorado River. Additional slope failures from the same formations in Lava Canyon (fig. 2) may have con- tributed sediments to the debris flow. Cooley and others (1977) report considerable damage throughout the canyon from the debris flow but do not report a discharge for the event. R.C. Euler (National Park Service, oral commun, 1986) visited archaeological sites in the canyon before and after the debris flow, and his photographs illustrate the extent of channel changes (fig. 34, B). It is not certain to what extent Lava Canyon Rapid at the mouth of the Lava-Chuar Creek drainage on the Colorado River was affected by this debris flow. 6 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA STRATIGRAPHY In addition to the debris flow of 1966, at least two debris flows have occurred historically in the Lava-Chuar Creek drainage. Exposures of debris-flow sediments deposited before and after 1966 were present at intervals along the entire length of the Lava-Chuar Creek drainage (fig. 4). Replication of photographs presented in Cooley and others (1977) indicates that a debris flow occurred after 1966 (fig. 5). A comparison of aerial photographs indicated that this flow occurred between 1973 and 1984. The peak stage for the post-1966 debris flow was lower than the 1966 debris flow near the confluence of Lava and Chuar Creeks (site C, fig. 2) but was about equivalent near the mouth. The relation of discharge to stage is unknown because the post-1966 debris flow or other unknown streamflows local- ly entrenched the bed of Lava Creek by 2 to 5 ft over a 10- to 15-foot width from the level of 1966 (fig. 5). In the 1-mile reach above the Colorado River, the presence of substantial material from the Dox and Galeros Formations in post-1966 debris-flow deposits indicates significant local sediment contributions from small side drainages, scour of channel deposits, and (or) slope failures. An older and substantially larger debris flow occurred in Lava Creek in historic times before 1966. Cooley and others (1977) report the presence of driftwood deposited before 1966 near the confluence with Chuar Creek; similar driftwood mixed with boulders in a debris-flow levee was found at higher elevations above the channel than reported by Cooley and others (1977). The older debris flow overtopped an abandoned grinding mill at Mac- Donald Spring (site D, fig. 2) that was probably con- structed as part of a distilling operation between 1890 and 1915 (Harvey Butchart, retired professor, Northern 11°55" 11°50" I ..'\. * \ I Goo ) * > ,. A o I MILE +* ** *» se®is'|- 7 A ** mt 0 | KILOMETER « "a /] s NR CONTOUR INTERVAL 2000 FEET ‘ \ /I ( \ /} 600, NATIONAL GEODETIC VERTICAL a | A R 1 DATUM oF 1929 2 i A\ * Miu, \ ® Fr 3 e * { (é f 0 ig \. {a j . A \— a. \ D90 , . . al +C 7 " . ; \ + - x - T \. - " Drainage E / \ 32???“ ( \ .)/: boundary m * ..<:1 -. " T> :\ ev l _Natchi Canyon me, k- _ B C '\ o e e i /‘ | J Do. S a EE ( q \.. C \ .* \"V'. & F ge ‘0'\ k? { j Juno \ \ E 5 \ & Temple 36°08" |- ® EXPLANATION mer PEth Of CQDFS flOW X Slope failure, December 1966 A Slope failures starting the debris flow B Depositional area C Photo replication site (see figures 3, 5) D MacDonald Spring E Depositional splays F Indirect - discharge site | «*[(L ava Canyon Rapid FIGURE 2.-The Lava-Chuar Creek drainage at mile 65.5 on the Colorado River. See figure 1 for location. LAVA-CHUAR CREEK DRAINAGE T Arizona University, oral commun., 1986). The debris flow deposited distinctive sediments in the mill and left the trunk of an uprooted cottonwood tree on the nearby terrace. This flow also lapped onto a 10-foot-high terrace near the confluence with the Colorado River and nearly damaged an historic housepad. The pre-1966 debris flow deposited sediments twice as thick as the preserved sediments of the debris flow of 1966 in some places along the channel (fig. 4). Evidence for at least five prehistoric debris flows is preserved in prominent terraces along Lava Creek (fig. 4). Hyperconcentrated-flow deposits and possible channel- fill facies of additional debris flows also were found. Sediments are preserved as much as 12 ft above the chan- nel bed of 1986 near the Colorado River and as much as 20 ft above the channel bed in the narrow reaches near the headwaters. Driftwood lodged in a debris-flow deposit (symbol Z; fig. 4) 12 ft above the channel bed of 1986 had a radiocarbon age of 250 +80 yr B.P. (years before pres- ent) (sample number A-4543). This deposit could not be traced downstream from site B (fig. 2). Radiocarbon dating of entrained wood in debris-flow deposits X and W (fig. 4) indicate maximum ages of 625 +65 (A A-1787) and 1,460 +60 (AA-1788) yr B.P. for these debris flows, respectively. The younger of these events (X) had a hyperconcentrated-flow facies associated with the deposit. On the basis of deposit thickness and height above the channel, the debris flows W, X, and Y had little attenua- tion in stage in the 3-mile reach between sites E and F (fig. 2) and reached the Colorado River. FIGURE 3.-Lava Creek at the confluence with Chuar Creek, 3.8 miles upstream from the Colorado River. View B (May 1967) is slightly dif- ferent from A (May 1966) and shows significant channel alteration following the 1966 debris flow. View C (March 1986) matches B and shows revegetation and entrenchment of the channel after the 1966 and subsequent debris flows. Photograph by R.C. Euler (National Park Service). See site C, figure 2, for location. 8 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA The stratigraphy in the Lava-Chuar Creek drainage suggests an average interval of about 20 to 30 years between debris flows during the last 80 years, depending on the age used for the mill at MacDonald Spring. On the basis of radiocarbon-dated debris-flow deposits in ter- races, the Lava-Chuar Creek drainage has had a minimum of one debris flow that reached the Colorado River every 190 years during the last 1,500 years. Debris flows may actually reach the Colorado River more frequently because small prehistoric debris flows, such as debris flow Z, may not have overtopped the terraces to leave deposi- tional evidence. LONGITUDINAL VARIATION IN THE 1966 DEBRIS-FLOW DEPOSITS Sedimentologic characteristics of the debris flow of 1966 show little significant longitudinal variation in cohesive- ness. As noted by Cooley and others (1977), the flow re- mained a debris flow the entire length of the drainage. The flow sustained or locally increased its volume by incorporation of bed material, talus, and exposed sedimen- tary rocks of the Galeros and Dox Formations. Abundant vesicles preserved in the debris-flow matrix at many sites indicate significant air entrapment in the flow or frothy, HEIGHT OF DEPOSITS, IN FEET 6254+65 1460+60 DISTANCE UPSTREAM FROM THE COLORADO RIVER,!N MILES o L . 0.2 1.9 29 3.1 3.8 4.0 Channel bed EXPLANATION Radiocarbon age, in years before present Post - 1966 debris-flow deposit 1966 debris-flow deposit Historic debris-flow deposit Prehistoric debris-flow deposit Soil or incipient soil Stratigraphy hidden or not present Talus, hillslope debris, or Colorado River deposit Boulder Labels for correlative debirs-flow deposits ro J 0 t ® o »BNGCESN = x ~ n FIGURE 4.-Stratigraphy of debris-flow deposits in the Lava-Chuar Creek drainage. turbulent conditions at the flow margins. Mudcoats pre- served on bedrock walls and indurated calcic deposits also demonstrate that the flow retained its cohesive proper- ties throughout the length of the drainage. Upon debouching from Natchi Canyon, the debris flow deposited an extensive field of boulders over what previously was a marshy site (Cooley and others, 1977). The 1966 levee is 6 ft above the channel bed of 1986 downstream of Natchi Canyon, whereas the debris-flow deposit Z and associated driftwood is 12 ft above the chan- nel. Between sites B and C (fig. 2), the debris flow was confined in a narrow, boulder-clogged channel with a steplike appearance (Cooley and others, 1977, fig. 29B). FIGURE 5.-Lava Creek, 0.2 mile upstream from the confluence with Chuar Creek. View A (March 1967) shows that the debris flow of 1966 has created a nearly level denuded channel. View B (March 1986) shows an entrenched channel and post-1966 debris-flow deposits in the foreground. See site C, figure 2, for location. MONUMENT CREEK DRAINAGE o Little depositional evidence for the 1966 debris flow is preserved in this reach, and deep scour holes suggest this to be a reach of many transformations between laminar and turbulent flow (Fisher, 1983) and predominantly supercritical flow conditions. The reach immediately above MacDonald Spring (site D, fig. 2) is similar. At site E, the debris flow was not confined by lateral terraces for 0.2 mi. A large levee formed and was repeatedly breached as the flow deposited lobate splays of sediment. The critical thickness of the deposit at which the debris flow stopped moving ranged from 1.6 to 2.3 ft, and boulders 2 to 5 ft in diameter compose the pre- served levee. The volume of sediment preserved in the lobes suggests that this debris flow was sustained for a relatively long time period rather than consisting of a single, short pulse behind a moving boulder dam. The debris flow of 1966 inundated a 6-foot-high terrace 800 ft upstream from the Colorado River and deposited sediments 0.1 to 1.3 ft thick composed of poorly sorted particles and matrix-supported boulders. Particle-size distributions for the debris flow of 1966 indicate a poorly sorted and coarse-grained deposit (fig. 6). The debris flow had 4 to 5 percent silt and clay and about 30 to 35 percent sand. One boulder at site F (fig. 2) that was transported during the debris flow of 1966 had a median diameter of 4.8 ft and weighed an estimated 9 tons. More commonly observed boulders were 1 to 2 ft in diameter. Reconstitution of debris-flow deposits from the Lava-Chuar Creek drainage indicated a water content of 21 to 24 percent by volume. DISCHARGE CALCULATION Superelevation evidence deposited from the passage of the debris flow of 1966 around a 90° bend was surveyed PARTICLE DIAMETER,IN @ UNITS -8 -4 0 4 8 ._ -E Z u - - te u; - 80f 4 a. 2 | Debris-flow deposit { -_ 60} at site F | X 2 - ugJ 40} Debris-flow deposit | id at site C 2 F { f— < 20} - 3 > { : O 1 i 1 i a L ___4_ T & 256 16 1 0.063 - 0.004 PARTICLE DIAMETER , IN MILLIMETERS FicurE 6.-Particle-size distributions of the debris flow of 1966 in the Lava-Chuar Creek drainage. See figure 2 for locations of sites. 0.2 mi upstream from the Colorado River (site F, fig. 2). The 12-foot-thick debris-flow deposit was preserved against a near-vertical cliff of Dox Formation. The radius of curvature of the centerline of the channel is 37 ft, whereas the channel width is 110 ft. This apparent discrepancy results from the combination of a bend with a low radius of curvature and a width that includes flow over the point bar on the inside of the bend, and may in- validate the assumption that all streamlines follow the same radius of curvature (see section "Hydraulics of Debris Flows"). A velocity of 12 ft/s was estimated on the basis of an elevation difference (Ah,) of 18.3 ft be- tween the inside and outside high-water marks on the bend (table 2). The velocity could range from 10 to 14 ft/s because of uncertainties in the radius of curvature (R,). Determination of the cross-sectional area of flow was unexpectedly difficult. The cross-sectional area at the superelevation site was about 3.5 times larger than upstream or downstream cross sections. The discharge calculated using the area at the superelevation site is 14,200 ft3/s. If this discharge is correct, use of equation (4) suggests that the velocity must increase downstream to 46 ft/s over 250 ft. Similarly, the flow would have to decelerate from 41 to 12 ft/s over 125 ft as the flow enters the bend. The problem with large cross-sectional areas at superelevation sites compared with upstream and downstream cross sections occurred in the other two tributaries studied, and a justification for the discharge calculations is presented in the section "Similarities and Contrasts Among the Drainages." The discharge for the 1966 debris flow was estimated from an average of the cross sections 125 ft upstream and 250 ft downstream, respectively, from the site of max- imum superelevation. Using an average area of 330 ft, the debris flow of 1966 had a peak discharge of 4,000 ft3/s (table 2) with a Froude number between 1.0 to 1.4. The average water content of reconstituted samples is 22.5 percent, hence the peak sediment and water discharges are estimated to be 3,100 and 900 ft9/s, respectively. MONUMENT CREEK DRAINAGE Monument Creek, 3.3 mi? in area, heads on the Coco- nino Plateau on the south side of the Colorado River (figs. 1, 7). The bedrock geology of this drainage consists of the entire Paleozoic section (Huntoon and others, 1986), with the Permian Kaibab Limestone and Coconino Sandstone, Mississippian Redwall Limestone, and Cambrian Muay Limestone forming prominent cliffs. The Permian Her- mit Shale and Permian and Pennsylvanian Supai Group form benches in the otherwise vertical cliffs. An erosional surface in the Cambrian Bright Angel Shale and underly- ing Tapeats Sandstone forms the Tonto Platform, which 10 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA is present in much of the Grand Canyon. Monument Creek cuts through the Precambrian Vishnu Schist in the 1.5 mi upstream from the Colorado River and forms a deep, narrow canyon. Topographic relief in the drainage basin is 4,500 ft and the average channel slope is 0.2. On July 27, 1984, a thunderstorm centered over the eastern part of Monument Creek initiated a debris flow. Rainfall recorded at Grand Canyon, about 1 mi from the headwaters (fig. 1), indicates a total of 1.08 in. for the storm, with 0.92 in. falling in 1 hour. These rainfall totals are not unusual for the station and the month of July 1984 was not unusually wet. However, the high-intensity rain- fall triggered a free-falling avalanche, which fell 2,000 ft into the canyon from the Esplanade Sandstone on the Mo- jave Wall (fig. 7). The coarse, poorly sorted, and angular debris filled the channel to a depth of 20 ft and created a debris dam that had not been breached by 1986. The avalanche transformed into a debris flow with the addi- tion of runoff and water in the channel. Other eastern tributaries of Monument Creek also had debris flows in- itiated by smaller slope failures in the Supai Group (fig. 12°15" u2°i0' I I Granite E Ropid Colorado M f..______ zy & R-___-_- / / D 6 Y i o 1/2 MILE 36°07 |- * - " GOL t- (7 h o 0.5 kILOMETER : ‘ CONTOUR INTERVAL 2000 FEET / \ NATIONAL GEODETIC VERTICAL K DATUM OF 1929 F Drainage boundary 36°02 [-- EXPLANATION =---* Path of debris flow X Slope failure, July 1984 A Tapeats alcove B,C _ Indirect-discharge site D New debris fan E Debris bar ("Island") . t-, wat -_ .> COCONINO PLATEAU _| FIGURE 7.-Monument Creek drainage at mile 93.5 on the Colorado River. See figure 1 for location. 7). The resulting debris flow traveled 2.8 mi to the Colo- rado River, where deposition caused a significant constric- tion of the Colorado River at Granite Rapid (fig. 8). STRATIGRAPHY Deposits preserved in terraces and associated scarred catclaw trees indicate that a historic debris flow occurred before 1984 (fig. 9). Ring counts on scarred and healed catclaw trees suggest that this debris flow occurred 20 to 25 years before 1986. The heights of the searred trees are roughly equivalent to or slightly higher than the stage of the debris-flow peak of 1984. Aerial photographs, however, do not reveal obvious channel changes in Monu- ment Creek after 1965. The pre-1984 debris flow was ini- tiated near or upsteam from the avalanche source for the 1984 debris flow. Locally, this flow deposited 3-foot-thick sediments and had a stage 28 ft above the channel. Evidence for older debris flows in Monument Creek is scanty because of poor exposures and erosion during the FIGURE 8.-Mouth of Monument Creek. In view A (September 1872), the discharge in the Colorado River apparently is between 20,000 and 25,000 cubic feet per second. Curved lines in the center of the photograph are cracks in the original glass-plate negatives. In view MONUMENT CREEK DRAINAGE 11 historic events. Monument Creek has two terraces com- posed of layered debris-flow deposits-a low terrace that was inundated in 1984 and a high terrace covered with mesquite and catclaw trees that was not inundated in 1984. At Tapeats Alcove (site A, fig. 7), an exposure of the high terrace showed three prehistoric debris-flow deposits, one of which had a radiocarbon age of 170 +90 yr B.P. (A-4542). Lack of longitudinal correlation of these deposits with others along Monument Creek, however, precludes any meaningful discussion of the frequency of prehistoric debris flows. LONGITUDINAL VARIATION IN THE 1984 DEBRIS-FLOW DEPOSITS The debris flow of 1984 was initiated at slope failures on the east side of the drainage (fig. 7). The largest slope failure, an avalanche, hit a water-filled channel and splat- tered mud and debris as much as 200 ft above the chan- nel on the west side of the drainage. The particle-size B (September 1968), the discharge in the Colorado River is about 8,000 cubic feet per second. The river appears to be more constricted than in 1872 despite differences in discharge, and a debris flow that oc- curred 2 to 7 years prior to the photograph date may have contributed distribution near the slide (fig. 10B) shows that the flow was poorly sorted with coarse clasts as much as 256 mm in diameter. A lithological count of clasts revealed that 64 percent were sandstones from the Supai Group and 36 percent were from the Redwall Limestone. Downstream from the avalanche, the debris flow may have undergone several transformations from laminar to turbulent flow before reaching Tapeats Alcove (site A, fig. 7). Lodged boulders created local 3- to 10-foot drops in the channel bed; recessional deposits upstream from these drops are clearly of debris-flow origin, whereas hyper- concentrated flow deposits occur downstream from the drops. A particle-size distribution measured above Tapeats Alcove (fig. 10B) shows a poorly sorted debris- flow matrix with 40 percent sand. Two small tributaries of Monument Creek downstream from the avalanche contributed debris flows to the main channel. A debris flow from the downstream tributary oc- curred after the peak, as inferred from a superelevation of the flow over the 7- to 10-foot-high banks of Monument to the constriction. In view C (April 1986), the discharge in the Colorado River is 28,500 cubic feet per second. The 1984 debris flow has constricted the river significantly, especially in comparison with 1872 conditions. 12 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA Creek at the confluence. The flow remained overbank 230 ft downstream and may have caused a recessional debris- flow pulse. No debris from these two tributaries remains in the channel of Monument Creek, indicating that flow in the main channel was still erosive enough to remove the additional sediments. The peak of the debris flow sustained its cohesive prop- erties until it reached the Colorado River. Superelevation marks appear on most bends, and lateral levees were deposited in channel irregularities. In the narrow bedrock canyon 0.25 mi downstream from Tapeats Alcove, three deposits with a lower stage than the peak discharge are preserved. These deposits are suggestive of recessional debris and (or) hyperconcentrated flows following the main pulse. The particle-size distribution for the debris flow in this section (fig. 10C) indicates an increased percentage of boulders and a sand content of 30 percent. The additional boulders were probably entrained from the bed and terraces. Below site B, one boulder transported by the flow is 9 ft in diameter; a second rectangular block 25( za a Ak, ”74, h 20 5d P /e /2/M zz 4??qu,”’ M LZ 170#90 i/ 1B TG, J P6P &* 1984 Levee I / 22 HEIGHT OF DEPOSITS, IN FEET < & 1984 Levee . HINT %// I/1/}z//;' {71/ A ZZ / 0.0 1.1 1.2 L6 1.8 2.1 3.0 DISTANCE UPSTREAM FROM THE COLORADO RIVER,!N MILES Channel bed EXPLANATION Radiocarbon age, in years before present 1984 debris-avalanche deposits 1984 debris-flow deposit Pre-1984 debris-flow deposit Soil or incipient soil Stratigraphy hidden or not present Boulder 3 o t w o 06002 FIGURE 9.-Stratigraphy of debris-flow deposits in the Monument Creek drainage. has an average length of 8 ft and weighs an estimated 37 tons. Near the Colorado River, the deposits in the center of the channel abruptly change to well-sorted and imbricated boulder bars (fig. 8C) superficially resembling sieve deposits (Hooke, 1967). The debris flow at this point was confined and deposition occurred to an average depth of 5 ft. At locally unconfined sites, the critical thickness of the debris flow was 3 ft. The particle-size distribution (fig. 10D) shows a well-sorted cobble deposit with a median diameter of 32 mm, although poorly sorted matrix was found on the channel margin. We speculate that either recessional or post-event streamflow, dewatering of the deposit after deposition, or positive pore pressures from springs in the channel bed caused the nearly complete removal of the debris-flow matrix from the boulders and its subsequent transport into the Colorado River. DISCHARGE CALCULATIONS Superelevations resulting from the debris flow of 1984 were measured at three sites on Monument Creek in reaches 0.3, 0.5, and 1.5 mi upstream from the Colorado River. At Tapeats Alcove (site A, fig. 7), an elevation dif- ference of 4.7 ft was measured from mudlines on the wall of a prominent overhang. Channel geometry at the site (table 3) was used to calculate a velocity of 12 ft/s for the debris flow. The bed of the channel consists of large blocks of Tapeats Sandstone, which had fallen from the roof of the alcove either before or during the debris flow. The PARTICLE DIAMETER,IN 0 UNITS i- wad & J ---pe-4. Z “J . < g u 80, 7 a. gop 7 - 60} - I & | - Lu E: ¢}() " -| u E: < y. < 20} 7 _] D a D O i a 1 T i a i 1 O 256 16 I 0.063 0.004 PARTICLE DIAMETER,IN MILLIMETERS EXPLANATION A Avalanche deposit B Debris-flow deposit above site A C Debris-flow deposit at site B D Fan deposit at Colorado River FicurE 10.-Particle-size distributions of the debris flow of 1984 in the Monument Creek drainage. See figure 7 for locations of sites. MONUMENT CREEK DRAINAGE 13 cross sections measured at the superelevation mark and a wide, eroded reach upstream had twice the area of a cross section that was measured 50 ft downstream (table 3). We used the cross-sectional area measured 50 ft downstream (320 ft?) to calculate a peak discharge of 3,800 ft5/s for the debris flow. Reconstitution of a debris- flow matrix sample taken upstream indicates a water con- tent of 32 to 34 percent by volume. At site B (fig. 7), resistant Vishnu Schist forms the bed of the channel. A maximum superelevation of 3.7 ft was measured on this bend (fig. 11), which is 0.5 mi upstream of the Colorado River. A runup elevation of 2.1 ft was measured above the superelevation line. Velocities of 11.0 and 11.5 ft/s were calculated from the superelevation and runup evidence, respectively (table 4). As observed previously, cross sections in the bend had significantly larger areas than upstream and downstream cross see- tions; hence, the average of the upstream and downstream cross sectional areas (320 ft2; table 4) was used. The resulting discharge is between 3,600 and 4,000 ft/s, depending upon whether velocity was calculated from runup or superelevation evidence. The water content of the peak flow, reconstituted from a sample collected near the site, was 27 to 29 percent by volume. At site C, 0.3 mi from the Colorado River (fig. 7), super- elevation marks were preserved on a bend having con- siderable debris-flow deposition. No controls on channel depth are present in this reach and either aggradation or degradation may have occurred. Survey data revealed an ambiguous superelevation because of a slight channel ex- pansion (97 to 106 ft) over a 20-foot distance. Use of the respective elevation differences (8.4 or 4.6 ft) with the associated width resulted in a velocity between 11.9 and 13.2 ft/s. Possible deposition after the peak flow in upstream sections precluded any meaningful calculation of cross-sectional area. A cross section measured 45 ft downstream from the lower superelevation site yielded an area of 320 ft2, although the actual area might be con- siderably larger due to possible deposition after the peak flow. The resulting discharge ranged from 3,800 to 4,200 ft3/s with a Froude number between 1.2 and 1.4 (table 5). The water content of the flow was probably similar to that estimated for site B (28 percent). SEDIMENT VOLUME The new debris fan at the Colorado River (fig. 8) was surveyed to estimate the volume of material deposited during the debris flow of 1984. The debris flow entered and partially dammed the Colorado River (Mike Yard, boatman, Humphrey Summit Adventures, Flagstaff, Arizona, oral commun., 1986), which had a mean dis- charge of about 24,000 on July 25. Observers noted that the newly formed fan contained significant amounts of matrix immediately after the debris flow, but that the mud was quickly eroded from the fan. Higher discharges on the Colorado River in the fall of 1984 and spring of 1985 partially eroded the newly formed fan (Mike Yard, oral commun., 1986). Without knowing the exact geometric configuration of the fan after the event, a volume of sediment was esti- mated on the basis of four hypothesized scenarios of deposition (table 6) and extension of the debris fan remain- ing in 1986 into the Colorado River. First, we assumed the deposit that remained in April 1986 was the entire extent of the deposition; this scenario results in an un- realistically low estimate of sediment volume. Second, we assumed that the debris flow completely dammed the river at Granite Rapid; this seenario results in an unrealistically Maximum superelevation 40 FEET 10 METERS 120 100 EXPLANATION - zz» Channel bed - Cross-section location Inside-bend debris-flow marks --- QOutside-bend debris-flow marks 90 1 i 1 1 0 40 80 120 160 200 240 DISTANCE ON THALWEG, IN FEET ELEVATION , IN FEET ABOVE ARBITRARY DATUM FIGURE 11.-Plan map and longitudinal profile for indirect-discharge site B in Monument Creek, 0.5 mile upstream from the Colorado River. 14 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA high estimate of sediment volume. Two additional scenarios of partial damming of the river that more realistically paralleled the eyewitness report also were assumed. River depth at Granite Rapid was 11 ft at a discharge of 25,000 ft8/s in April 1984 (R.P. Wilson, U.S. Geological Survey, written commun., 1986). A triangular cross section was assumed for the 200-foot-wide channel. The depth of the fan deposit was estimated at 5 ft on the basis of natural exposures and the 3-foot depth of chan- nel filling was suggested from critical thicknesses of the deposit on the fan margin. The calculated volumes (table 6) indicate a range of possible volumes of sediment deposited during the debris flow. The most realistic estimate of sediment volume (scenario 3; table 6), with the debris flow partially dam- ming the river, is about 300,000 ft8. Using a measured sand content of 35 percent and assuming that all of the debris-flow matrix entered the Colorado River, thus ex- plaining the fines-depleted boulder bar, the estimated volume of sand-sized particles is 84,000 ft8 for this scenario. The estimated volume of sand ranged from 56,000 to 150,000 ft3 among the scenarios (table 6). This calculation indicates that a substantial volume of sand entered the Colorado River during the 1984 debris flow, although the exact volume is uncertain. Further assumptions were made concerning the debris fan to estimate the minimum elapsed time of the dis- charge. Sedimentologic evidence suggests a saw-toothed hydrograph of unknown duration (fig. 12). At least three recessional debris-flow surges followed the initial pulse although their stages were much lower (1-3 ft compared with greater than 10 ft). Similar multipeaked hydrographs of debris flows have been reported elsewhere (Hungr and others, 1984; Pierson, 1985). Flow between the surges may have been hyperconcentrated (see Pierson, 1985). We assumed that (1) the entire volume of material reaching the debris fan and the Colorado River was delivered in the first pulse and (2) the hydrograph shape could be modeled as a square wave with the recessional debris flows not reaching the debris fan (fig. 12). The resulting minimum duration times (table 6), which range from 1 to nearly 3 minutes, demonstrate the probable transitory nature of this event. ~ CRYSTAL CREEK DRAINAGE The Crystal Creek drainage, 48.3 mi? in area, is the largest of the three drainages studied (figs. 1, 13). The geology of this drainage consists of the Paleozoic section of Kaibab Limestone through the Muay Limestone that forms prominent cliffs in the headwaters, the nearly flat Tonto Platform developed on top of the Tapeats Sand- stone, and the Vishnu Schist forming deep canyons along the lower 5 mi of the drainage (Huntoon and others, 1986). The topographic relief in the drainage is 6,500 ft and the average channel slope is 0.07. 74 EXPLANATION g --- Hypothetical hydrograph 2 > p= - - Model of hydrograph peak o |- € 2 e o Tp Time of peak discharge Ns > 5 o | o 5 0 @ L 1 o *~ u 3 (R- » -* 3 s E a O > 3 8 3 kel o |I h 2 5 2 fo has u @ --- £000 $ > £ S o a (el 5 o a >n &- o z a sa-l -L- w 5 2 3 ------» - 8 o *~ [G] ® o re o a < h- £ O & pase ne reap o TIME , DIMENSIONLESS FIGURE 12.-Hypothetical hydrograph of the debris flow of 1984 in Monument Creek as suggested by stratigraphic evidence. CRYSTAL CREEK DRAINAGE 15 A debris flow occurred during the storm in December 1966 that also initiated a debris flow in the Lava-Chuar Creek drainage (Cooley and others, 1977). Because of the sustained nature of the storm, the flood consisted of streamflow of unknown discharge followed by a large debris flow and subsequent streamflow of moderate 12°13" I discharge (Cooley and others, 1977). The debris flow reportedly had either a single pulse or multiple pulses in the lower parts of the drainage. The debris flow started at 11 slope failures in the headwaters of Milk Creek (fig. 13) and travelled 13 mi through Milk Creek and down Dragon and Crystal Creeks to the Colorado River. 12°07" I EXPLANATION e=» Dobris floOW path X Slope failure A Destroyed mescal pit B Cooley indirect-discharge site C Indirect-velocity site D Tapeats narrows F,G - Indirect-discharge site H Debris fan and rock garden 36°15 |- Drainage AC 2C 7/ ° i021 /',/NORTH ./’RiM \ &* R & '_/ z". /* divide Drainage r boundary —\ Ne 36°%10° NATIONAL GEODETIC VERTICAL DATUM OF 1929 2 MILES 0 | 2 KILOMETERS CONTOUR INTERVAL 2000 FEET FIGURE 13.-The Crystal Creek drainage at mile 98.2 on the Colorado River. See figure 1 for location. 16 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA Streamflow that followed the debris flow partially obliterated the lower parts of mudlines and caused signifi- cant channel erosion (Cooley and others, 1977). The debris fan resulting from the debris flow of 1966 significantly constricted the Colorado River at Crystal Rapid. Cooley and others (1977) calculated discharges for the different phases of the flood from evidence at several sites in the Crystal Creek drainage. A peak flow of 100 was estimated for Crystal Creek above its confluence with Dragon Creek (fig. 13), indicating that this part of the drainage added little streamflow to the flood. In contrast, Cooley and others (1977) estimated a discharge of 29,000 ft3/s for the peak of the debris flow on Dragon Creek (site B, fig. 13) using the slope-area method and a Manning's n value of 0.070. Cooley and others (1977) calculated a velocity of 23 ft/s with a Froude number of 1.1 to 1.2 for the flow. A discharge of 1,000 ft8/s was estimated for streamflow on Dragon Creek upstream from the conflu- ence with Milk Creek. This discharge could have contrib- uted to the post-debris-flow streamflow in the drainage. The debris flow of 1966 caused considerable channel change and damaged archaeological and historical sites (Cooley and others, 1977). The archaeological site (site A, fig. 13), a mescal (agave-roasting) pit probably used be- tween A.D. 1050 and 1150, was inundated and could not be exactly located during post-flood surveys. Cooley and others (1977) concluded on the basis of this evidence that the debris flow was the largest event in 800 years with a recurrence interval of several centuries. In contrast, the recurrence interval for the flood of December 1966 on Bright Angel Creek (4,000 ft3/s) was estimated at 25 years. The 1966 debris flow obliterated a mine shaft 3 to 4 ft above the bed of Dragon Creek just upstream from its confluence with Crystal Creek (Harvey Butchart, retired professor, Northern Arizona University, oral commun., 1986). The destruction of this shaft, which was probably dug between 1893 and 1916, indicates that large floods or debris flows had not passed the confluence of Crystal and Dragon Creeks between 1916 and 1966. STRATIGRAPHY Most of the depositional record of prehistoric debris flows has been eroded from the Crystal Creek drainage because of the apparent high frequency of events. Stratigraphic sections (fig. 14) indicate at least three prehistoric debris flows have passed through the 2.5-mile reach of Crystal Creek upstream from the Colorado River. A radiocarbon age of 180 +70 yr B.P. (AA-1784) from wood entrained in the lowermost of the debris-flow deposits suggests that a minimum of three debris flows have occurred in 200 years. On the basis of sedimentologic characteristics, longitudinal correlations of the deposits indicate that at least two of these flows reached a point 2.1 mi above the Colorado River. Although we found no stratigraphic evidence of old flows between mile 2.1 and the mouth, it is reasonable to assume that the three prehistoric debris flows reached the Colorado River. In Tapeats Narrows on Dragon Creek (site D, fig. 13), an exceptional exposure of stratigraphy revealed a com- plex depositional record of at least seven debris flows beneath the 1966 deposit. Interbedded sand and debris- flow deposits and complex cut-and-fill structures in the stratigraphy indicate a fluctuating bed in Dragon Creek that existed in response to debris flows. A radiocarbon age of 355 +70 yr B.P. (AA-1786) near the base suggests that six of these flows occurred in the last 300 to 400 years. A radiocarbon age of 130 +50 yr B.P. (AA-1785) on a layer of accumulated organic debris beneath the last flow before 1966 and a "modern" (near A.D. 1950; A-4541) age on the bark of a buried tree (fig. 14) suggests a high frequency of events at this site. We interpret the radiocarbon age on the tree as more reliable than the age on the litter layer. Debris flows occur more frequently in the Crystal Creek drainage than the frequency stated by Cooley and others (1977). The 1966 debris flow is the only historic event preserved in the stratigraphy; however, evidence for lower-stage, historic debris flows may have been obliter- ated in 1966. On the basis of stratigraphy preserved in the lower part of the drainage, four debris flows (including the one in 1966) have reached the Colorado River in 200 years. Therefore, a debris flow that is large enough to reach the Colorado River occurs approximately every 50 years. Smaller debris flows occur at about the same fre- quency near the headwaters and significantly aggrade the channel and possibly store sediment in advance of larger debris flows that are capable of reaching the Colorado River. Relocation of the camera position for photographs taken in 1967 (Cooley and others, 1977; figs. 7, 33, 34B, and 37) provided evidence for the longitudinal extent of a debris flow that occurred after 1966. At site A (fig. 13), debris-flow deposits fill the 1967 channel bottom by 2 to 3 ft, and a prominent headcut on a side channel (Cooley and others, 1977, fig. 33) has migrated upstream 5 to 10 ft. Flow past the site of Cooley and others' indirect- discharge measurement (site B, fig. 13) shifted large boulders but caused little aggradation. The major change that is apparent in the matched photographs is the collapse of the vertical banks that were present in 1967 (fig. 15). Resurvey of this site revealed that the channel had widened by 5 to 15 ft, small talus deposits had en- croached on the channel from the banks, and no aggrada- tion had occurred on the bedrock channel. Changes caused by the post-1966 debris flow are less apparent down- stream, although minor changes were observed in a com- parison of aerial photographs of the fan deposit at the mouth of Crystal Creek taken in 1973 and 1984. CRYSTAL CREEK DRAINAGE LONGITUDINAL VARIATION IN THE 1966 DEBRIS-FLOW DEPOSITS We found stratigraphic evidence to support both the se- quence of fluvial events and a multiple-pulse debris flow reported for the flood of 1966 (Cooley and others, 1977). We based much of our interpretation and identification of deposits on photographs of Crystal and Dragon Creeks contained in Cooley and others (1977); these sites were relocated in 1986. Our descriptions provide additional in- sights into the nature of debris flows in this drainage and are not intended to supersede those of Cooley and others (1977). 20r 1966 an f 6 HEIGHT OF DEPOSITS, IN FEET 17 Stratigraphic sections between 4 and 5 mi upstream from the Colorado River had "sandy sole layers" (Scott, 1985), consisting of relatively well-sorted, friable sand and gravel deposits (fig. 16), which underlie the poorly sorted debris-flow deposit. Sole layers have been interpreted as a debris flow interacting with streamflow at the front of the initial pulse (K.M. Scott, U.S. Geological Survey, oral commun., 1986). Streamflow probably was hyperconcen- trated with sediment and may have been pushed down the channel by the more rapidly moving debris flow. The presence of sole layers supports the hypothesis of a flood preceding the debris flow (Cooley and others, 1977). 1966 O w ..H # 0 ay It 11 rola ) O n .H O & 1-1 5 se > + 0 w - w o 10 0 o Dragon Creek (Tapeats Narrows) A 0.7 2.1 2.3 2.5 Channe! bed 3.5 4.1 4.4 DISTANCE UPSTREAM FROM THE COLORADO RIVER,IN MILES EXPLANATION Radiocarbon age, in years before present Hyperconcentrated or streamflow deposit Stratigraphy hidden or not present igo +70 1966 debris-flow deposit Pre-1966 debris-flow deposit CIW ZT] - Soil or incipient soil o © Boulder FIGURE 14.-Stratigraphy of debris-flow deposits in the Crystal Creek drainage. 18 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA FIGURE 15.-Dragon Creek, 6.2 miles upstream from the Colorado River. The piece of driftwood at the left center of view B (April 1986) is not the same piece as in view A (February 1967). Note in view B that the large rocks at the upper left and right have been moved downstream and the bank has collapsed in the foreground. Flow in the channel moves right to left. CRYSTAL CREEK DRAINAGE 19 The debris flow of 1966 left considerable stage and sedimentologic evidence of its passage in the Crystal Creek drainage. In Tapeats Narrows (site D, fig. 13), mudlines were observed 40 ft above the current channel. The red color of debris-flow matrix contrasted greatly with the brown soils on terraces and hillslopes. The damaged mescal pit (site A, fig. 13) was buried under 0.1 to 0.6 ft of red matrix deposit. The site, on the outside of a slight river bend, was inundated by the superelevated debris flow, but erosion was slight. Downstream, terraces of approximately the same height were not inundated. Debris-flow deposits and mudlines have been preserved along the 4.5 mi of Crystal Creek below its confluence with Dragon Creek (fig. 13). The flow from Dragon Creek blocked Crystal Creek at the confluence with a 13-ft-high boulder deposit. Debris-flow deposits from Dragon Creek were found 300 ft upstream along Crystal Creek. Down- stream, the debris flow entered a steep bedrock canyon in the Vishnu Schist and left mudlines as much as 20 ft above the current channel bed. Evidence for recessional debris flows after the main peak was preserved in the 2.5-mile-long reach upstream of the Colorado River. The heights of the recessional debris-flow deposits, which create a sawtooth appearance on the floodplain, are ap- proximately 5 and 6 ft below the high-water marks for the main debris-flow pulse at site G (fig. 13). The effects of the debris flow of 1966 on Crystal Rapid are well known (Collins and Nash, 1978; Kieffer, 1985; Stevens, 1983). The debris flow almost certainly dammed the Colorado River temporarily until subsequent flows eroded through the left (south) side (Kieffer, 1985). In 1965, the width of the Colorado River at Crystal Rapid was approximately 280 ft at a discharge of 48,000 (Bill Emmett, U.S. Geological Survey, written commun., 1986). In March 1967, the width was only 100 ft at a discharge of about 10,000 ft8/s (Cooley and others, 1977). Maps prepared by S.W. Kieffer (U.S. Geological Survey, written commun., 1986) from aerial photographs taken in 1984 indicate a width of 130 ft at a discharge of 5,600 ft3/s. A comparison of photographs of Crystal Rapid taken in 1966 and 1986 (fig. 17) documents the persisting changes. The rock garden (site H, fig. 13), or debris bar, located below the rapid and formed from outwash from the fan at the mouth of Crystal Creek, was substantially increased as a result of the debris flow. Photographs in Collins and Nash (1978) taken at low discharge in the Colorado River show a pre-1966 debris bar at the site of the present debris bar, but aerial photographs taken in 1965 at a discharge of 45,000 ft%/s reveal no obvious debris bar. DISCHARGE CALCULATIONS Velocities and discharges were calculated for the peak of the debris flow of 1966 from mudlines and deposits in the Crystal Creek drainage. At site C (fig. 13), a tight, nearly 180° bend in Dragon Creek, an elevation difference of 11.9 ft was measured between the high-water marks in cacti and shrubs on the inside and outside of the bend. Based on a radius of curvature of 36 ft and width of 103 ft, the debris flow had a mean velocity of 11.5 ft/s. The discrepancy between the radius of curvature and the width may invalidate the assumption that all streamlines follow the radius of curvature (see section '"Hydraulies of Debris Flows"). The channel had significantly aggraded after 1966, and cross sections necessary for a discharge calculation could not be surveyed. Below Tapeats Narrows, a runup deposit preserved under an overhanging ledge of Tapeats Sandstone pro- vided an opportunity to estimate the discharge for the debris flow of 1966 (site E, fig. 13). We calculated a mean velocity of 15.9 ft/s from the runup evidence (table 7). One cross section with an area of 710 ft? was measured at the runup site and resulted in an estimated discharge of 11,300 ft3/s. The longitudinal variation in cross-sectional area was not investigated at this site, but it may have been substantial. Photographs from Cooley and others (1977) were used to reconstruct high-water marks at site F (Cooley site number Ariz. B:16:42). The prominent superelevation PARTICLE DIAMETER,IN # UNITS -10 -6 -2 _o _ 2 6 10 _ 100 T t- T T T T ® ‘ Z 8 [~ 7 i &C so} - D- ..- E -I ° 60)- ~ I & |- - w . 3 40}|- © - id . > Lo / I - i- /' ' GI 20} . Sole layer - 3 / ill— 3 / ,/ / O 0 a -I 1 1 1 1 1 1 1 1024 64 4 06 0.25 6.016 PARTICLE DIAMETER ,IN MILLIMETERS EXPLANATION «-+- COARSE-GRAINED FACIES-Site G, 0.9 mile upstream from Colorado River --- FINER GRAINED DEPOSIT-Site G, 0.9 mile upstream from Colorado River -- DEBRIS-FLOW DEPOSITS-Confluence of Crystal and Dragon Creeks, 4.5 miles upstream from Colorado River FigurE 16. -Particle-size distributions of the debris flow of 1966 in the Crystal Creek drainage. See figure 13 for locations. 20 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA marks (Cooley and others, 1977, fig. 16A) were relocated and surveyed. Elevation differences between terraces, mudlines, and the channel bed reported in Cooley and others (1977, fig. 36) indicated no net aggradation or deposition in the intervening 18 years. Relocation of the sites (especially Cooley and others, 1977, fig. 340) re- vealed local channel widening upstream from the bend. Although the channel changed slightly between 1967 and 1986, no evidence for post-1966 debris flows was found at this site. We surveyed a longitudinal profile of mudlines and measured an elevation difference of 22.7 ft between lines on the inside and outside of the bend (table 8). The longitudinal profile (fig. 184) shows an increase in the slope of the channel bed at the start of the bend that may have affected the flow regime. The mescal pit at this site (Cooley and others, 1977) was narrowly missed by a lower- stage superelevation on an upstream bend (fig. 184). Mean velocity on the larger bend was calculated to be 17.7 ft/s. Surveyed cross sections indicate that the area at the highest superelevation marks is nearly three times larger than upstream and downstream areas (table 8). On the basis of an average area of upstream and downstream cross sections, we calculated a discharge of 14,000 for the 1966 debris flow, although we estimate a numerical uncertainty of between 11,900 and 15,400 ft8/s. The water content of the flow, reconstituted from a sample taken 0.3 mi downstream, was 24 to 26 percent by volume. At site G, 0.9 mi upstream from the Colorado River, superelevation and runup marks were preserved on the walls of Vishnu Schist and in cacti. Superelevation evidence (fig. 18B) was used to calculate a mean velocity of 10.3 ft/s (table 9). However, mean velocities calculated from runup evidence at two points (fig. 18B) were 15.0 and 15.4 ft/s. As noted at all other superelevation sites, the area of cross sections measured near superelevation % FIGURE 17.-Crystal Rapid at the mouth of Crystal Creek. The poor visual quality of view A (May 1966) results from deterioration of the original color slide. Note the small debris fan and smooth tongue of water entering the rapid at right center of the river. The discharge of the Colorado River is 16,000 cubic feet per second. In view B (April 1986), the tongue of the rapid has been forced to the left as a result of the debris fan deposited during the debris flow of 1966. The discharge of the Colorado River is 28,500 cubic feet per second. SIMILARITIES AND CONTRASTS AMONG THE DRAINAGES 21 marks were significantly larger than the areas of cross sections upstream and downstream from the marks (table 9). We estimated a discharge of between 9,200 and 13,500 ft3/s for the debris flow on the basis of the range in velocities and cross-sectional areas. The water content of the flow, reconstituted from a sample taken 0.1 mi down- stream, was 31 to 33 percent by volume. Particle-size distributions (fig. 16) show that extremely coarse, poorly sorted sediments were transported during the debris flow of 1966. The sediments contained 10- to 15-percent sand and 5- to 10-percent silt and clay (fig. 16); different samples had similar particle-size distributions except in a coarse facies found 0.9 mi above the Colorado River. Boulders 7 ft in diameter were common in levee deposits. One boulder measured at site G was a rectan- gular block that had dimensions of 14x7x6 ft and weighed an estimated 49 tons. Nine other boulders on this (0.1-mile-long levee had intermediate diameters in excess of 5 ft. Similar-sized boulders are found in the debris fan at the mouth of Crystal Creek (S.W. Kieffer, U.S. Geological Survey, written commun., 1986). SIMILARITIES AND CONTRASTS AMONG THE DRAINAGES The debris flows of 1966 in the Crystal Creek and Lava- Chuar Creek drainages and the debris flow of 1984 in the Monument Creek drainage have similar characteristics. The debris flows all were initiated by slope failures in the Hermit Shale and the Esplanade Sandstone during an in- tense storm event. All three debris flows transported a poorly sorted mixture of clay- to boulder-size particles in slurries. Water contents ranged from 23 to 33 percent during the initial peak. The flows were followed by reces- sional debris and (or) hyperconcentrated flows that deposited distinctive sawtooth-shaped levees on the flood plain. Peaks of the debris flows reached the Colorado River, and two of the three debris flows caused signifi- cant constrictions of the Colorado River at the tributary mouth. Our limited data suggest an important mechanism of channel adjustment following debris flows that reached the Colorado River. As illustrated by the stratigraphy in Tapeats Narrows of Dragon Creek (fig. 14), not all debris FIGURE 17.-Continued. 22 flows reach the Colorado River. Small debris flows fill the headwater channels with sediments after they stop flow- ing and raise the bed elevation by tens of feet. Subsequent flows of larger volume may be able to erode through this stored sediment and incorporate it into the moving fluid. Smaller debris flows may prime the channel for larger debris flows that have sufficient volume of sediments to reach the Colorado River. We determined a significant problem with the measure- ment of the effective flow area of debris flows at all sites where discharges were estimated. The cross-sectional areas at the superelevation marks are 1.3 to 3.6 times larger than upstream or downstream areas (table 10). Discharges calculated using the areas at superelevation DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA marks, therefore, are 1.3 to 3.6 times larger than those calculated using the upstream and downstream areas (table 10). If the cross sections at the superelevation marks are used, continuity of flow (equation 4) implies substantially higher velocities on the approaches and exits to the bends. Using site F in the Lava-Chuar Creek drainage as an example, the exit velocity would be 43 ft/s if the cross-sectional area at the superelevation marks were fully effective during the peak of the debris flow. The velocity would have increased 31 ft/s in 250 ft with no significant slope change under these conditions. Discharges were estimated from upstream and (or) downstream cross-sectional areas and assumed that the velocity was not significantly changed through the bend 110 t t t t u T u T Small bend near roasting pit i 60 r i 40 80 120 160 200 240 280 DISTANCE ON THALWEG,IN FEET 320 360 400 440 560 ELEVATION, IN FEET ABOVE ARBITRARY DATUM 0 1 T a i Bo 120 160 200 240 280 320 360 400 DISTANCE ON THALWEG,IN FEET EXPLANATION »»»» Channel-bed elevation | - Cross-section location - -- Inside-bend debris-flow surface Outside-bend debris-flow surface FIGURE 18.-Longitudinal profiles for indirect-discharge sites in the Crystal Creek drainage. A, Site F, 4.8 miles upstream from the Colorado River. B, Site G, 0.9 mile upstream from the Colorado River. FLUVIAL EVENTS IN OTHER DRAINAGES 283 by energy losses. Several hydraulic properties of debris flows can be used to support the latter assumption. Because of their cohesive nature, debris flows may have large ineffective flow areas consisting of static sediment on the margins of channel bends. Superelevation formulae are used to calculate not only a mean velocity across a cross section but also a mean velocity around part of the bend. For example, Apmann (1973) uses the curvature angle of the bend in his formula, implying that supereleva- tion is a function of both longitudinal and mean cross- sectional velocity. Finally, the low turbulence and high momentum of debris flows probably reduces longitudinal variations in velocity. Calculation of velocities of debris flows using superelevation evidence appears to involve a considerable error that could not be estimated in this study. The three drainages that we studied had different fre- quencies for debris flows reaching the Colorado River. We could not estimate a true magnitude-frequency relation because we estimated discharges only for a single flow in each drainage. Relative stages of successive debris flows were determined; however, channel changes be- tween events may have changed the stage-discharge rela- tion for the channel. The Lava-Chuar Creek drainage had the most frequent debris flows that reached the Colorado River with an average of one event every 20 to 30 years. Monument Creek had at least two debris flows this cen- tury, and they both occurred within 25 years. Crystal Creek had only one debris flow reaching the Colorado River this century and averages a minimum of one debris flow every 50 years that reaches the Colorado River. The size of transported boulders varied considerably among the drainages. The largest boulder transported by the debris flow of 1966 in the Lava-Chuar Creek drainage weighed an estimated 9 tons. Boulders that were trans- ported in the Monument and Crystal Creek drainages weighed an estimated 37 and 49 tons, respectively. In all drainages, larger boulders may have been transported into the Colorado River. The sand content of the flows ranged from 10 to 40 percent and represents a potential- ly significant source for beach sands along the Colorado River. FLUVIAL EVENTS IN OTHER DRAINAGES As previously stated, debris flows are common phenomena in Grand Canyon National Park. Individual drainages such as Lava-Chuar Creek may average 20 to 30 years between debris flows that reach the Colorado River; in the park as a whole, however, such flows occur much more frequently. We gathered historical informa- tion and analyzed aerial photography from 1965, 1973, and 1984 to compile a list of historical fluvial events from ungaged tributaries that have affected their debris fans at the Colorado River (table 11). We also list known historic debris flows and floods in table 11. The list is not all inclusive, because more than one flow could have in- duced the changes and not all floods were debris flows. However, the list provides a perspective on the frequency of fluvial events, many of which were debris flows, be- tween 1965 and 1986. In the historical record, the summer of 1983 probably was the most significant year for fluvial events from ungaged tributaries. Rainfall was above average during July and August. On July 25, Grand Canyon, Bright Angel Ranger Station, and Phantom Ranch had 3.14, 2.02, and 1.85 in of rainfall, respectively. No intensity data are available for this storm; however, the daily totals suggest pervasive storms in the Grand Canyon on July 25. Almost all the drainages between Colorado River mile 42 and mile 77 had flash floods during the summer of 1983 (table 11), possibly during the storm on July 25. Sediment-sampling data from the gaging station on the Colorado River at Phantom Ranch shows small peaks in sediment during July and August 1983, which may be attributable to these floods. A winter storm in December 1966 caused widespread flooding within Grand Canyon National Park (Cooley and others, 1977). A storm originating in the north Pacific Ocean traveled slowly over northern Arizona and south- ern Utah between December 3 and 6 (Butler and Mun- dorff, 1970). Floods on the Virgin River in southern Utah exceeded the 100-year event (Butler and Mundorff, 1970), suggesting that this type of storm is rare. Precipitation totaling 11 to 14 in. fell on the North Rim (Cooley and others, 1977), triggering floods in Bright Angel Creek and several other drainages with headwaters on the Kaibab Plateau. The debris flows in the Lava-Chuar and Crystal Creek drainages (see "Debris Flows in Three Tributaries of the Colorado River") and ten other debris flows not reaching the Colorado River were initiated during this storm (Cooley and others, 1977). In July 1984, a debris flow with a stage of greater than 7 ft and width of 200 ft struck two 20-ton trucks stalled in the channel of Diamond Creek about 0.5 mi upstream from the Colorado River (Mike Walker, boatman, O.A.R.s, Modesto, California, oral commun., 1986). The trucks were carried into the river and later were found more than 1,000 ft downstream on the opposite bank. Boulders 4 to 5 ft in diameter were transported by the debris flow, which remained at uncrossable levels for 6.5 hrs. The debris flow reportedly caused 30-foot-high spray upon im- pact with the Colorado River and greatly enlarged the debris fan. This brief history indicates that several storm types may initiate fluvial events, which include debris flows, in the Grand Canyon. Summer thunderstorms appear to be the most common type of storm that initiates debris flows. These storms generally are localized in one or two adja- 24 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA cent drainages and can be considered as random in time. Intense precipitation resulting from winter frontal storms also may initiate debris flows; however, this type of storm generally is rare. FACTORS RESPONSIBLE FOR DEBRIS FLOWS The bedrock geology of Grand Canyon National Park controls the location of the initiation sites for debris flows in tributaries of the Colorado River. The Grand Canyon is noted for spectacular cliffs of sedimentary rocks, and the combination of stratified rocks with different strength properties and high relief leads to a high potential for slope failures (Rogers and Pyles, 1979). In addition, fault planes control the location of drainages in Grand Canyon (Dolan and others, 1978; Potochnik and Reynolds, 1986), and the resultant shear zones provide abundant loose and poorly sorted material for debris-flow initiation. Abundant talus accumulates locally beneath cliff faces, providing a source for debris mobilization during intense storm events. The Grand Canyon is, in fact, an ideal location for debris flows. The most common cause for debris flows is slope failures in the Hermit Shale and Supai Group throughout the Grand Canyon. In the only systematic mapping of slope failures, Cooley and others (1977) mapped 93 slope failures that occurred during the storm of 1966. Seventy percent were from the Hermit Shale and Supai Group; 19 percent from the Kaibab Limestone and underlying Toroweap Formation, or Coconino Sandstone; and 11 percent from the Muay Limestone. Most of these failures resulted in local debris flows, and failures in the Hermit Shale and the Supai Group initiated debris flows in the Lava-Chuar and Crystal Creek drainages that reached the Colorado River. The composition and chemistry of the Hermit Shale and Esplanade Sandstone have the potential to generate debris flows. The Esplanade Sandstone at the top of the Supai Group consists of alternating layers of sandstone, siltstone, and mudstone and forms a morphologically distinct series of basal slope, cliff, and upper slope (McKee, 1982). This formation is of continental origin, which contrasts with the marine origin of the other three for- mations of the Supai Group. Swelling clays, notably smee- tites and montmorillonites, are abundant in these rocks (McKee, 1982) and cause rapid weathering of the cliffs into potentially mobile talus. Both the Hermit Shale and Esplanade Sandstone contain dispersive clays, which disintegrate into colloidal suspension when water is added (J.D. Rogers, Rogers/Pacific Consultants, Lafayette, California, oral commun., 1986). When these rocks are located on top of cliffs of Redwall Limestone, catastrophic slope failures are possible as the rocks weather. The combination of alternating rock types, dispersive clays, and the high relief in the drainage basins make canyons with exposures of Hermit Shale and Esplanade Sandstone particularly susceptible to debris flows. The proximity of these rocks to the Colorado River may ex- plain some of the longitudinal spacing of rapids. The Roar- ing Twenties (fig. 1) are a series of closely spaced, moderate-size rapids that occur where the Hermit Shale and Supai Group are first elevated above the river. In con- trast, few moderate to large rapids occur between Kanab Creek and Prospect Creek (fig. 1), possibly because the Hermit Shale and most of the Esplanade Sandstone have been stripped from the nearby cliffs. Several drainages exemplify other sources of sediments for debris-flow mobilization in Grand Canyon National Park. Red Canyon (fig. 1) has formed at the intersection of several major faults, and two large landslide deposits have been mapped in its headwaters (Huntoon and others, 1986). Hance Rapid is formed where a debris fan from Red Canyon forces the Colorado River against a bedrock wall. Large boulders in the channel cause severe naviga- tional difficulties at low water (Stevens, 1983). Debris flows from Red Canyon have occurred relatively frequent- ly in geologic time as indicated by the large debris fan, multiple levees, and exposed debris-flow stratigraphy. The large landslides and shear zones in the headwaters are the probable source of sediments for the debris flows. Lava Falls Rapid, generally regarded as the most dif- ficult to navigate on the Colorado River (Collins and Nash, 1978), is formed by debris transported from Prospect Creek (fig. 1) and not by outcrops of resistant rocks (Leopold, 1969). Four large basalt boulders form the in- famous Ledge Hole in the center of the rapid. The fan at the mouth of Prospect Creek consists of four inset ter- races, each of which is composed of multiple debris-flow deposits. The source of sediments for debris flows is the loose basalt talus in the shear zone of the Toroweap fault about 1 mi from the Colorado River (Huntoon and others, 1981). Discharges in Prospect Creek cascade over a 1,200-foot cliff and initiate slope failures in the loose talus. The occurrence of debris flows is not controlled by an obvious basin morphometric factor in Grand Canyon National Park. Similar adjacent basins appear to have completely different histories of debris flows. For exam- ple, Monument Creek has had two debris flows that reached the Colorado River in 25 years and Hermit Creek, slightly larger in size and abutting Monument Creek on the west, has had no obvious debris flows that reached the river during the same period. Although the storm of December 1966 initiated a debris flow in the Crystal Creek drainage, the adjacent and larger Shinumo Creek drainage had only small debris flows in its headwaters, and only streamflow reached the Colorado River (Cooley and others, 1977). Clearly, debris flows that reach the Colorado River are a random occurrence controlled by the combination of accumulation rates of sediment available for transport and intense storm events. HYDROLOGIC EFFECT OF DEBRIS FLOWS ON THE COLORADO RIVER 25 An attempt was made to explain the navigational difficulty and water-surface fall through 67 rapids of the Colorado River on the basis of contributing drainage areas of tributaries (table 12). Although navigational difficulty and water-surface fall through a rapid are not good pre- dictors of the frequency or size of debris flows from the tributaries, they are the only known characteristics avail- able for the entire Colorado River corridor. Drainage- basin area is the hydrologic variable most commonly used to assess regional flood and sediment-transport potential. All rapids with a maximum rating greater than 4 (Stevens, 1983) are included with the exception of Lower Lava Rapid, which is controlled by outwash debris from Lava Falls Rapid and Prospect Creek, and Nixon Rock Rapid, which is controlled by rockfalls. Selected rapids with a maximum rating of 4 or less were also included (table 12). With the exception of the Paria and Little Colorado Rivers, all drainages included had obvious debris-flow deposits at the Colorado River. Drainage areas of contributing tributaries do not ex- plain either water-surface fall or navigational difficulty of rapids on the Colorado River (fig. 19). Local channel factors also cannot explain these variables because rapids with similar navigational difficulties have different water- surface falls and constriction ratios (S.W. Kieffer, U.S. Geological Survey, written commun., 1986). Local chan- nel conditions such as bedrock spurs and confining-wall geometry may exacerbate a rapid. We attribute the non- correlation of drainage area and rapid difficulty to the overwhelming control of rapid difficulty by local factors in each contributing drainage, particularly the size of debris-flow-transported boulders, the history of debris flows, and local channel conditions. HYDROLOGIC EFFECTS OF DEBRIS FLOWS ON THE COLORADO RIVER The magnitude and frequency of debris flows control the hydraulics of the Colorado River in Grand Canyon National Park. Debris flows from small tributaries ag- grade fans which typically force the river against the opposite wall of the canyon (fig. 20). In some cases, debris fans from tributaries on opposite sites of the river, such as the Lava-Chuar Creek drainage and Palisades Creek, constrict the Colorado River without a directional change. Debris flows deposit very large boulders in the river that cannot be moved by ordinary discharges. Therefore, rapids tend to be maintained as hydraulic controls on the river until the boulders can be moved by rare, large discharges (Graf, 1979). The ability of small drainages such as Monument Creek to control the hydraulics of one of the largest rivers in the United States is of great hydrologic significance. The combination of a debris fan and the increased velocity of flow in the rapid creates flow-separation zones conducive to the formation of beaches (Schmidt and Graf, 1988). Constriction ratios at debris fans range from 0.3 to 0.7 (Kieffer, 1985), and separation zones (and conse- quently beaches) form upstream and downstream from rapids. The combination of sudden channel expansion and rapid deceleration of flow below rapids induces the recirculating-eddy systems common in Grand Canyon National Park (Schmidt and Graf, 1988). Debris-flow transport of boulders onto the fan surfaces is the key process in creating the system of flow separations on the Colorado River. Control of local channel hydraulies extends beyond the rapid and debris-fan system. Prominent debris bars, referred to as islands or rock gardens, are formed down- stream from the rapid by reworking of the debris fans after a debris flow. Commonly on the opposite side of the river from the tributary, these bars generally are com- posed of well-sorted, imbricated cobbles and boulders mixed with sand. At Crystal Creek, the rock garden was IOLA e e RATING 25+ O 20) wATER-SURFACE FALL,IN FEET a ina ia a ica =a 1 aclu 0.01 0.! I 10 100 1000 10,000 DRAINAGE AREA,IN SQUARE MILES FIGURE 19.-Relation of characteristics of rapids and the contributing drainage area of the tributaries. A, Using the "rapid rating" (scale of 1 to 10; Stevens, 1983) for a discharge of 10,000 cubic feet per second in the Colorado River. B, Using the water-surface fall surveyed in 1921 and adjusted to 10,000 cubic feet per second. This fall may have significantly changed as a result of historic debris flows, especially at Crystal Rapid. 26 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA greatly enlarged after the debris flow of 1966 and con- tains boulders that are unusually large for a debris bar. At Monument Creek, the island enlarged slightly after the 1984 debris flow. An island in the Colorado River at river mile 66 (Stevens, 1983) appears to be maintained by periodic debris flows from the Lava-Chuar Creek drainage and Palisades Creek. Debris bars, particularly in the form of islands, provide a control on the longitudinal extent of eddy systems. Large debris bars induce second- ary riffles or rapids, such as Lower Lava Rapid at river mile 179.8, that may be additional navigational hazards or form secondary flow-separation zones. Debris flows from tributaries have important influences on sediment transport in the Colorado River. Although the debris flows occur infrequently, they are the source of large volumes of sand that enter at discrete points along the river. Debris flows transport boulders into the Colo- rado River that create the hydraulic controls that are prominent in the longitudinal profile of the river (Howard and Dolan, 1981). Debris fans and bars control the for- mation and longitudinal extent of separation zones needed to trap sand. A thorough understanding of the magnitude and frequency of debris flows is of paramount importance (Modified from Hamblin and Rigby , 1968) EXPLANATION Tributary debris fan Rapid controlled by large immobile boulders Debris bar (synonymous with "island" or "rock garden") Riffle or rapid caused by debris bar B G No- FIGURE 20.-Geomorphic features of a typical rapid controlled by debris flows on the Colorado River. to understanding and long-term estimates of sediment transport in the Colorado River in Grand Canyon National Park. SUMMARY Sediment transported from small drainages is a poten- tially large source of sand for beaches on the Colorado River in Grand Canyon National Park. Previous flood reports (Cooley and others, 1977) and recent mapping of alluvial deposits in tributary canyons during this project indicate that debris flows are a major process of sediment transport in small drainages in Grand Canyon National Park. Debris flows are common in arid and semiarid regions, but their importance in supplying sediment to the Colorado River has not been previously recognized. We observed debris-flow deposits in all 36 tributaries of the Colorado River that were examined during this study. Twenty-one of the 36 tributaries have evidence for debris flows within the last 25 years. We selected three tributaries for more detailed study on the basis of previous reports of debris flows. The tributaries studied in detail are the Lava-Chuar Creek drainage at Colorado River mile 65.5, the Monument Creek drainage at river mile 93.5, and the Crystal Creek drainage at river mile 98.2. Evidence for at least five prehistoric debris flows and three historic debris flows is preserved in the Lava-Chuar Creek drainage. Historic debris flows occurred between 1973 and 1984, in December 1966, and between 1916 and 1966. Debris flows have reached the Colorado on the average every 20 to 30 years since 1916 and every 190 years over the last 1,500 years. Debris flows may reach the Colorado River more frequently because not all prehistoric debris flows may have overtopped the terraces to leave depositional evidence. The debris flow of 1966 in the Lava-Chuar Creek drain- age had a velocity of 12 ft/s and a discharge of about 4,000 ft3/s near the Colorado River. The debris flow began at slope failures in the Hermit Shale and Supai Group and traveled 6.5 mi to the Colorado River. The water content of the flow was estimated at 22.5 percent and yielded sedi- ment and water discharges of 3,100 and 900 ft3/s, respec- tively. The debris flow had 30 to 35 percent sand and carried boulders 1 to 2 ft in diameter. The largest boulder measured that was transported during the 1966 debris flow weighed an estimated 9 tons. Two debris flows have occurred in the last 25 years in the Monument Creek drainage. A storm on July 27, 1984, initiated an avalanche and subsequent debris flow that reached the Colorado River. Scanty evidence suggests an earlier debris flow that occurred in the early 1960's. Older debris-flow deposits were radiometrically dated at about A.D. 1780, but lack of correlation with downstream deposits precluded any use of this date for determining frequencies of events. REFERENCES CITED 27 The debris flow of 1984 in Monument Creek began as an avalanche from the Esplanade Sandstone of the Supai Group 2,000 ft above the channel. A 20-foot high ava- lanche deposit still dammed the channel in 1986. The debris flow traveled 2.8 mi to the Colorado River at a velocity of 11 to 13 ft/s and a peak discharge of about 3,800 ft5/s. The water content of the flow ranged from 27 to 34 percent and the flow was composed of 30 to 40 percent sand. One boulder transported during the flow weighed an estimated 37 tons. The debris flow of 1984 created a new fan surface at the Colorado River that significantly constricted Granite Rapid. We estimated the volume of sediment transported onto the fan and into the river on the basis of hypothe- sized scenarios of post-debris-flow fan geometry. The most likely volume of sediment transported onto the fan and into the river is 300,000 ft3. The absence of particles less than 16 mm in diameter on the debris fan in 1986 sug- gests that all finer particles including sand were quickly transported into the Colorado River. By assuming an average sand content of 35 percent, the estimated volume of sand that entered the river is 84,000 ft3 with a range of 56,000 to 150,000 ft3 for the scenarios that were con- sidered. From the volume of sediment moved and the discharge estimated upstream, we estimated that the fan was created during the first pulse of the debris flow in 1 to 3 minutes. The Crystal Creek drainage has averaged a minimum of one debris flow that reached the Colorado River every 50 years. A large debris flow in 1966 has been the only debris flow to reach the Colorado River in this century. Small debris flows, on reaching the Colorado River, have significantly aggraded the channel in the past, possibly storing sediments available to larger debris flows capable of reaching the river. The debris flow of 1966 in the Crystal Creek drainage began at 11 slope failures in the Hermit Shale and Supai Group and traveled 13 mi to the Colorado River. The calculated flow velocity ranged from 10 to 18 ft/s, and the discharge ranged from 9,200 to 14,000 ft8/s. The water content of the flow ranged from 24 to 33 percent, and the sediments had a sand content of 10 to 15 percent. One boulder transported by the debris flow weighed an estimated 49 tons, and boulders with diameters in excess of 5 ft were commonly transported. Upon reaching the Colorado River, the debris flow created a new fan sur- face that significantly constricted the Colorado River. The debris flows studied had similarities that indicate the cause and nature of debris flows in Grand Canyon National Park. All three debris flows were initiated at slope failures in the Hermit Shale and Supai Group, especially the Esplanade Sandstone. All debris flows transported a poorly sorted mixture of clay- to boulder- sized particles with water contents ranging from 23 to 33 percent by volume. The largest boulders transported ranged from 9 tons in the Lava-Chuar Creek drainage to 37 and 47 tons in the Monument Creek and Crystal Creek drainages, respectively. Two of the three debris flows significantly constricted the Colorado River at the tribu- tary mouths. The frequency of debris flows that reach the Colorado River is tentative, but the available data sug- gest one flow reached the Colorado River every 20 to 50 years in these drainages. A compilation of the scanty historical information on flow events from Grand Canyon tributaries, however, indicates that debris flows occur more frequently throughout the park. The bedrock geology of Grand Canyon National Park provides an ideal location for the initiation of debris flows. The high relief combined with differential strength prop- erties of the rocks leads to a high potential for slope failures. The most common source of mobilized sediments for debris flows are the Hermit Shale and Esplanade Sandstone of the Supai Group. Other sources include the Kaibab Limestone, Toroweap Formation, and Coconino Sandstone; Muay Limestone and Bright Angel Shale; and Quaternary basalts in the western Grand Canyon. Disper- sive and swelling clays in some of these formations aid in the initiation of debris flows. The magnitude and frequency of debris flows control the hydraulics of the Colorado River in Grand Canyon National Park. Debris flows from the small tributaries aggrade fans that typically force the river against the opposite wall of the canyon. The ability of small drainages such as Monument Creek to form hydraulic controls (rapids) on one of the largest rivers in the United States is of great hydrologic significance. The debris fans also cause flow separation zones conducive to deposition and storage of sand on beaches, and reworking of debris fans by Colorado River discharges creates secondary riffles or rapids. Debris flows are the source of large volumes of sand entering the river at discrete points, although the debris flows occur infrequently. A thorough understand- ing of the magnitude and frequency of debris flows is of paramount importance to any understanding or long-term estimates of sediment transport in the Colorado River in Grand Canyon National Park. REFERENCES CITED Apmann, R.P., 1973, Estimating discharge from superelevation in bends: American Society of Civil Engineers, Journal of the Hydraulics Divi- sion, v. 99, p. 65-79. Beverage, J.P., and Culbertson, J.K., 1964, Hyperconcentrations of suspended sediment: American Society of Civil Engineers, Journal of the Hydraulics Division, v. 90, p. 117-126. Blackwelder, Eliot, 1928, Mudflow as a geologic agent in semiarid moun- tains: Geological Society of America Bulletin, v. 39, p. 465-494. Butler, Elmer, and Mundorff, J.C., 1970, Floods of December 1966 in southwestern Utah: U.S. Geological Survey Water-Supply Paper 1870-A, 40 p. 28 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA Chen, Cheng-lung, 1985, Hydraulic concepts in debris flow simulations, in Bowles, D.S., editor, Delineation of landslide, flash flood, and debris flow hazards in Utah: Logan, Utah, Utah Water Research Laboratory, General Series, UWRL/G-85/08, p. 236-259. Chow, V.T., 1959, Open-channel hydraulies: New York, McGraw-Hill, 680 p. Collins, R.O., and Nash, R., 1978, The big drops: San Francisco, Califor- nia, Sierra Club Books, 215 p. Cooley, M.E., Aldridge, B.N., and Euler, R.C., 1977, Effects of the catastrophic flood of December, 1966, North Rim area, eastern Grand Canyon, Arizona: U.S. Geological Survey Professional Paper 980, 43 p. Costa, J.E., 1984, Physical geomorphology of debris flows, in Costa, J.E., and Fleisher, P.J., editors, Developments and applications of geomorphology: Berlin, Springer-Verlag Publishing, p. 268-317. Costa, J.E., and Jarrett, R.D., 1981, Debris flows in small mountain stream channels of Colorado and their hydrologic implications: Bulletin of the Association of Engineering Geologists, v. 18, p. 309-322. Dolan, Robert, Howard, Alan, and Trimble, David, 1978, Structural con- trol of the rapids and pools of the Colorado River in the Grand Canyon: Science, v. 202, p. 629-631. Enos, Paul, 1977, Flow regimes in debris flow: Sedimentology, v. 24, p. 133-142. Fisher, R.V., 1983, Flow transformations in sediment gravity flows: Geology, v. 11, p. 278-274. Gallino, G.L., and Pierson, T.C., 1985, Polallie Creek debris flow and subsequent dam-break flood of 1980, East Fork Hood River basin, Oregon: U.S. Geological Survey Water-Supply Paper 22783, 22 p. Graf, W.L., 1979, Rapids in canyon rivers: Journal of Geology, v. 87, p. 538-551. Hamblin, W.K., and Rigby, J. K., 1968, Guidebook to the Colorado River, Part 1-Lees Ferry to Phantom Ranch in Grand Canyon National Park: Provo, Utah, Brigham Young University Geology Studies, v. 15, part 5, 84 p. Hooke, R.L., 1967, Processes on arid-region alluvial fans: Journal of Geology, v. 75, p. 438-460. Howard, Alan, and Dolan, Robert, 1981, Geomorphology of the Colorado River in Grand Canyon: Journal of Geology, v. 89, p. 269-297. Hungr, O., Morgan, G.C., and Kellerhals, Rolf, 1984, Quantitative analysis of debris torrent hazards for design of remedial measures: Canadian Geotechnical Journal, v. 21, p. 663-677. Huntoon, P. W., Billingsley, G.H., Jr., and Clark, M.D., 1981, Geologic map of the Hurricane Fault Zone and vicinity, western Grand Canyon, Arizona: Flagstaff, Arizona, Grand Canyon Natural History Association map, scale 1:48,000, 1 sheet. Huntoon, P.W., Billingsley, G.H., Jr., Breed, W.J., Sears, J.W., Ford, T.D., Clark, M.D., Babcock, R.S., and Brown, E.H., 1986, Geologic map of the eastern part of the Grand Canyon National Park, Arizona: Flagstaff, Arizona, Museum of Northern Arizona Special Publica- tion map, 1 sheet, scale 1:62,500. Hupp, C. R., 1984, Dendrogeomorphic evidence of debris flow frequen- cy and magnitude at Mount Shasta, California: Environmental Geology and Water Science, v. 6, p. 121-128. Johnson, A.M., and Rodine, J. R., 1984, Debris flow, in Brunsden, D., and Prior, D.B., editors, Slope instability: New York, John Wiley and Sons, p. 257-361. Kellerhals, Rolf, and Bray, D.I., 1971, Sampling procedures for coarse fluvial sediments: American Society of Civil Engineers, Journal of the Hydraulics Division, v. 97, p. 1165-1180. Kieffer, S.W., 1985, The 1983 hydraulic jump in Crystal Rapid- Implications for river-running and geomorphic evolution in the Grand Canyon: Journal of Geology, v. 93, p. 385-406. Laenen, Antonious, Scott, K.M., Costa, J.E., and Orzol, LL., 1987, Hydrologic hazards along Squaw Creek from a hypothetical failure of a glacial moraine impounding Carver Lake near Sisters, Oregon: U.S. Geological Survey Open-File Report 87-41, 48 p. Laursen, E.M., Ince, Simon, and Pollack, Jack, 1976, On sediment transport through the Grand Canyon, in Proceedings of the Third Inter-Agency Sedimentation Conference, Denver, Colorado, p. 4-76 to 4-87. Leopold, L.B., 1969, The rapids and pools-Grand Canyon, in The Colorado River Region and John Wesley Powell: U.S. Geological Survey Professional Paper 669, p. 131-145. McKee, E.D., 1969, Stratified rocks of the Grand Canyon, in The Colorado River Regions and John Wesley Powell: U.S. Geological Survey Professional Paper 669, p. 28-58. 1982, The Supai Group of Grand Canyon: U.S. Geological Survey Professional Paper 1173, 504 p. Pacific Southwest Inter-Agency Committee, 1968, Factors affecting sedi- ment yield and measures for the reduction of erosion and sediment yield: Pacific Southwest Inter-Agency Committee Report, 23 p. Pierson, T C., 1980, Erosion and deposition by debris flows at Mt Thomas, North Canterbury, New Zealand: Earth Surface Processes, v. 5, p. 227-247. 1981, Dominant particle support mechanisms in debris flows at Mt Thomas, New Zealand, and implications for flow mobility: Sedimentology, v. 28, p. 49-60. _____ 1985, Initiation and flow behavior of the 1980 Pine Creek and Muddy River lahars, Mount St.Helens, Washington: Geological Society of America Bulletin, v. 96, p. 1056-1069. Pierson, T.C., and Scott, K.M., 1985, Downstream dilution of a lahar- Transition from debris flow to hyperconcentrated streamflow: Water Resources Research, v. 21, p. 1511-1524. Piper, D.J. W., Farre, J. A., and Shor, A., 1985, Late Quaternary slumps and debris flows on the Scotian slope: Geological Society of America Bulletin, v. 96, p. 1508-1517. Postma, George, 1986, Classification for sediment gravity-flow deposits based on flow conditions during sedimentation: Geology, v. 14, p. 291-294. Potochnik, A.R., and Reynolds, S.J., 1986, Geology of side canyons of the Colorado, Grand Canyon National Park: Arizona Bureau of Geology and Mineral Technology Fieldnotes, v. 16, p. 1-8. Rogers, J.D., and Pyles, M.R., 1979, Evidence of catastrophic erosional events in the Grand Canyon of the Colorado River, Arizona, in Pro- ceedings of the 2nd Conference on Scientific Research in the National Parks, 26-30 November, San Francisco, California [reprint]. Schmidt, J.C., and Graf, J.B., 1988, Aggradation and degradation of alluvial sand deposits, 1965 to 1986, Colorado River, Grand Canyon National Park, Arizona: U.S. Geological Survey Open-File Report 87-555, 120 p. Scott, K.M., 1985, Lahars and lahar-runout flows in the Toutle-Cowlitz River system, Mount St. Helens, Washington-Origins, behavior, and sedimentology: U.S. Geological Survey Open-File Report 85-500, 202 p. Smith, G. A., 1986, Coarse-grained nonmarine volcaniclastic sediment- Terminology and depositional process: Geological Society of America Bulletin, v. 97, p. 1-10. Stevens, Larry, 1983, The Colorado River in Grand Canyon: Flagstaff, Arizona, Red Lake Books, 107 p. Taylor, R.E., Donahue, D.J., Zabel, TH., Damon, P.E., and Jull, A.J.T., 1984, Radiocarbon dating by particle accelerators-An archaeo- logical perspective: American Chemical Society Advances in Chemistry Series, no. 205, Archaeological Chemistry, v. III, p. 333-356. TABLES 1-12 30 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA TABLE 1.-Selected tributaries of the Colorado River, Grand Canyon National Park [X indicates that the attribute listed in the column heading was either observed or measured in the drainage.] Colorado Ancient Recent Strati- Events Tributary name River debris-flow debris-flow Faph analyzed mile deposits evidence graphy Y 19-Mile Canyon 19.0 X 24.5 Mile Canyon 24.5 X X X Shinumo Wash 29.2 X X Buck Farm Canyon 41.0 X X Unnamed canyon 43.3 X X Saddle Canyon 47.0 X Nankoweap Creek 52.2 X X Lava-Chuar Creek 65.5 X X X X Palisades Creek 65.7 X X Tanner Canyon 68.5 X Cardenas Creek 70.9 X X Unkar Creek 72.7 X 75-Mile Canyon 75.5 X X Red Canyon 76.8 X X Clear Creek 84 . 2 X X Bright Angel Creek 87.9 X Monument Creek 93.5 X X X X Crystal Creek 98.2 X X X X Shinumo Creek 108.6 X Elves Chasm 116.5 X X X Blacktail Canyon 120.2 X Forster Canyon 122.8 X Fossil Canyon 125.0 X X Unnamed canyon 127.6 X X Deer Creek 136.1 X Kanab Creek 143.5 X X Olo Canyon 145.7 X Matkatimiba Creek 148.0 X Havasu Creek 156.9 X X National Canyon 166.6 X X Fern Glen Canyon 167.9 X X Prospect Canyon 179.3 X X Parashant Wash 198.5 X X Fall Canyon 211.6 X X 220-Mile Canyon 220.0 X X Diamond Creek 225.8 X X iRiver miles are measured from Lees Ferry (Stevens, 1983). TABLES 1-12 31 TABLE 2.-Indirect-discharge calculation for the debris flow of 1966 on Lava-Chuar Creek, 0.2 mile upstream from the Colorado River SUPERELEVATION DATA Radius of curvature (RC) = 37 feet Channel width (W) = 110 feet Elevation difference (Abs) = 13.32 feet Channel slope (S) = 0.01 to 0.02 V = 12.0 feet per second (F = 1.0 to 1.4) CROSS SECTION DATA Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Section in feet feet in feet in feet Upstream 125 350 5.1 4.7 Superelevation 0 1,180 9.5 10.6 Downstream 250 310 3.2 3.3 Q = 4,000 cubic feet per second TABLE 3.-Indirect-discharge calculation for the debris flow of 1984 on Monument Creek at Tapeats Alcove, 1.5 miles upstream from the Colorado River SUPERELEVATION DATA Radius of curvature (Re) = 75 feet Channel width (W) = 79 feet Elevation difference (Abs) = 4.73 feet Channel slope (S) = 0.068 V = 12.0 feet per second (F = 0.6) RO ATA Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Sectio in feet feet in feet in feet Upstream 95 750 7.1 9.5 Superelevation 0 580 6.0 7.7 Downstream 50 320 6.0 7.4 Q = 4,000 cubic feet per second 32 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA TABLE 4.-Indirect-discharge calculations for the debris flow of 1984 on Monument Creek at site B, 0.5 mile upstream from the Colorado River SUPERELEVATION _ DATA Radius of curvature (RC) = 66 feet Channel width (W) = 65 feet Elevation difference (Ahs) = 3.73 feet Channel slope (S) = 0.065 feet V = 11.0 feet per second (F = 0.6) RUNUP_ DATA Elevation difference (Ahr) = 2.05 feet V = 11.5 feet per second (F = 0.6) S CTIO Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Section in feet feet in feet in feet Upstream 40 310 5.0 5.8 Superelevation 0 340 6.1 7.6 Downstream 18 420 5.2 6.2 Downstream 90 330 4.9 6.0 Average used 320 Q = 3,500 to 4,000 cubic feet per second TABLE 5.-Indirect-discharge calculation for the debris flow of 1984 on Monument Creek at site C, 0.3 mile upstream from the Colorado River SUPERELEVATION _ DATA Radius of curvature (Re) = 125 feet Width (W) = 97 or 106 feet Elevation difference (Ahs) = 3.41 or 4.57 feet Channel slope (S) = 0.063 V = 11.9 to 13.2 feet per second (F = 1.2 to 1.4) CROSS S ION DA Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Section in feet feet in feet in feet Downstream 45 320 3.4 3.8 Q = 3,800 to 4,200 cubic feet per second TABLES 1-12 33 TABLE 6.-Four scenarios of deposition on the Monument Creek debris fan used to calculate volumes of sediment deposited during the debris flow of 1984 SCENARIOS 1. Assume that debris flow did not reach the Colorado River and that the debris fan present in 1986 is the maximum deposition (unrealistically low). 2. Assume that the debris flow covered the fan and half of the Colorado River bed to a depth of 3 feet. 3. Assume that the debris flow covered the entire bed of the Colorado River to a depth of 3 feet (most realistic). 4 . Assume that the debris flow totally dammed the river to a depth of 11 feet (unrealistically high). FAN VOLUMES Fan River River Total Sand volume, area, River volume volume volume Duration in in depth, in in in of peak cubic square in cubic cubic cubic (Tp), in Scenario feet feet feet eet eet feet" seconds® 1 160,000 0 0 0 160,000 56,000 60 2 160,000 26,000 3 80,000 240 , 000 84,000 90 3 160,000 _ 49,000 3 150,000 310,000 110,000 120 4 160,000 _ 49,000 11 270,000 _ 430,000 150,000 160 'Average fan depth is an estimated 5 feet over a 32,000 feet?" area. 2The debris flow was approximately 35 percent sand. 3A total discharge of 3,800 and a sediment discharge of 2,700 ft3/s was used to estimate the duration of peak discharge. 34 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA TABLE 7.-Indirect-discharge calculation for the debris flow of 1966 on Dragon Creek at site E, 5.0 miles upstream from the Colorado River RUNUP_DATA Runup elevation (Mr) = 3.93 feet Channel slope (S) = 0.01 V = 15.9 feet per second (F =- 0.7) CTION T Area, in Hydraulic Hydraulic square radius , depth, Section feet in feet in feet Runup site 710 9.5 12.0 Q = 11,300 cubic feet per second TABLE 8.-Indirect-discharge calculation for the debris flow of 1966 on Dragon Creek at site F, 4.8 miles upstream from the Colorado River SUPERELEVATION _ DATA Radius of curvature (RC) = 75 feet Channel width (W) = 175 feet Elevation difference (AhS ) = 22.67 feet Channel slope (S) = 0.06 V = 17.7 feet per second (F = 1.3 to 2.7) CROSS SECTION DATA Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Section in feet feet in feet in feet Upstream #1 210 870 7.0 7.4 Upstream #2 90 670 3.9 3.6 Superelevation 0 2,480 12.5 14.2 Downstream 80 840 5.9 6.9 Average 790 Q = 14,000 (11,900 to 15,400) cubic feet per second TABLES 1-12 S5 TABLE 9.-Indirect-discharge calculations for the debris flow of 1966 on Crystal Creek at site G, 0.9 mile upstream from the Colorado River SUPERELEVATION DATA Radius of curvature (RC) = 132 feet Channel width (W) = 186 feet Elevation difference (Abs) = 4.65 feet Channel slope (S) = 0.04 V = 10.3 feet per second (F = 0.3 to 0.6) RUNUP_ DATA Elevation #1 (Aht) = 3.51 feet V = 15.0 feet per second (F = 0.6 to 1.2) Elevation #2 (Ahr) = 3.68 feet V = 15.4 feet per second (F = 0.6 to 1.2) CROSS SECTIO TA Thalweg distance from super- Area, in Hydraulic Hydraulic elevation, square radius , depth, Section in feet feet in feet in feet Upstream 135 940 5.6 5.9 Downstream #1 185 1,240 10.2 11.5 Downstream #2 255 890 9.7 11.9 Average 920 Q = 9,200 to 13,500 cubic feet per second TABLE 10. --Comparison of discharges calculated at all superelevation sites by the cross-sectional area at the highest superelevation marks and an average of the upstream and (or) downstream cross-sectional areas Mean Area at Dis- Average of Dis- velo- or near charge, upstream charge, - city, superele- in cubic and down- in cubic Location in feet vation, feet stream feet per in square per area, in per second feet second square feet second Lava-Chuar Creek 12.0 1,180 14, 200 330 4,000 at site F Monument Creek 12.0 580 7,000 320 3,800 at Tapeats Alcove Monument Creek 11.0 420 4 , 600 320 3,500 site B Monument Creek 11.9-13.2 000000 320 3, 800-4 , 200 site C Dragon Creek 17.7 2,480 43,900 790 14,000 site F Crystal Creek 10.3 1,240 12,800 920 9,500 site G DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA TABLE 11.-Historic flow events or channel changes in tributaries of the Colorado River in Grand Canyon National Park [Determination of changes is somewhat subjective. A confidence rating of 1 indicates a change or event occurred; a rating of 2 in- dicates that though a change or event probably occurred, the evidence is not strong; a rating of 3 indicates little confidence in the reported change. An (*) asterisk indicates a major change or event.] River Nature of Confidence mile side Tributary name event or change Year rating 7.0 L _ Unnamed chute Landslide 1970 1 7.8 R - Badger Creek Channel changes 1973-84 1 11.2 R - Soap Creek Channel changes 1935-65 2 11.2 R - Soap Creek Channel changes 1973-84 1 11.8 L - Salt Water Wash Channel changes 1935-65 2 11.8 L - Salt Water Wash Channel changes 1973-84 2 16.8 R - Rider Canyon Channel changes 1935-73 2 17.5 L 'Redneck Rapid' Rockfall 1978-79 1 26.8 R - 'MNA Rapid' Rockfall 1975 1 31.5 R - South Canyon Channel changes 1965-73 2 35.6 L - Unnamed channel Fan changes 1973-84 1 37.4 _L _- Tatahatso Wash Rockfall 1977 1 37.4 L - Tatahatso Wash Channel changes 1973-84 2 41.0 R - Buck Farm Wash Debris flow 1981-83 1 41.4 R - Bert's Canyon Channel changes 1973-84 2 43.1 L _ 43 mile camp canyon - Debris flow 1983 1 43.7 R - President Harding *Rapid formed 1911-23 1 43.7 L - President Harding Fan changes 1973-84 1 44.1 L _- Fan below Harding Fan changes 1983 1 44.5 L _- Fan below Harding Fan changes 1983 1 44.8 L _- Fan below Harding Fan changes 1983 1 52.0 R - Nankoweap Creek Channel shifted 1935-65 1 52.0 R - Nankoweap Creek Channel shifted 1966 1 52.0 R - Nankoweap Creek Channel shifted 1973-84 1 65.5 R - Lava Creek Debris flow 1966 1 65.5 R - Lava Creek Debris flow 1973-84 1 65.5 L - Palisades Creek *Debris flow 1965-73 1 65.5 L - Palisades Creek Channel changes 1973-84 2 66.3 R - Chute below Lava Cr - Fan changes 1965-84 1 66.3 L Chute below Palisade Channel changes 1965-73 2 66.9 L - Espejo Creek Fan changes 1973-84 1 67.2 L - Comanche Creek Fan changes 1973-84 1 67.9 L _ Unnamed drainage Fan changes 1965-84 1 68.1 L _ Unnamed drainage Fan changes 1965-73 2 69.6 R - Basalt Creek *Flood 1983 1 70.0 R - Unnamed drainage Fan changes 1973-85 1 70.2 R - Unnamed drainage Fan changes 1965-84 1 70.3 R - Unnamed drainage Fan changes 1965-84 1 70.4 L - Unnamed drainage Fan changes 1973-84 1 70.5 L - Unnamed drainage Fan changes 1973-84 1 70.8 L _ Unnamed drainage Fan changes 1973-84 1 70.9 R - Unnamed drainage Fan changes 1973-84 2 71.0 L - Cardenas Creek Channel changes 1984 1 71.2 R - Unnamed drainage Fan changes 1965-84 1 71.3 R - Unnamed drainage Debris flow 1983 1 71.8 R - Unnamed drainage Fan changes 1973-84 1 72.0 R - Unnamed drainage Rockfall, flood 1983 1 72.5 R - Unkar Creek Channel changes 1966 1 72.5 R - Unkar Creek Channel changes 1973-84 1 73.3 L - 6-8 small gullies Channel changes 1973-84 1 73.5 L - Unnamed drainage Fan changes 1965-84 2 73.7 R - Unnamed chute Fan changes 1973-84 1 73.8 R - Unnamed chute Fan changes 1973-84 1 74.4 R - Unnamed chute Fan changes 1965-84 2 74.9 L - Escalante Creek Fan changes 1973-84 1 76.8 L _- Red Canyon Channel changes 1973-84 2 87.8 R - Bright Angel Creek Large flood 1936 1 87.8 R - Bright Angel Creek - *Channel changes 1966 1 87.8 R - Bright Angel Creek Channel changes 1973-84 1 89.0 L - Pipe Creek Channel changes 1973-84 2 91.5 R Trinity Creek Flood or debris flow - 1985 1 92.2 L - Unnamed chute Channel changes 1973-84 2 92.8 L - Salt Creek Channel changes 1973-84 2 TABLES 1-12 TABLE 11.-Historic flow events or channel changes in tributaries of the Colorado River in Grand Canyon National Park-Continued River Nature of Confidence mile side Tributary name event or change Year rating 93.5 L - Monument Creek *Debris flow 1984 1 96.7 L - Boucher Creek Channel changes 1973-84 2 96.9 L Chute below Boucher - Channel changes 1973-84 3 98.2 R - Crystal Creek *Debris flow 1966 1 98.2 R - Crystal Creek Channel changes 1973-84 1 100.6 L _ Agate Creek Channel changes 1973-84 1 102.0 L - Turquoise Creek Channel changes 1973-84 2 108.6 R - Shinumo Creek Channel changes 1973-84 2 115.5 L - Unnamed canyon Channel changes 1985 1 116.5 L - Elves Chasm *Debris flow 1985 1 119.0 R - 119-Mile Creek Channel changes 1973-84 1 121.7 L - Unnamed chute Channel changes 1973-84 1 122.7 L - Forster Creek *Channel changes 1973-84 1 122.2 L - Unnamed chute Channel changes 1973-84 1 128.4 R - 128-Mile Creek Channel changes 1973-84 1 129.0 L - Spector Chasm Channel changes 1973-84 2 132.0 R - Stone Creek Channel changes 1973-84 2 132.0 L - Unnamed chute *New fan 1872-1968 1 133.8 R - Tapeats Creek *Debris flow 1961 1 133.8 R - Tapeats Creek Flood 1975 1 133.8 R - Tapeats Creek Flood 1984 1 136.2 R - Deer Creek Debris flow 1985 1 137.2 R - Unnamed chute Debris flow 1973-84 1 143.5 R - Kanab Creek *Large flood 1883 1 143.5 R - Kanab Creek *Large flood 1909 1 143.5 R - Kanab Creek Channel changes 1973-84 1 156.8 L - Havasu Creek *Large flood 1911 1 166.5 L - National Canyon Channel changes 1984 1 168.0 R - Fern Glen Canyon Channel changes 1973-84 2 174.2 R - Cove Canyon Channel changes 1973-84 1 176.4 R - Saddle Horse Canyon - Channel changes 1973-84 1 178.1 R - Unnamed chute Debris flow 1973-84 1 181.3 R - Unnamed chute Debris flow 1973 1 202.2 R - Unnamed canyon Debris flow 1973-84 2 202.3 R - Unnamed canyon Debris flow 1973-84 1 203.8 R - Unnamed canyon Debris flow 1973-84 3 204.1 L _- Unnamed canyon Channel changes 1973-84 2 205.2 L - 205-Mile Creek *Channel changes 1983 1 207.9 L - Unnamed canyon Channel changes 1973-84 3 209.0 R - Unnamed chute Rockfall 1978-79 1 211.5 R - Fall Canyon Channel changes 1973-84 1 220.0 R - 220-Mile Creek Channel changes 1984 1 225.8 L - Diamond Creek *Debris flow 1984 1 DEBRIS FLOWS FROM TRIBUTARIES OF THE COLORADO RIVER, ARIZONA TABLE 12.-Relation between difficulty rating for rapids and drainage area of the contributing tributaries for 67 rapids on the Colorado River [Rapid rating is a subjective scale from 1 (least severe) to 10 (most severe) based on navigational difficulty for oar-powered boats (Stevens, 1983)] Contributing area of 10,000 1921 Rapid name River drainages, cubic feet Water- surface mile in square per second fall, in feet miles rating Paria Riffle 0.9 1,410.0 1 2 Badger 7.9 46.6 6 12 Soap Creek 11.2 35.3 5 17 House Rock 16.9 308.6 7 9 North Canyon 20.5 154.1 5 12 21 Mile 21.1 0.3 5 5 Indian Dick 23.2 0.1 5 6 24.5 Mile 24.5 9.9 5 9 25 Mile 24.8 0.4 5 7 Cave Springs 25.2 0.7 5 6 Tiger Wash 26.7 19.8 4 7 29 Mile 29.2 60.8 2 6 Saddle Canyon 47.0 11.3 1 1 Nankoweap 52.2 32.6 3 25 Kwagunt 56.0 15.2 6 19 Little Colorado 61.5 26,955.0 1 8 Lava Creek 65.5 22.9 4 8 Basalt 69.2 5.3 3 2 Unkar 72.6 14.5 6 21 Nevills 75.5 4.6 6 15 Nance 76.8 4.1 9 26 Sockdolager 78.7 9.0 9 19 Grapevine 81.6 14.6 8 17 83 Mile 83.5 1.7 4 7 Clear Creek 84.1 35.7 1 2 Zoroaster 84.5 1.5 6 7 85 Mile 85.0 0.1 3 6 Bright Angel 87.9 101.0 4 8 Pipe Springs 88.9 6.6 4 14 Horn Creek 90.1 1.6 8 9 Salt Creek 92.6 1.2 4 3 Granite 93.5 3.3 9 17 94 Mile Creek 94 . 3 3.7 1 2 Hermit 95.0 12.6 9 15 Boucher 96.8 6.4 4 13 Crystal 98 . 2 47.9 10 17 Tuna Creek 99.2 23.3 6 10 Sapphire 101.3 3.7 7 7 Turquoise 102.0 5.7 4 2 104 Mile 103.9 1.7 6 3 Ruby 104.8 6.6 6 8 Serpentine 105.9 1.5 7 10 Bass 107.5 5.5 4 4 Shinumo Creek 108.5 85.5 4 8 Waltenberg 112.2 6.3 7 14 112.5 Mile 112.5 0.9 2 4 Rancid Tuna 113.0 0.5 6 4 Blacktail 120.1 9.3 3 7 122 Mile 121.8 3.1 5 4 Forster 122.8 3.9 6 7 Fossil 125.0 13.2 6 15 128 Mile 128.4 3.0 5 8 Specter 129.0 3.1 6 5 Bedrock 130.5 8.2 8 7 Deubendorf 131.8 7.3 8 15 Tapeats 133.8 82.9 6 7 134 Mile 134.3 2.2 3 7 135 Mile 134.9 1.8 5 2 Doris 137.7 0.3 6 2 Fishtail 139.0 7.7 6 10 Kanab Creek 143.5 2, 290.0 3 18 TABLES 1-12 TABLE 12.-Relation between difficulty rating for rapids and drainage area of the contributing tributaries for 67 rapids on the Colorado River-Continued Contributing area of 10,000 1921 Rapid name River drainages, cubic feet Water- surface mile in square per second fall, in feet miles rating Upset 149.8 30.9 8 15 Lava Falls 179.3 96.9 10 10 205 Mile 205.5 10.6 7 9 209 Mile 208 .8 88.3 7 12 L'il Bastard 212.1 0.2 3 5 217 Mile 217.3 9.2 7 13 GPO 685-041/9803 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur- rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." 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Los Angeles St. * MENLO PARK, California--Bldg. 3 (Stop 533), Rm. 3128, 345 Middlefield Rd. * RESTON, Virginia--503 National Center, Rm. 1C402, 12201 Sunrise Valley Dr. * SALT LAKE CITY, Utah--Federal Bldg., Rm. 8105, 125 South State St. * SAN FRANCISCO, California--Customhouse, Rm. 504, 555 Battery St. * SPOKANE, Washington--U.S. Courthouse, Rm. 678, West 920 Riverside Ave.. * ANCHORAGE, Alaska--Rm. 101, 4230 University Dr. * ANCHORAGE, Alaska--Federal Bldg, Rm. E-146, 701 C St. Maps Maps may be purchased over the counter at the U.S. Geologi- cal Survey offices where books are sold (all addresses in above list) and at the following Geological Survey offices: * ROLLA, Missouri--1400 Independence Rd. * DENVER, Colorado--Map Distribution, Bldg. 810, Federal Center * FAIRBANKS, Alaska--New Federal Bldg., 101 Twelfth Ave. Aggradation and Degradation of Alluvial Sand Deposits, 1965 to 1986, Colorado River, Grand Canyon National Park, Arizona By JOHN C. SCHMIDT and JULIA B. GRAF US: GEOLOGICAL SURVEY PROFESSIONAL PAPER 14953 Prepared in cooperation with the U.S. Bureau of Reclamation UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1990 DEPARTMENT OF THE INTERIOR MANUEL LUJAN, Jr., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging in Publication Data Schmidt, John C., 1950- Aggradation and degradation of alluvial sand deposits, 1965 to 1986, Colorado River, Grand Canyon National Park, Arizona / by John C. Schmidt and Julia B. Graf. cm.-(U.S. Geological Survey professional paper ; 1493) Includes bibliographical references. Supt. of Docs. no.: I 19.16:1493 1. Sand-Arizona-Grand Canyon National Park. 2. Sedimentation and deposition-Arizona-Grand Canyon National Park. 3. Alluvium-Arizona-Grand Canyon National Park. I. Graf, Julia B. II. Title. III. Series. QE471.2.835 1989 551.3'53'-de20 89-600263 CIP For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 CONTENTS Page Page Abstract 1 | Aggradation and degradation at Eighteen Mile Wash, Introduction 1 1965-86 Background 1 Topographic changes of the separation deposit ----------- 27 Purpose and scope 3 | Bathymetric surveys 31 Acknowledgments 4 | Aggradation and degradation of alluvial deposits, 1965-86 40 Terminology 4 Changes in alluvial sand deposits, 1973-84 40 Methods of analysis 4 Flow characteristics 40 Background 7T Changes in deposits 42 Physical and hydraulic characteristics of the channel ------ 7 Changes in alluvial sand deposits, high flows, May 1985 ---- 43 History of flow and sediment transport ---------------- 9 Flow characteristics 43 Characteristics and classification of alluvial sand deposits ------ 11 Changes in deposits 43 Separation deposits 14 Changes of alluvial sand deposits during strongly Reattachment deposits 19 fluctuating flow, October 1985 to January 1986 ------ 48 Upper-pool deposits 21 Flow characteristics 48 Channel-margin deposits 28 Changes in deposits 43 Distribution of deposits 28 Comparison of changes in alluvial sand deposits ---------- 46 Aggradation and degradation at Eighteen Mile Wash, Summary 47 1965-86 25 | References cited 48 Hydraulic conditions 25 | Appendix A-Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek --------------- 67 ILLUSTRATIONS Page FIGURE 1. Map showing study area and location of study sites 2 2. Graph showing instantaneous discharge at Lees Ferry gage, January 8-11, 1986, typical of fluctuating flows between 1965 and 1982 3 3. Diagrams showing flow patterns and configuration of bed deposits in a typical recirculation zone --------------------- 5 4. Map showing reaches within the study area 8 5. Map showing surficial geology and hydraulic features at Badger Creek Rapid 10 6-9. Graphs showing: 6. Change in length of recirculation zone with discharge at six sites 11 7. Typical particle-size distributions for samples of suspended sediment, bedload, and bed material from the Colorado River near Grand Canyon at river mile 87 and for two alluvial sand deposits -------------------- 12 8. Daily mean discharge of the Colorado River at Lees Ferry, 1957 13 9. Daily mean discharge of the Colorado River at Lees Ferry, 1982 to February 1986 13 10. Photograph showing separation deposits downstream from Badger Creek Rapid, July 30, 1985----------------------- 14 11. Map showing surficial geology and hydraulic features near Eighteen Mile Wash 15 12. Map showing topography of a separation deposit at Eighteen Mile Wash in 1975 and at selected times in 1985------------ 16 13. Cross section showing topography and sedimentology associated with upstream advancement of slipface, May 22, 1985, and August 2, 1985, at Eighteen Mile Wash 18 14. Aerial photograph and map showing surficial geology and hydraulic features at Eminence Break Camp----------------- 20 15. Maps showing bathymetric contours within the recirculation zone at Eminence Break Camp ------------------------ 22 16. Graphs showing bed-surface profiles of a recirculation zone at Eminence Break Camp - 24 17. Aerial photograph and map showing surficial geology, hydraulic features, area of sand inundated at different discharges, and sediment-sampling sites at Saddle Canyon 26 18. Photograph showing reattachment deposit at Eminence Break Camp, October 12, 1985, discharge 3,000 ft?/s =------------ 28 19. Sketch showing reattachment deposit at low discharge 29 20. Sketch showing response of a reattachment deposit to decreasing discharge 29 IH FIGURE 21. Sketch showing area of bathymetric surveys and hydraulic features at Blacktail Rapid TABLE 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. Ot > G0 ND + g ~ g 10. 12. 13. 14. . Summary of study sites and types of data collected . Characteristics of the reaches within the study area . Channel geometry and hydraulic characteristics for selected sites . Detailed study sites in relation to reaches . Particle-size characteristics of alluvial sand deposits between Lees Ferry at river mile 0 and Bright Angel Creek at river . Summary statistics of particle-size characteristics . Number of deposits that underwent change, 1973-84 CONTENTS Page Sketch showing bathymetric contours within a recirculation zone below Blacktail Rapid 29 30 Graphs showing bed-surface profiles of a recirculation zone below Blacktail Rapid 31 Sketch showing sedimentology exposed in a trench through the reattachment deposit at the site Above Cathedral Wash 32 Graphs showing variation with river mile in number of alluvial deposits identified in 1983 as campsites---------------- - 33 Aerial photographs showing Colorado River near Eighteen Mile Wash Sketch showing topography along profile 2 at Eighteen Mile Wash 34 35 36 Graph showing discharge and stage during recession 'of high flows at Eighteen Mile Wash Graph showing net-elevation change of separation deposit at Eighteen Mile Wash, 1965 to January 1986, along profile 2 37 Aerial photograph and map showing area of bathymetric survey, surficial geology, and hydraulic features at National Rapid Maps showing bathymetric contours within a recirculation zone below National Rapid 38 39 41 Graphs showing bed-surface profiles of a recirculation zone below National Rapid Graph showing vertical change along profile lines at 13 separation deposits between October 1985 and January 1986 ------ Graphs and map showing surficial geology and topography along two profiles at Twenty-Nine Mile Rapid -------------- TABLES - 44 - 45 Page mile 87.5 Areas of alluvial sand deposits at low discharge in selected reaches, October 1984 Summary of changes between bathymetric surveys Number of separation and reattachment deposits in recirculation zones between river miles 0 and 118, 1973 and 1984 ----- - 62 Areas of major alluvial sand deposits in selected reaches, 1973 and 1984 Classification of deposits studied by Howard (1975) and Beus and others (1985) Summary of measured changes at 20 sites during fluctuating flow, October 1985 to mid-January 1986 ----------------- Areas of exposed sand at detailed study sites, 1965, 1973, and 1984 - 64 CONVERSION FACTORS For readers who wish to convert measurements from the inch-pound system of units to the metric system of units, the conversion factors are listed below: Multiply inch-pound unit By To obtain metric unit foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) square foot (ft?) 0.0929 square meter (m*) cubic foot per second (ft/s) 0.02832 cubic meter per second (m*/s) ton (short) 0.9072 megagram (Mg) SEA LEVEL In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Sea Level Datum of 1929." AGGRADATION AND DEGRADATION OF ALLUVIAL SAND DEPOSITS, 1965 TO 1986, COLORADO RIVER, GRAND CANYON NATIONAL PARK, ARIZONA By Joun C. Scnmipnt and Jura B. Grar ABSTRACT Alluvial sand deposits along the Colorado River in Grand Canyon National Park are used as campsites and are substrate for vegetation. The largest and most numerous of these deposits are formed in zones of recirculating current that are created downstream from where the channel is constricted by debris fans at tributary mouths. Alluvial sand deposits are classified by location and form. Separation and reattach- ment deposits are downstream from constrictions within recirculation zones. Separation deposits are near the point of flow separation and typically mantle large debris fans. Reattachment deposits are near the point of flow reattachment and project upstream beneath much of the zone of recirculating current. Upper-pool deposits are upstream from a constriction and are associated with backwaters. Channel-margin deposits line the channel and have the form of terraces. Some are created in small recirculation zones. Reattachment and channel-margin deposits are largest and most numerous in wide reaches, although small channel-margin deposits are used as campsites in the narrow Muay Gorge. Separation deposits are more uniformly distributed throughout Grand Canyon National Park than are other types of deposits. In some narrow reaches where the number of alluvial sand deposits used as campsites is small, separation deposits are a high percentage of the total. During high flows, both separation and reattachment deposits are initially scoured but are subsequently redeposited during flow reces- sion. Sand is also exchanged between the main channel and recirculation zones. The rate of recession of high flows can affect the elevation of alluvial deposits that are left exposed after a flood has passed. Fluctuating flows that follow a period of steady discharge cause initial erosion of separation and reattachment deposits. A part of this eroded sand is transported to the main channel. Therefore, sand is exchanged between the main channel and recirculation zones and redistributed within recirculation zones over a broad range of discharges. Comparison of aerial photographs and reinterpretation of published data concerning changes of alluvial sand deposits following recession of high flows in 1983 and 1984 indicate that sand was eroded from recirculation zones in narrow reaches. In wide reaches, however, aggradation in recirculation zones may have occurred. In narrow reaches, the decrease of reattachment deposits was greater than that of separation deposits. In all reaches, the percentage of separation deposits that maintained a constant area was greater than for other deposits. Separation deposits, therefore, appear to be the most stable of the deposit types. Fluctuating flows between October 1985 and January 1986, which followed the higher and steadier flows of 1983 to 1985, caused erosion throughout the park. For separation deposits, erosion was greatest at those sites where deposition from the 1983 high flows had been greatest. The existing pattern of low campsite availability in narrow reaches and high campsite availability in wide reaches was thus accentuated by the sequence of flows between 1983 and 1985. INTRODUCTION BACKGROUND Alluvial sand deposits are used as campsites by back- packers and by about 15,000 persons who float the Colorado River in boats or rafts through Grand Canyon National Park each year. Sand deposits also are sub- strate for riparian vegetation. Flow in the Colorado River through Grand Canyon National Park has been regulated by Glen Canyon Dam since its completion in 1963 (fig. 1). From 1963 to 1982, regulation greatly decreased the range of discharges that occurred in any given year but greatly increased the range that occurred in a given day. The mean annual peak discharge of the Colorado River before flow regulation (1921-62) was 93,400 ft*/s (cubic feet per second); this decreased to about 29,200 ft*/s after regulation (1963-82). For most of 1965 through 1982, flow was regulated in direct response to electrical power demand. During a typical 24-hour period, the discharge range was large because power demand is high during daylight hours and low at night (fig. 2). Although flow through the powerplant at the dam could range from 1,000 to 31,500 ft°/s, discharge rarely varied over this entire range in a given day. A daily discharge range of 10,000 to 20,000 ft*/s was typical of the period. Unusually large releases of water that bypass the powerplant using river outlet works or both outlet works and spillways occurred in 1983, 1984, and 1985. In 1983, peak discharge at Lees Ferry (station 09380000, Colorado River at Lees Ferry, fig. 1) was 97,300 ft°/s. In 1984 and 1985, peak discharges at Lees Ferry were 58,200 and 47,900 ft*/s, respectively. Before construction of Glen Canyon Dam, the Colorado River carried a large suspended-sediment load through Grand Canyon National Park. All the sediment from the drainage area above the dam is now trapped in Lake Powell formed behind Glen Canyon Dam. Suspended- sediment samples collected at the gaging station at Lees Ferry between 1928 and 1959 commonly had concentra- tions that exceeded 10,000 ppm (parts per million). In 2 contrast, samples collected since dam construction typi- cally have concentrations less than 200 ppm. Concern was first raised in the mid-1970's that the combination of large daily discharge ranges typical of regulated flow and the loss of sediment supplied from areas upstream from the dam would cause a decrease in the size and number of alluvial sand deposits within the park. Laursen and others (1976) estimated both the capacity of the regulated river to transport sand and the amount of sediment supplied by tributaries below the dam. They predicted that sand deposits would eventually be depleted because transport capacity exceeded supply under regulated flow. Although Dolan and others (1974) suggested that widespread degradation of sand deposits might result from operations of the dam, Howard and Dolan (1981) found that sand deposits had "suffered only a very slight erosion." Howard and Dolan (1981) esti- AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA mated that alluvial sand deposits had reached equilibrium by the late 1970's, and they predicted little net change in the future. They stated, however, that erosion might occur if the characteristic pattern of dam releases of the 1970's were changed. On the basis of an inventory made after the high releases in 1983, Brian and Thomas (1984) concluded that a net loss of sand deposits large enough for use as campsites had taken place in the first 173 mi below Lees Ferry. They also concluded that a net increase in the same type of sand deposits had taken place farther downstream. Beus and others (1985) evaluated the his- tory of change of 20 major sand deposits between 1974 and 1984 by repeating topographic surveys first begun by Howard (1975). Beus and others (1985) concluded, "a substantial net gain of sand [due to high flows in 1983] * * * more than compensated for the previous 8-year loss." Tip - s as as s MK UTAH 112° a me =k hee me so me o e ~ s as (ge mpegs i [ 1 ARIZONA j h (| Cee gren Canyon as © Fredonia 'o -\ Dam p Lake Powell Cen Page a Lees Ferry t % so? o 3800 __ as 0 g & ARIZONA i 0% (6 s < o X e AL e (e #A § --© ~ J § i z mL AAS: -- AREATOF MAP 52 "ule ree ren reale r? =d 57V 13 AAA-o D & CC. .i! GRAND CANYON s _ (~- Z p A: I ® f-fk ''''' ke '. A C Q ide 4041.2 $7" g .s (i 0000 yx NATIONAL PARK |__ ._ (1 s COS, ) HWjSupai C fig f o ég Q 3831 N -d , T/ > "X; tC, $* * / sid ® 1" Ad & 0 & iz. § % ¥ 5 | a (r) a G 6/ % $ 4025 Q | * ® Grand Canyon 0 6 | 36° 2—3 u "C be- sme. * J 7 8 4 ® ”L__A1Desen View -I i é AL "E": a Bur ~» (40) < b / s) @ (20) (19) (is) Tile , Cameron &. ed 4042 %," $ % Cig O mong EXPLANATION m 0 10 20 30 MILES A3800 Gaging station and abbreviated number Cl Springs 0 10 20 30 KILOMETERS ® Study site listed in table 1 a C | | FIGURE 1. -Study area and location of study sites. INTRODUCTION 3 PURPOSE AND SCOPE The present study of alluvial sand deposits along the Colorado River began in 1984 in cooperation with the U.S. Bureau of Reclamation as one phase of a compre- hensive investigation of the effects of flow regulation on sediment transport in Grand Canyon National Park. The investigation was initiated in response to a U.S. Bureau of Reclamation proposal to increase peak powerplant discharges from 31,500 to 33,100 ft*/s. High discharges between 1983 and 1985 also provided an opportunity to investigate the effects of discharges that exceed power- plant capacity. Other phases of the overall study include: 1. Collection and analysis of flow and sediment-trans- port data at gaging stations (Graf, 1986; Pemberton and Randle, 1986); 2. Analysis of historical data from gaging stations (Burkham, 1986); 3. Mapping of channel-bed materials (Wilson, 1986); 4. Development and application of a sediment-transport model in the main channel (Orvis and Randle, 1986; Randle and Pemberton, 1987); and 5. Evaluation of sediment contributions from ungaged tributaries by debris flows (Webb and others, 1987). The results of this study will be integrated with results of other phases to determine the effect of flow regulation on sediment transport and storage in the Colorado River in Grand Canyon National Park. The study involved the evaluation of existing data and the collection of new data. Existing data consist mainly of aerial and ground photography (Laursen and Silverston, 1976; National Park Service, unpublished 1975 photo- graphs on file at Grand Canyon National Park; Turner and Karpiscak, 1980) and topographic surveys of deposits begun in 1974 (Howard, 1975; Beus and others, 1985; 25,000 20,000 15,000 10,000 5,000 DISCHARGE, IN CUBIC FEET PER SECOND | | I January 8 January 9 January 10 1986 January 11 FIGURE 2.-Instantaneous discharge at Lees Ferry gage, January 8-11, 1986, typical of fluctuating flows between 1965 and 1982. Ferrari, 1987). Data for this study were collected from May 1984 to February 1986. These data included meas- urements of flow velocity, scour-and-fill of sand deposits, topographic and bathymetric surveys, mapping surface- flow patterns, water-surface slope surveys, sedimento- logical analysis of some sand deposits, and replication of photographs. The study area extends from the gaging station (Col- orado River at Lees Ferry) at river mile 0 to the gaging station (station 09404200, Colorado River above Diamond Creek, at Peach Springs) at river mile 225 (fig. 1). Most of the fieldwork was done on raft trips beginning at Lees Ferry and ending at either Diamond Creek (river mile 225) or on Lake Mead (river mile 280). A helicopter was used to reach some sites on December 7 and 8, 1985, and on January 8 and 13, 1986. Forty-one study sites were selected as a representa- tive sample of different types of alluvial sand deposits used as campsites in most major reaches of the Colorado River corridor. The 41 sites and the types of data collected at them are summarized in table 1. The results of topographic and bathymetric surveys at 21 of these sites, referred to as detailed study sites, are discussed in this report. Bathymetric surveys were limited to reaches where a raft could be safely maneuvered and instruments could receive signals. In spite of the limitations, bathymetric surveys permitted mapping of large areas not otherwise accessible. Topographic surveying was limited to areas of safe wading; however, at low stages, large areas at some study sites could be mapped. Surface-current patterns and shorelines were mapped at two or more discharges. Surface velocities were estimated by timing floating objects and by using current meters. Bathymetric sur- veys were made at discharges between about 15,000 and 25,000 ft*/s (table 1). Other observations and surveys wgre made at discharges between about 3,000 and 45,000 ft*/s. The purpose of this report is (1) to present a classifi- cation of alluvial sand deposits in the Colorado River, (2) to describe significant characteristics of these deposits, (3) to describe changes in these deposits between June 1983 and January 1986, and (4) to relate these changes to those occurring since completion of the dam. The classi- fication of alluvial sand deposits and identification of 11 reaches within Grand Canyon National Park are pre- sented to provide a framework within which to evaluate changes in deposits. Description of the characteristics of alluvial sand deposits is included to substantiate the classification and to provide a basis for understanding change in spatial distribution of sand. Changes in alluvial deposits were identified by topographic and bathymetric surveys between April 1985 and January 1986 and by analysis of aerial photographs. 4 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA ACKNOWLEDGMENTS The fieldwork accomplished in this project was the direct result of the work of many individuals. Volunteers with the U.S. National Park Service or the U.S. Geolog- ical Survey included Bernard O. Bauer, James Harris, Robert Jacobsen, Catherine Hooper, Barbara Rusmore, and John Rusmore. Thanks go to them all as well as to the other field assistants. Dave Steinke made modifications to the equipment used for bathymetric surveys that made those surveys possible. Martha Hahn of the National Park Service arranged for the appointment of volunteers for the National Park Service and obtained unpublished data for our use. Boatmen for the raft trips were Jon Stoner, Stuart Reeder, Bob Grusy, and Owen Baynham; their skilled navigation and professionalism made all our work possible. TERMINOLOGY Flow separation and associated secondary circulations are characteristic hydraulic conditions in the Grand Canyon that determine sand-deposit location and extent of change. The phenomenon of flow separation at abrupt channel expansions or contractions is described in basic fluid mechanics texts. When flow separation occurs, the main downstream current becomes separated from the channel banks, and areas of recirculating flow exist between the downstream current and the banks (fig. 3). These recirculation zones are composed of one or more eddies, a term denoting "any rotating fluid motion which possesses continuity so long as the flow pattern which creates it continues to prevail" (Matthes, 1947). Eddies, as discussed in this report, have a vertical or nearly vertical axis of rotation. Typically, a recirculation zone has a primary eddy and may have a secondary eddy. That portion of the primary eddy where flow is directed upstream and toward the main downstream current is referred to as the primary-eddy return current. The bed of the recirculation zone excavated by this current is termed the primary-eddy return-current channel. Other portions of recirculation zones are not organized into a rotation. Currents in these low-velocity areas may have a preferential direction, may oscillate in several directions, or may be virtually stagnant. The point at which downstream-directed flow becomes detached from the channel banks is called the separation point (fig. 3A). The point at which downstream-directed flow is again adjacent to the banks is called the reattach- ment point. The separation point is the most upstream point and the reattachment point the most downstream point of the recirculation zone. On the Colorado River, these points are actually zones, 5-20 ft wide, within which the separation or reattachment point may migrate. A plane and its surface expression, the separation surface, divides the main downstream-directed flow from the recirculation zone. Two types of alluvial sand deposits within recirculation zones are highest in elevation and are of most interest to whitewater boaters and campers. Separation deposits mantle the downstream part of debris fans and are located near the separation point. Reattachment depos- its are located at the downstream end of recirculation zones, project upstream into the center of the zones, and are near the reattachment point (fig. 3B). At places, the surface of separation and reattachment deposits merge and the deposits cannot be distinguished solely on the basis of location, although they each have distinctive sedimentary characteristics. At other places, one or the other may not be found in a particular recirculation zone. Alluvial sand deposits are also typically located up- stream from constrictions. At least the lower part of many of these upper-pool deposits is a reattachment deposit associated with small recirculation zones. The higher parts of these same deposits, however, resemble terraces. Where the origin of alluvial deposits could not be determined on the basis of planimetric shape or location, they are called channel-margin deposits. Point-bar deposits, which are characteristic of alluvial meandering rivers, are uncommon in the park and are not discussed. Abrupt changes in flow area cause flow separation. In the Grand Canyon, the channel is typically more narrow and shallow around obstructing debris fans, and this short reach is called the constriction. Downstream from the debris fan, a short reach is wider than the average channel width and is called the expansion. Downstream from the expansion, the channel typically resumes the dimensions characteristic of the reach upstream from the constriction. The separation point typically is located near the transition from constriction to expansion. Re- circulation zones occur in the expansion. The ratio of channel width at the constriction to average width of the upstream channel is termed the constriction ratio. The ratio of channel width at the expansion to channel width at the constriction is termed the expansion ratio. The term elevation used in this report refers to the distance above or below either an arbitrary local datum or sea level. METHODS OF ANALYSIS Between April 1985 and February 1986, sand-deposit change was measured by repeated topographic and bathymetric surveys. These surveys, as well as photo- graphs taken between April and February, were com- pared with similar types of data collected between 1965 METHODS OF ANALYSIS Debris fan 4:1 "O.. aA Recirculation zone m ‘0.- 0. \ $ ffi} s Reattachment point 3. . QLow- /+: velocity area Separation point the #. E Separation CONSTRICTION EXPANSION Primary-eddy return-current channel Reattachment deposit Separation deposit Debris fanfi Upper-pool deposit ? '.. « I \ : i 4 ~ #4 & // le Channel-margin deposit # _-'-/_’l“ -" «ge // T4 f A4 | o P4 FIGURE 3. -Flow patterns and configuration of bed deposits in a typical recirculation zone. A, Flow patterns. B, Configuration of bed deposits. 6 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA and 1984 in order to measure change over longer time periods. Reference marks established by Howard (1975), Laursen and Silverston (1976), or Ferrari (1987) were used. At new study sites, networks of reference marks were established. A theodolite distance meter and standard techniques were used for most topographic surveys. About 25 percent of the topographic surveys were made using a hand level and tape. Surveys were made along profile lines, and topographic maps of most sites were made. Resurveys of reference-mark networks generally dif- fered by less than 0.10 ft from survey to survey. Surveying data were initially plotted in plan view to ensure that repeated surveys matched. Where they did not match, surveying data were adjusted for differences in position on the basis of surveying data of surrounding topography. This technique resulted in accurate depic- tion of topographic change along specific profile lines. Differences in elevation exceeding 0.25 ft are considered to be significant in this study. Bathymetric surveys were made from a raft about 35 ft long by using a recording echo-depth sounder and a local microwave positioning system. The positioning system consisted of two remote units mounted on tripods on shore, a master unit mounted on a mast on the raft, and the electronics that control their operation. The distance between the master and each remote is determined by the traveltime of microwaves. The position of the re- motes in the local coordinate system was determined by their location in relation to fixed reference marks, and the position of the raft at any time was computed from the known distances between the master unit and each remote. Data from the positioning system and the depth sounder were recorded along with time on a data logger as the raft moved about the study area. The time interval for recording could be changed but generally was 2 seconds. Depths were converted to elevation by refer- ence to elevation of the water surface during the survey. Maps of the data were plotted and contours were drawn by use of a computer-contouring system. Precision of the recordmg echo-depth sounder used is 0.1 ft, and accuracy is 0.5 percent of the measured depth or about 0.25 ft at a depth of 50 ft. Although maximum depth was 70 to 80 ft at a few study sites, maximum depth was less than 50 ft at most sites. Water-surface elevation during each survey was monitored either by a temporary recording-stage gage or by periodic reading of a staff gage on shore. Water-surface elevation changed with time during surveys and at a given time was different in different parts of the surveyed area. Change with time was caused primarily by discharge fluctuations or surface waves. During the bathymetric survey, the edge of water was mapped using standard surveying techniques. Depth changes in excess of 0.5 ft are considered significant. Spurious depths were recorded when air entrained in the water column caused the signal to reflect within the water column rather than off the channel bottom. Spuri- ous numbers in the data set, which were identified by comparing the stored numbers with depths recorded graphically, generally showed shallower depths than preceding or following measurements. In some places, entrained air severely limited the area that could be surveyed, especially downstream from rapids. Uncertainty of the distance measurement by each microwave unit is about 3 ft. Uncertainty of the raft position computed from the two distances depends mainly on the uncertainty of the distance measurement and on the relative positions of the master and remote units. Highest position accuracy (about 4.3 ft) is obtained when the master and remotes form a 90° angle. The accuracy decreases as the angle increases or decreases from 90° and is about 11.7 ft at angles of 30° and 150°. Remotes were located near the center of the recirculation zone or channel in such a way as to maintain a line of sight and to give as close to a 90° angle as possible over the survey area. The uncertainty of position ranges from the minimum of about 4.3 ft to about 20 ft. Data points from the positioning system were used to generate a grid of equally spaced values that were in turn used in graphical fitting of contours for computer plot- ting. Error of the grid was determined by computing the elevation at data locations by linear interpolation from the values at the grid nodes and comparing the calculated value with the measured value. The method of grid generation was selected to minimize interpolation error while maintaining a reasonable amount of smoothing of the data. Uncertainty in the position of contours also depended on the spatial distribution of data points. Where data points were sparse, contour position was extremely uncertain even though the interpolation error was low. The resulting uncertainty in the bathymetric maps is the sum of errors in microwave system location, com- puter contouring, and data-point density. The most significant of these is the uncertainty in raft position caused by poor geometry of the master and remote units and sparse distribution of data points. Although no quantitative measure of the map uncertainty was devel- oped, a qualitative judgment was made for each map, and areas judged to have uncertainty too great for meaning- ful analysis were omitted. Analysis of sand-deposit change at 13 detailed-study sites since 1965 relied mainly on photographic compari- sons. Aerial photography is available for 1965 (U.S. Geological Survey, scale about 1:15,000), 1973 (U.S. Geological Survey, seale about 1:7,200), and 1984 (U.S. Bureau of Reclamation, scale about 1:3,000). Daily mean discharge ranged from 23,100 to 41,200 ft*/s during the BACKGROUND 7T photographic survey of 1965, from 5,930 to 12,100 ft*/s during the survey of 1973, and from 5,220 to 5,810 ft*/s during the survey of 1984. Topographic changes at study sites were determined by measuring the area of exposed sand above the stage corresponding to a discharge of about 25,000 The area of exposed sand was directly measured in the photographs of 1965 for study sites where discharge was about 25,000 ft*/s. Estimates of the shoreline corresponding to a discharge of about 25,000 however, had to be made for the 1973 photography. The upper limit of unvegetated sand on the photographs of 1973 was determined to be associated with a stage of approximately 25,000 ft"/s by comparing topographic surveys and stage-discharge relations at Eighteen Mile Wash and opposite Nineteen Mile Canyon. Below this stage, sand was swept clean by daily fluctuations. The location of the shoreline at discharges of approximately 25,000 ft*/s was mapped in the field in August 1985 and drawn on 1984 photographs. A zoom transfer scope was used to adjust for differing scales of each aerial photo- graph survey. A planimeter was used to measure areas for different years, and differences in area of more than 10 percent were considered significant. Measurements of exposed sand deposits at a discharge of about 6,000 ft*/s were also made for 1973 and 1984 at about 180 sites. Measurements were made directly on aerial photographs. Accuracy of comparisons of exposed sand area is limited by the different seales of different aerial photographs as well as by the changing scale of each particular year's flight. For example, the ratio of scale difference between a unit area on the 1973 and 1984 photographs varied between 5.0 and 7.7, depending on location. In order to compensate for the errors resulting from varying scale, scale ratios were measured at about 1-mile intervals. Areas of deposits in 1973 were esti- mated by multiplying the area measured on the aerial photographs by the scale ratio so that comparison could be made with areas measured on the 1984 photographs. Areas in 1973 were estimated to be within a range determined by the highest and lowest seale ratios within about 10 mi of the measured site. Areas on 1984 aerial photographs were considered to be accurate to +10 percent. Significant change was considered to have occurred if the estimated 1973 area was entirely beyond the range of the 1984 area estimate. An inventory of the presence or absence of different types of alluvial sand deposits in 399 recirculation zones was also conducted between river miles 0 and 118 using 1973 and 1984 photography. Criteria used in this inven- tory are described in the section entitled "Changes in alluvial sand deposits, 1973-84." Other methods used to interpret or document topo- graphic changes or hydraulic conditions included scour chains, sedimentologic descriptions, water-surface slope surveys, and mapping of surface currents. Chains 2 ft long and having links of about 0.1 ft were inserted vertically into sand deposits along lines that were roughly perpendicular to shore. A metal detector was used to recover the chains; recovery was about 90 percent. Trenches were dug into sand deposits to reveal sedimentary structures. The size of trenches was limited by the time and equipment available. The largest trench was 80 ft long and 4 ft deep at Fern Glen Rapid. Surveys of water-surface slope were obtained by measuring the water-surface elevation at the edge of water. A staff gage was installed before each measure- ment, and observed fluctuations in stage were recorded. All surveyed points were located on aerial photographs along with the survey time. The water-surface survey was adjusted to compensate for measured stage changes. In order to decrease the length of time of the survey and therefore the stage changes during the survey, two rod persons usually were used. The direction of surface currents and location of shorelines were observed from the shore and mapped on aerial photographs. Uncertainty in position of features near the center of the channel is estimated to be about 5 percent of local river width. Noted features such as the location of separation and reattachment points along the shoreline are accurate to within 10 ft. BACKGROUND PHYSICAL AND HYDRAULIC CHARACTERISTICS OF THE CHANNEL The Colorado River channel is in bedrock or bordered by large talus blocks for most of the 225 mi from Lees Ferry to Diamond Creek. Geomorphic characteristics of the river channel are controlled by bedrock type and structure (Dolan and others, 1978). Channel width and depth, presence of midchannel gravel bars, and the distribution of tributary debris fans are all related to the bedrock geology (Howard and Dolan, 1981). Eleven reaches of the Colorado River were defined on the basis of type of bedrock exposed at river level, average channel top width, average channel width- to-depth ratio, reach slope, and relation to major tribu- taries (table 2; fig. 4). The narrow reaches are Upper Granite Gorge, Aisles, Middle Granite Gorge, Muay Gorge, Supai Gorge, Redwall Gorge, and Lower Granite Gorge. The wide reaches are the Permian Section, Lower Marble Canyon, Furnace Flats, and Lower Canyon. The elevation of the river decreases about 1,780 ft between Lees Ferry and Diamond Creek. The descent takes place primarily in short steep reaches, many of which are the famous rapids of the Grand Canyon. In the first 150 mi downstream from Lees Ferry, 50 percent of 8 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA the total decrease in elevation takes place in only about 9 | (Birdseye, 1923). Water-surface slope flattens in pools percent of the distance (Leopold, average gradient between Lees Creek is 0.0015, the gradient of exceeds 0.01. 1969). Although the | upstream from most major rapids, and mean velocity Ferry and Diamond | commonly is less than 3 ft/s. A deep scour hole is present many short reaches | immediately below most rapids (Leopold, 1969; Howard and Dolan, 1981; Wilson, 1986). Water-surface slope is low in reaches between rapids, Rapids are commonly located where the channel has and many reaches have a gradient of less than 0.0005 | been constricted by alluvial fans formed by debris-flow $ipe = N " MX UTAH__ a>. hks an ts s'... ks mt I ARIZONA T \_ Glen Canyon © Fredonia aria Dam lib, £35 Lees Ferry g (€ 380W - / : £3 0 § f ARIZONA X #3 8 X ~ 7 a g # S Js" N A $- A Q3. / "aA os "A$ 0 AREA OF MAP : _ ""~. _. cl 5 ves ~3 «f 8. 5 RAND. canyon o az" fx wk N ---___ 26) j {1 f.>,.40418 s (9) $5, aes @ € pS 7% ~~) NATIONAL PARK |_ 3 . ' 34 --f az $ '\l00\‘ // ) ¥ Supal @'v. T: 3831 \-\- fli—J // & “I $5 7 & if i ? ¢ s &Jf J % j I \){¥ J“; 4 a * A \,A,\' & O | f - 9 \ 4025 | / $s f'r I. O \ \A\ | y SJ { & ( \_ Grand Carlyon 0 o | /. 36° |-) (3 / "C *x "-' ___ Desen View 1," hus: wal NW / - 0 ~ - / {stii B & © Es % ”id!" A C T 2 a® Lifts n / / ,, Cameron & ® (6/0 4 1042 §f /" [% , Dig 0 ”Joqd 0 10 20 30 MILES Peach Spine 0 _ 10 _ 20 _ 30 KILOMETERS A € | | EXPLANATION (D Permian Section CD Aisles ® Supai Gorge Middle Granite Gorge (@) Redwall Gorge (@) Muav Gorge Q) Lower Marble Canyon Lower Canyon C5) Furnace Flats ® Lower Granite Gorge @ Upper Granite Gorge Agee, Gaging station and abbreviated number FIGURE 4. -Reaches within the study area. BACKGROUND 9 deposits at the mouths of short, steep tributaries (fig. 3). Debris from these flows also increases local bed elevation of the channel. Kieffer (1985) determined constriction ratios at 54 debris fans in the Grand Canyon, using 1973 aerial photography. She found that the ratio ranged from about 0.3 to about 0.7, and averaged about 0.5. Because discharge in the 1973 photographs ranged from about 4,000 to 15,000 ft*/s and constriction ratio might vary with discharge and stage, constriction ratios were recom- puted from 1984 photography. The mean constriction ratio at the same debris fans measured by Kieffer (1985) was 0.49, indicating that while individual sites might vary in relation to stage and method of measurement, when averaged over a number of sites, the effect of stage on constriction ratios is not significant. Because alluvial deposits large enough to be used as campsites are associated with small debris fans as well as the large fans measured by Kieffer (1985), constriction ratios were computed from 1984 photographs for 70 debris fans associated with alluvial deposits inventoried as campsites (Brian and Thomas, 1984) between river miles 0 and 61. The mean constriction ratio of these sites was 0.54, somewhat greater than that of the sample population of Kieffer (1985). The expansion ratio at the 70 sites ranged from 1.3 to 7.3, with a mean of 2.9. At 59 of these sites where channel-depth data (Wilson, 1986) are available, channel depth at the constriction decreased to as much as 0.30 of the upstream depth and increased in the expan- sion to as much as nine times the constriction depth. At most constrictions, recirculation zones exist at discharges between 4,000 and 45,000 ft*/s, but their sizes are not constant. At most sites, recirculation zones increase in length with increasing discharge at least to 45,000 ft*/s (Schmidt, 1986). At Badger Creek Rapid, the separation point is farther upstream and the reattach- ment point farther downstream at a discharge of 44,000 than at a discharge of 5,600 ft*/s (fig. 5). At extremely low flow, many recirculation zones are greatly reduced in size, and the bed of the recirculation zone may be completely exposed. For example, at Soap Creek Rapid, flow separation does not occur at discharges less than about 5,000 ft*/s. At each constriction, the debris fan is overtopped if the discharge is sufficiently high. As discharge increases above this overtopping discharge, the separation point does not migrate farther upstream. For example, over- topping occurs at the low fan at Eighteen Mile Wash between 28,000 and 44,000 ft*/s (fig. 6). At most sites, the downstream migration of the reattachment point is controlled by the geometry of the channel. Lengthening of the recirculation zone in the downstream direction is ultimately restricted where the downstream-migrating reattachment point encounters another riffle or debris fan farther downstream. An upper limit, therefore, exists on the length of recirculation zones, but the limit is different at different sites. Sand is stored primarily in main-channel pools and within recirculation zones (Wilson, 1986). Most sand deposits used as campsites are associated with recireu- lation zones and are formed at discharges typically exceeding 30,000 ft*/s. Sand stored within recirculation zones typically is very well sorted and fine to very fine grained (fig. 7, curve 7, 8), whereas sand in channel pools is typically medium grained (fig. 7, curve 5, 6). Channel geometry and hydraulic data based on field mapping of shorelines and currents at various discharges, water-surface slope surveys, and depth-sounder records were collected at 21 detailed study sites (table 3). The mean constriction ratio of these sites is 0.49 and is the same as the mean constriction ratio of the debris fans measured by Kieffer (1985) and less than the mean of 70 fans between river miles 0 and 61 discussed above. The 21 sites, therefore, are representative of more narrow constrictions than are associated with most campsites in the Grand Canyon. Study sites were concentrated in upstream reaches where the effects of dam operations were initially con- sidered to be most significant. Detailed study sites were located in seven reaches (table 4). Study sites in each of these reaches included the dominant types of deposits used for camping (table 2). HISTORY OF FLOW AND SEDIMENT TRANSPORT Two gaging stations provide long-term information on flow and sediment transport. The gage at Lees Ferry (fig. 1) was established in 1895, and in 1922, a gage (station 09402500, Colorado River near Grand Canyon) was established at river mile 87, just above Bright Angel Creek (fig. 1). Suspended-sediment samples were col- lected at the gage at Lees Ferry during the periods 1929-33, 1942-44, and 1947-65 and near Grand Canyon from 1925 to 1972. Sediment data also were collected at these two gages from June to December 1983 and from October 1985 through January 1986. Three additional gages were operated during the latter two periods. These short-term gages were at river mile 61, just above the confluence with the Little Colorado River (station 09383100, Colorado River above the Little Colorado River, near Desert View); at river mile 166, just above National Rapid (station 09404120, Colorado River above National Canyon, near Supai); and at river mile 225, just above Diamond Creek Rapid (fig. 1). Before closure of Glen Canyon Dam in March 1963, discharge at Lees Ferry typically reached its annual peak in June in response to snowmelt runoff from the upper basin. Smaller peaks occurred during the late summer and fall in response to rain in tributary watersheds 10 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA downstream from Lees Ferry (fig. 8). Suspended-sedi- Daily mean discharge of water for 1982 (fig. 9) was ment concentrations tended to be highest during these | typical of the period 1965-82. During that period, short- periods of tributary flow, and suspended sediment was | term discharge fluctuations dominated, and discharge dominated by silt- and clay-sized material (fig. 7, curve 2). | exceeded powerplant capacity of 31,500 ft*/s only in Badger Creek / (XE yz " o Ryn Mork ~ Roa SSS _> ~ ..'. Base from uncorrected aerial photography taken October 21, 1984 500 1000 FEET £ _" Arak c fe - f ed ad I I I I 150 300 METERS o--0 EXPLANATION RIVER DEPOSITED OR REWORKED GENERALIZED SURFACEFLOW DF- VERY FINE TO MEDIUM SAND RECTION IN RECIRCULATION (October 21, 1984) ZONES El EOLIAN SAND OR TERRACE DEPOS- Sn de tee Low flow ITS-Silt and fine sand, well sorted --» - High flow TRIBUTARY DEBRIS FAN-Boulders, cobbles, gravel, sand, poorly sorted; Q5 Surface-flow direction of main current boulders cover more than 50 percent p of surface area except in tributary LIMIT OF BREAKING WAVES (WHITE streambed P1 WATER) AT LOW FLOW-At high C flow, breaking waves in main current COBBLES AND GRAVEL extend downstream to a point oppo- TALUS AND BEDROCK site center of recirculation zones W ADDITIONAL - RIVER-DEPOSITED £353 _ DENSE STANDS OF TAMARISK 2d SAND (1973) SP SEPARATION POINT EDGE OF WATER =---= -- Low flow, October 5, 1985, 5,600 RP __ REATTACHMENT POINT cubic feet per second ©— LOCATION OF PROFILE LINES (Num- --- __ High flow, May 20, 1985, 44,000 cubic ber refers to table 13) feet per second IT PHOTOGRAPH STE-Figure 10 SEPARATION SURFACE -imeime* Low flow ' ------ High flow FIGURE 5. -Surficial geology and hydraulic features at Badger Creek Rapid. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS 11 April, May, and June 1965 and for a very short period in late June and early July 1980. Maximum instantaneous discharge at Lees Ferry was 60,200 ft*/s in 1965 and 44,800 ft°/s in 1980. Annual suspended-sediment load past Lees Ferry decreased from 76.3% 10° tons/yr in the period just before construction of the dam (1948 to 1958) to 8.6x10° tons/yr just after dam completion (1963 to 1965) (Laursen and others, 1976), which is a decrease of almost 90 percent. For the same periods, volume of water passing Lees Ferry decreased about 55 percent (Ander- son and White, 1979). The present study was planned and initiated in 1982 and early 1983, when flows such as those illustrated in figure 2 had prevailed for nearly 20 years. An exceptional combination of weather conditions and management decisions during the winter of 1982-83, however, caused subsequent flows to deviate from the previous regime (fig. 9). A record post-dam high instantaneous discharge of 97,300 passed Lees Ferry on June 29, 1983. From June 1983 until October 1, 1985, discharges were higher and steadier than ever experienced since closure of the dam. Discharges of as much as 46,000 ft*/s can 'be released without using the spillways; 31,500 ft*/s can be released through the powerplant and 14,500 ft*/s through river outlet works (David Wegner, U.S. Bureau of Reclamation, oral commun., 1986). The flat-topped hy- drographs of the summers of 1984 and 1985 (fig. 9) 2000 ; | l I 1800 |- - 1600 |- 1 s Lu i 1400 |- q z § *> . A Cami”, E woud - § | ~ — @ 1200 *** _- s t: t 4 f f 2 E wo}: /* t saddle Canyon _-. _ N '. _ sp ere: : el { <© p ol tane. “a ............ 3 y Creek R2". eal < soo |- gadget C:" T Cs — a A ............ s '“°__'—_--—-----__?--_-----l- ___________ 0 g yet Eighteen Mile Wash _ ws 600 |- ¥ / - ine e A 200 |- q 0 f j E I ; f os + 40 50 DISCHARGE , IN THOUSANDS OF CUBIC FEET PER SECOND FIGURE 6. -Change in length of recirculation zone with discharge at six ' sites. resulted from maximum releases through the river outlet works and powerplant. Discharges in June 1983 exceeded powerplant and outlet work capacity, and spillways were used. Only during a special fluctuating-flow study peri- od -October 1, 1985, to January 15, 1986-did releases resemble those characteristic of the 1965-82 period. The special fluctuating-flow study was planned and carried out for the purpose of providing a period in which to investigate the response of the river to typical power- plant releases. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS Fine-grained sediments are stored in channel pools, in recirculation zones, and in deposits that continuously line the wider sections of the river. Except for the widest reaches, most alluvial deposits are associated with the recirculation zones caused by minor bedrock or talus abutments or by large debris fans. In parts of the widest reaches of the Grand Canyon, terracelike deposits exist. Deposits associated with large recirculation zones are the most numerous and extensive alluvial sand deposits in Grand Canyon National Park. Side-scan sonar surveys, recording depth-sounder sur- veys (Wilson, 1986), and photography taken at low river stage demonstrate that the average bed elevation of recirculation zones is much higher than that of the adjacent channel. A pool or scour hole occurs immedi- ately downstream from the constriction. Adjacent to and downstream from this scour hole, the channel rises to the higher surface of a sandy alluvial deposit (fig. 3B). The upper surface of the sandy deposit typically has relief of 10 to 50 ft. The difference between the average bed elevation within a recirculation zone and the elevation of the adjacent thalweg varies from site to site. For example, at Blacktail Rapid, the elevation difference exceeds 80 ft, and at National Rapid and Eminence Break Camp, the elevation difference exceeds 40 ft. The separation and reattachment deposits associated with recirculation zones are composed primarily of me- dium to very fine sand. Between Lees Ferry and Bright Angel Creek, 22 deposits created since 1983 were sam- pled (table 5). Of the 55 samples taken at these deposits, only 4 contained less than 90 percent sand, and none of these samples contained more than 1 percent very coarse sand (greater than 1 mm). All samples of deposits between Lees Ferry and Bright Angel Creek that were inundated in 1983 or more recently have graphic means (Folk, 1968) between 0.095 and 0.39 mm. Of the 33 samples of deposits created by the discharges of 1983, 25 are fine sand and most are moderately well sorted. Fewer samples were collected of sediments deposited in 1984 and 1985, and half of these samples are medium sand between 0.25 and 0.50 mm. 12 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA WENTWORTH SIZE CLASS Very Very Silt fine Fine Medium Coarse coarse Granule Pebble I & l sand I sand I sand I sand I sand l | * 99.9 I r V ,. # 99.8 f- .,..l./|/,l " "il o 99.5 tts % 4 «- # - 99.0 .g 7/ s 98.0 f -< 95.0 «l RI 90.0 - w @ wl < o Fa ined < z F < S> 50.0 # b- CC -- u p-4 ira = |_. z --< u O CC ul & 10.0 walt 5.0 wel 1.0 wend 83 Ls t 0d | {2.3141 _| 1 -- 0.01 0.1 1.0 10.0 PARTICLE DIAMETER, IN MILLIMETERS EXPLANATION Discharge, Concentration, Curve Date Description in cubic feet in milligrams per second per liter 1 June 13, 1957 Pre-dam, snowmelt runoff 123,000 7,980 2 October 18, 1957 Pre-dam, tributary flow 15,600 17,000 3 October 22, 1983 Post-dam, no tributary flow 23,800 409 4 October 2, 1983 Post-dam, tributary flow 31,400 16,600 5 October 27, 1983 Bed material 6 December 18, 1985 Bedload 7 August 13, 1985 1983, reattachment deposit, Saddle Canyon 8 August 3, 1985 1985, separation deposit, Eighteen Mile Wash FIGURE 7. -Typical particle-size distributions for samples of suspended sediment, bedload, and bed material from the Colorado River near Grand Canyon at river mile 87 and for two alluvial sand deposits. DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND 140 120 100 40 20 100 80 CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS 13 JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC 1957 FIGURE 8. -Daily mean discharge of the Colorado River at Lees Ferry, 1957. Fluctuating flow k study a period Y 4 4 L 1 o WT Sup OLP L240. B LEL _L _E O4 coa F cd _L _L ___ _L _L_L AL_ L L. Look 4 c 4 f (ju _f 4 1 J F M A MJ J A S$ 0 N D|J F M A M J J A S 0 N D|J FMAMJJASONDJFMAMJJASONDIJF 1982 1983 1984 1985 1986 FIGURE 9. -Daily mean discharge of the Colorado River at Lees Ferry, 1982 to February 1986. 14 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA SEPARATION DEPOSITS Separation deposits mantle and typically extend down- stream from a debris fan. A zone of interspersed sand and boulders separates the separation deposit from the de- bris-flow deposits located upstream (fig. 10). The sepa- ration deposit generally forms one continuous gradual slope from crest to water's edge, but discrete terracelike levels may exist. The most upstream part of most of these deposits commonly does not border the low-flow river channel; boulders are found between the sand deposit and the water's edge (fig. 5). Downstream migration of separa- tion points with decreasing discharge probably causes erosion of sand in the upstream low-elevation portion of the separation deposit, resulting in this depositional pattern. Separation deposits form in low-velocity areas and in secondary eddies upstream from the primary-eddy re- turn-current channel. At some sites, a bar forms in a secondary eddy and the upstream-facing slipface of this deposit migrates upstream and eventually becomes at- tached to the debris fan. This process was observed at Eighteen Mile Wash, where a separation deposit (fig. 11) formed in a secondary eddy at a discharge of 45,000 ft*/s. At this discharge, the downstream part of the Eighteen Mile Wash debris fan was inundated. Velocity of this secondary eddy was much less than that of the main channel. Surface velocity through the riffle, at a dis- charge of 45,000 ft*/s on May 22, 1985, was measured to be about 16 ft/s on the basis of timing drifting boats. Mean velocities over the deposit in the low-velocity area at the same time did not exceed 1.5 ft/s (fig. 12B). Discharge over the deposit was about 160 ft*/s, which was only 0.4 percent of the main-channel discharge. The measured mean velocities at Eighteen Mile Wash are characteris- tics of velocities in low-velocity areas measured else- where. Sand transport in the low-velocity area at 45,000 ft*/s was upstream, away from the primary-eddy return current. Comparison of topographic surveys shows that approximately 13,000 ft" of very fine and fine sand was deposited between May 22 and the recession of high flows 33 days later. Aggradation occurred by upstream migra- FIGURE 10. -Separation deposits downstream from Badger Creek Rapid, July 30, 1985. Separation deposits mantle Badger Creek debris fan in foreground and Jackass Creek debris fan on opposite bank. Photograph site shown on figure 5. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS tion of the slipface (fig. 13) and by deposition on the downstream-facing slope. Sedimentary structures within the deposit consisted mainly of climbing ripples in the downstream part and planar foreset beds of the advance- ing slipface in the upstream part. If the measured volume change resulted from continuous deposition over the 33 days when the deposit was submerged, then the rate of deposition was about 390 ft°/d or about 0.03 vertical ft/d. It is possible, however, that deposition occurred more rapidly in only a small percentage of the total inundation period. The low discharge across the deposit and the fact that climbing ripples do not have supercritical angles of climb, however, suggest that the deposition was at a slow rate. Supercritically climbing ripples, in which all parts of 0 400 FEET 0 100 METERS / 15 the ripple surface are preserved, are associated with high sedimentation rates (Hunter, 1977). Comparison of currents at Eminence Break Camp (fig. 14) and bathymetric maps (fig. 15) and bed-surface profiles (fig. 16) for the high-elevation part of profile 2 between April and September 1985 also shows aggrada- tion in areas upstream from the primary-eddy return- current channel. The area was inundated by a secondary eddy and low-velocity area during the bathymetric sur- veys made at 26,000 and 27,200 ft*/s and during the high flows of May and June 1985. Separation deposits typically have a spit near the junction between the shoreline that faces the main current and the shoreline that faces the recirculation EXPLANATION RIVER-DEPOSITED OR REWORKED VERY FINE TO MEDIUM SAND (October 21, 1984) TRIBUTARY - DEBRIS FAN-Boulders, cobbles, gravel, sand, poorly sorted; boulders cover more than 50 percent of surface area except in tributary stream- bed // / / TALUS AND BEDROCK LOCATION OF SEPARATION POINT, 45,000 CUBIC FEET PER SECOND, MAY 22, 1985 LOCATION OF SEPARATION POINT, 28,000 CUBIC FEET PER SECOND, AUGUST 2, 1985 LOCATION OF SEPARATION POINT, 4,200 CUBIC FEET PER SECOND, OCTOBER 9, 1985 LOCATION OF REATTACHMENT POINT, 28,000 CUBIC FEET PER SECOND, AUGUST 2, 1985 O © O LOCATION OF REATTACHMENT POINT, 4,200 CUBIC FEET PER SECOND, OCTOBER 9, 1985 @- (€) rat oF MOVEMENT OF SEPARATION OR REATTACHMENT POINTS © --»» _ GENERALIZED SURFACE-FLOW DIREC- TION IN RECIRCULATION ZONES, 4,200 CUBIC FEET PER SECOND SURFACE-FLOW DIRECTION OF MAIN CURRENT, 4,200 CUBIC FEET PER SECOND -- -- -- APPROXIMATE LOCATION OF SEPARA- TION SURFACES, 4,200 CUBIC FEET PER SECOND Profile1- LOCATION OF PROFILE; SEE TABLE 13- Profiles 1 and 2 shown in figure 12 FIGURE 11. -Surficial geology and hydraulic features near Eighteen Mile Wash. 16 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA 4+ A A) °’/ ® d \\)°‘b o ,/1' Boulders Bedrock Boulders / 3 Bedrock 0 40 60 80 FEET Bedrock |L I I i 4 J 3 0 10 20 METERS EXPLANATION RIVER-DEPOSITED OR REWORKED VERY SURFACE-FLOW DIRECTION OF MAIN FINE TO MEDIUM SAND CURRENT - $5 -_ TOPOGRAPHIC CONTOUR-Elevations } } F - SLIPFACE OF RIPPLE related to arbitrary datum. Interval 1 foot --- _ SEPARATION SURFACE 1.1-» - DIRECTION AND MAGNITUDE (IN FEET £ ON SUSE: PER SECOND) OF MEAN VELOCITY a _ REFERENCE POINT FOR ARBITRARY ---» - GENERALIZED SURFACE-FLOW DIREC- DATUM-Elevation, 100 feet TION IN RECIRCULATION ZONES A-A" - LINE OF SECTION SHOWN IN FIGURE 13 FIGURE 12. -Topography of a separation deposit at Eighteen Mile Wash in 1975 and at selected times in 1985. A, July 7, 1975, on the basis of cross-section surveys (Howard, 1975) and ground photography. B, May 22, 1985, discharge 45,000 ft*/s. C, August 2, 1985, discharge 30,000 ft®/s. D, October 9, 1985, discharge 4,100 ft*/s. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS Boulders Bedrock Boulders \)°\6 Boulders W u FIGURE 12. -Continued +7 18 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA zone, such as the spit at Eminence Break Camp (fig. 14). Observations at National Rapid in June 1985 suggest that these spits form where sediment transported by a primary or secondary eddy is rapidly deposited into a low-velocity area. Separation deposits are not found downstream from all debris fans. For separation deposits to form, a stage- discharge relation and local topography must result in the existence of a low-velocity area and (or) secondary eddies upstream from the primary-eddy return current at some discharges. Debris fans with steep, high slopes do not typically have separation deposits because no discharges occur at which a low-velocity area or secondary eddy exists. At the study site Above Cathedral Wash, only discharges much greater than 100,000 ft*/s would overtop the constricting fan. Some fine sediments exist on the talus at elevations associated with floods in excess of 100,000 No low-elevation part of the separation deposit projects downstream, however, because the DOWNSTREAM A 100 - primary-eddy return current is adjacent to the talus at discharges less than 100,000 ft*/s. In contrast, at Emi- nence Break Camp, a large low-velocity area exists between the debris fan and the primary-eddy return current at discharges between 21,000 and at least 44,000 ft'/s (fig. 14, bottom). Mean velocities in this area at Eminence Break Camp were always less than 1.0 ft/s. At Saddle Canyon, separation deposits mantle the upper surface of the debris fan but do not project offshore. Low-velocity areas are present upstream from the pri- mary-eddy return current only at discharges above about 31,500 ft/s, and the separation deposit is confined to a small high-elevation area (fig. 17). Separation deposits may be subjected to significant wave action, particularly near steep rapids such as Nevills Rapid at river mile 75.5 and Granite Rapid at river mile 93.5. Howard and Dolan (1981) found that alluvial deposits had been reworked during approxi- mately 10 years of operation of Glen Canyon Dam. UPSTREAM A! ps a Elevation of water surface, Trench 3 May 22, 1985 [ -o % a“? E ust 2. 1985 z { May 22, 1985 _ _ _ pug! mereemc - t wane cane auc cmt c rm > 2 s. un 9 5 0 co < 90 ° 20 40 FEET IF I 0 10 METERS EXPLANATION WINDBLOWN SAND FINE TO VERY FINE SAND-Ripple crosslamination in wash, some planar lamination VERY FINE SAND—Comma); ripple crosslaminae and climbing ripples, grade offslope into organic-rich sand 3 FINE SAND-Steep foresets, disturbed upper surface, distinct avalanche laminae below, grades into "structureless" sand in wash below organic-rich sand of unit 4 2 FINE TO VERY FINE SAND-Planar foreset laminae and irregular distorted cross laminae in sets FINE TO VERY FINE SAND-Highly truncated ripple crosslaminae with organic lenses 0 RED SANDY GRAVEL-1984(?) flash flood deposit FIGURE 13. -Topography and sedimentology associated with upstream advancement of slipface, May 22, 1985, and August 2, 1985, at Eighteen Mile Wash. Location of section shown in figure 12. Descriptions by J.N. Moore, University of Montana, August 2, 1985. Vertical exaggeration 5x. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS 19 Adjustment to the different intensities of current and wave action that exist at different sites had occurred. For example, they found that where nearshore currents exceeded 1 ft/s or where swash runup exceeded 3 ft, parts of the deposit within the zone of fluctuating discharges had low gradients (approximately 3° to 9°) and were composed of medium sand (0.19 mm median grain size). Where nearshore currents and swash were less intense, the median grain size was less than 0.14 mm and gradients exceeded 10°. Sampling of deposits formed in 1983 or later does not demonstrate this kind of sorting. For example, some of the coarsest deposits reported by Lojko (1985) are at low-energy sites and some of the finest are at high-energy sites. The lack of sorting observed in deposits formed since 1983 is due to the fact that these primary fluvial deposits had not yet been subjected to fluctuating flows when they were sampled. Separation deposits may be finer grained than reat- tachment deposits. Graphic means (Folk, 1968) were calculated for each of 67 samples collected at 22 sites between Lees Ferry and Bright Angel Creek (table 6). The mean value of the graphic means of each of 12 samples of 7 separation deposits deposited after 1983 was 0.17 mm. A similar mean value was computed for 10 samples of 2 reattachment deposits; the sample mean was 0.25 mm. In terms of the total number of samples of these two deposits, the two sample means differ significantly at the 95-percent confidence level. The small number of sample sites, however, precludes definitive statistical conclusions. This difference between grain size of sepa- ration and reattachment deposits is spatially illustrated at Saddle Canyon. Three samples of separation deposits at elevations associated with discharges in excess of 45,000 had graphic means between 0.10 and 0.13 mm (fig. 17). Samples of reattachment deposits associated with discharges exceeding 25,000 ft*/s were all equal to or coarser than 0.15 mm. The grain-size difference between separation and reattachment deposits is related to the lower mean velocities associated with low-velocity areas, which are the depositional environment of separation deposits, in contrast with the higher mean velocities of reattachment point areas. REATTACHMENT DEPOSITS Reattachment deposits occur at the downstream end of many recirculation zones and project upstream as spits (fig. 3). A slipface typically exists along the shoreward side of the spit (fig. 18). The form of these deposits is well displayed in aerial photographs (fig. 14) taken at low discharges of about 6,000 ft*/s. These deposits were directly observed during clear-water flows at discharges of 30,000 and 45,000 ft*/s and were mapped during bathymetric surveys at discharges of 15,000 to 25,000 Although the deposits tend to move and adjust to changing discharge, the basic shape remains the same. Reattachment deposits form in primary eddies and build upstream from the reattachment point. Direct observations of surface-current patterns, migrating bed- forms, and bedform-migration directions exposed in trenches show that sand transport over most of these deposits is away from and perpendicular to the main current direction. Sand is transported across the top of the deposit, cascades down the slipface, and is swept upstream by the primary-eddy return current. Reattachment deposits fill recirculation zones to a varying extent. The low flows of October 1984 (fig. 9) exposed much of the bed of the recirculation zone at some locations (fig. 17), whereas at other locations, only a part of the deposit was exposed. Comparison of the area of reattachment deposit exposed at low discharge in 1973 with the area exposed in 1984 for selected sites shows that at sites where exposed area decreased, the decrease occurred in the upstream part of the deposit (fig. 19). Topographic and side-scan sonar data indicate that the decrease in exposed area is due to (1) loss of sand from recirculation zones and (2) redistribution of the same mass into a smaller area of higher relief. The topography of a typical reattachment deposit consists of a mound of sand or crest near the center of the deposit and a lower elevation extension of the crest downstream and onshore (fig. 18). A third area of higher elevation formed by high discharges may exist farther downstream. The higher parts of reattachment deposits typically extend the farthest downstream. This pattern is related to the hydraulic changes in recirculation zones that occur with decreasing discharge. Reattachment points typi- cally migrate downstream with increasing discharge and migrate upstream as discharge subsequently decreases (fig. 5). Therefore, alluvial deposits created at the highest discharges near the high-discharge reattachment point are abandoned by the recirculation zone as it decreases in size. Any downstream part of the sand deposit is subjected to downstream-directed flow, and eroded sand from these high banks is deposited in the main channel and not in the recirculation zone (fig. 20). Erosion or redistribution of sand upstream from the migrating reattachment point results in redistribution of sand within the recirculation zone and upstream migra- tion of the slipface. Fluctuating flows may result in further redistribution of sand within recirculation zones. The crest of a reattachment deposit formed under steady flows may be changed to a gently sloping continuous surface under fluctuating flows, such as occurred at Blacktail Rapid (figs. 21, 22, and 23). The farthest downstream part of the reattachment deposit nearly always degrades during fluctuating flows. For example, 20 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA Aerial photograph by U.S. Bureau of Reclamation October 21, 1984 0 100 200 300 400 FEET 100 METERS Reattachment® deposit FIGURE 14. -Surficial geology and hydraulic features at Eminence Break Camp. North is toward the top. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS 21 surveys at Blacktail Rapid (fig. 23, profile 1) and One Hundred and Twenty-Two Mile Creek showed significant bank retreat in this area between October 1985 and January 1986. § The effect of flow recession and recirculation zones that decrease in length on erosion of downstream parts of reattachment deposits was observed at Stone Creek where a steady discharge of about 40,000 decreased to about 35,000 ft°/s in June 1985. Overnight, a cutbank downstream from the new reattachment point retreated 2.75 to 3.5 ft and degraded about 1 ft. Two months later, the entire bar had been uniformly degraded to a new lower level. Substantial reworking of reattachment deposits may occur at high discharges. At the site Above Cathedral Wash, a truncated pre-1983 deposit was exposed in a trench, indicating that sand close to the river channel had been transported and redeposited since deposition of the older buried surface (fig. 24). Opposite Nineteen Mile Canyon, a similar buried pre-1983 surface was eroded but not entirely truncated. The existence of major truncation surfaces within reattachment deposits and the evidence that some reattachment deposits were significantly EXPLANATION RIVER-DEPOSITED OR REWORKED VERY FINE TO MEDIUM SAND (October 21, 1984) EOLIAN SAND OR TERRACE DEPOS- ITS-Silt and fine sand, well sorted TRIBUTARY DEBRIS FAN-Boulders, cobbles, gravel, sand, poorly sorted; boulders cover more than 50 percent of surface area except in tributary streambed COBBLES AND GRAVEL TALUS AND BEDROCK EDGE OF WATER-May 25, 1985, 41,000 cubic feet per second SEPARATION SURFACE-42,000 cubic feet per second GENERALIZED SURFACE-FLOW DIREC- TION IN RECIRCULATION ZONES- 41,000 cubic feet per second SURFACE-FLOW DIRECTION OF MAIN CURRENT SP SEPARATION POINT RP REATTACHMENT POINT Profile 1- LOCATION OF PROFILE LINES (Numbers refer to table 13) -) {s) & I [/// s FIGURE 14. -Continued eroded by the 1983 high flows (see section entitled "Aggradation and Degradation of Alluvial Sand Deposits, 1965-86") indicate that much of the sand in reattachment deposits is scoured, transported, and redeposited by high discharges. The form and sedimentology of reattachment deposits demonstrate that the final form is determined during flow recession. The discharge and sediment- transport characteristics of that recession, therefore, are important in determining the form and extent of the resulting deposit. Bedload samples were collected using a wadlng-type Helley-Smith sampler (Helley and Smith, 1971) in recir- culation zones below Kwagunt Rapid (river mile 56) and above the confluence with the Little Colorado River (river mile 60) (table 5). These sites generally are representative of recirculation zones at moderate dis- charges of about 28,000 ft°/s. Mean velocities probably were less than 2 ft/s where samples were collected. At both sites, the samples collected were well-sorted me- dium sand (mean value of samples 0.30 mm). Coarser sand, therefore, was in transport at a discharge of 28,000 ft*/s in the recirculation zones than is found in typical separation or reattachment deposits. This comparison suggests that separation and reattachment deposits can be redistributed in at least some recirculation zones at moderate discharges. Reattachment deposits tend to be coarser than sepa- ration deposits (table 6). Reattachment deposits may also coarsen with decreasing elevation at a site, such as at Saddle Canyon (fig. 17). Three samples of 1983 deposits at that site are fine sand (table 5, JCS-10, JCS-11, JBG-18) or medium sand (JBG-17). Samples from areas inundated by flows less than 25,000 ft*/s (table 5, JCS-6, JCS-7, JCS-8, JCS-9) are medium sand except for one sample (JCS-5) of a rippled veneer of very fine sand. This latter deposit is representative of mainstem deposition when tributaries are contributing sediment to the Colo- rado River. UPPER-POOL DEPOSITS Upper-pool deposits line the channel banks upstream from many debris-fan constrictions. The deposits are used as campsites where vegetation has been cleared or where tamarisk trees do not densely cover an area, such as above North Canyon Rapid at river mile 20.3 and above Crystal Rapid at river mile 98.0. In plan view, these deposits are linear and parallel to the channel, consist of different terrace levels, and typically have a low-elevation spit that projects into the channel in an upstream direction. Where spits exist, they are associ- ated with small recirculation zones upstream from a rapid and are formed by the same processes that form reat- tachment deposits. 22 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA High-elevation parts of upper-pool deposits probably are created by low-velocity downstream-directed over- bank flows. An example of an upper-pool deposit is the campsite upstream from Granite Rapid. This deposit is adjacent to the pool above the rapid. The plan-view form A of the deposit exposed at low flow includes a spit projecting upstream into the channel with a slipface on the shoreward side. At about 25,000 ft*/s this deposit is located at the downstream end of a recirculation zone. Higher exposures of sediment deposited during 1983 3 2 Z O ed D 3D m 2 ~4 So 6o 70 Edge of Water FIGURE 15. -Bathymetric contours within the recirculation zone at Eminence Break Camp. A, April 16, 1985, discharge 26,100 ft*/s. B, September 2, 1985, discharge 27,200 ft°/s. C, January 16, 1986, discharge 23,600 ft?/s. CHARACTERISTICS AND CLASSIFICATION OF ALLUVIAL SAND DEPOSITS 23 show that at least a part of the deposit was created by upstream-directed flows, which indicates that this recir- culation zone was larger at higher discharges. Upper-pool deposits may be subjected to erosive downstream-directed currents when the downstream constriction is overtopped. In August 1985, upper-pool deposits at Cathedral Wash at river mile 2.3 and Six Mile Wash at river mile 5.7 were examined briefly to deter- mine the effects of discharges of about 45,000 ft°/s. At each site, the upper-pool deposits had been eroded. CHANNEL-MARGIN DEPOSITS In some reaches, particularly where the channel is wide, sand deposits line the channel from a few hundred feet to nearly a mile. Channel-margin deposits are deposits that either lack the characteristic form of separation or reattachment deposits, or whose location in relation to recirculation zones was not known. Few C 0 0 EXPLANATION channel-margin deposits were investigated in detail; however, sedimentary structures within three such de- posits (left bank beneath the U.S. Geological Survey cableway above the Little Colorado River confluence, Above Grapevine Rapid at river mile 81.1, and Pumpkin Springs at river mile 212) indicate that the deposits were formed by recirculating currents. Typically, these depos- its mantle bedrock or talus. At low discharges, bedrock or talus may exist between the deposit and the water's edge. At other. locations, parts of the channel-margin deposit have the form of a reattachment deposit. At low discharge, these deposits are adjacent to the water's edge. DISTRIBUTION OF DEPOSITS Alluvial deposits large enough for use as campsites are most numerous between river miles 45 and 75, 115 and 140 (fig. 25), and 160 and 225. These areas are within 100 FEET 30 METERS --- 70 -- _ BATHYMETRIC CONTOUR-Hachures indicate depression. Elevations are related to an arbitrary local datum. Interval 10 and 2 feet ®_—— PROFILE LINE FIGURE 15. -Continued. 24 ELEVATION ABOVE AN ARBITRARY DATUM, IN FEET 80 70 60 50 40 90 80 170 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA T: I |- -| - - = - Profile 2 Profile 7 1 L L 1. 1 1 5 0 50 100 150 0 50 100 150 200 250 DISTANCE FROM POINT OF ORIGIN, IN FEET T T T + fi EXPLANATION e---e April 16, 1985 [~ 7 &---8 September 2, 1985 O---O _ January 16, 1986 |= y Profile 13 Te.. L L. 1 0 50 100 150 200 250 - DISTANCE FROM POINT OF ORIGIN, IN FEET FIGURE 16. -Bed-surface profiles (see figure 15 for locations) of a recirculation zone at Eminence Break Camp. AGGRADATION AND DEGRADATION ATEIGHTEEN MILE WASH, 1965-86 25 Lower Marble Canyon, Furnace Flats, Aisles, Middle Granite Gorge, and the Lower Canyon. These reaches include all those designated as wide (table 2) except the Permian Section, where availability of campsites is limited by dense tamarisk tree groves and not by small alluvial sand deposits. Although the Aisles and Middle Granite Gorge reaches are designated narrow, there is great variability in channel width in these reaches, and campsites are located in parts of the reaches with wide channels or large expansions. Measurements of the area of major alluvial sand deposits in seven reaches show that average deposit size is also largest in the widest reaches (table 7). At a discharge of 5,600 ft*/s, average campsite size was 60,000 ft? in Lower Marble Canyon but 8,200 its in the Muay Gorge. The smallest campsites are associ- ated with reaches where channel-margin deposits are the main type (table 2). The largest campsites in Lower Marble Canyon are large reattachment deposits exposed at low discharge. Channel-margin and separation depos- its are large in this reach as well. Campsites noted on figure 25 are those inventoried by Brian and Thomas (1984) and are listed in appendix A. The type of each deposit was determined by locating campsites on aerial photographs and comparing their form with the characteristic shapes of different types of deposits as described in this section. Observations of surface-current patterns at these sites aided in classify- ing some sites. The number of separation deposits ranges between 0.2 and 1.0 deposits per mile throughout most of the river (table 2). The number of separation deposits used as campsites does not increase in wide reaches, although total number of campsites increases (fig. 25). Average area of major separation deposits is greater in wide reaches and varies in seven reaches between 14,500 and 57,000 ft". As described above, local topography of debris fans is the most important determinant in the occurrence of separation deposits. These deposits form wherever local site conditions permit, regardless of reach charac- teristics. Channel-margin deposits are common in Lower Marble Canyon, Furnace Flats, and the Muay Gorge. At low discharges, these deposits have an average area of 73,000 ft" in Lower Marble Canyon but only 7,500 ft" in the Muay Gorge (table 7). The largest channel-margin de- posit in the Muay Gorge is 23,000 ft? (river mile 140.2). Campsites in Furnace Flats are similar in size to those of Lower Marble Canyon. Large campsites are typically associated with reattachment deposits and may be formed by similar processes. In Muay Gorge, channel- margin deposits typically mantle talus or bedrock in small reentrants. Reattachment deposits large enough to be used as campsites are numerous only between river miles 45 and 60 and between river miles 115 and 125. AGGRADATION AND DEGRADATION AT EIGHTEEN MILE WASH, 1965-86 At some sites, we have enough data to develop a history of aggradation and degradation from 1965 to 1986. The interpretation of data in the following section is illustrative of the interpretation of changes at other sites summarized in the section entitled "Aggradation and Degradation of Alluvial Sand Deposits, 1965-86." HYDRAULIC CONDITIONS A small separation deposit mantles the downstream part of a low debris fan at the mouth of Eighteen Mile Wash about 18.1 river miles downstream from Lees Ferry (fig. 11). About 15,000 ft" of sand was exposed at 5,600 ft"/s and covered about 30 percent of the Eighteen Mile Wash debris fan in October 1984. Boulders exposed along the edge of water at the base of much of the sand deposit at 2,500 ft"/s in October 1985 demonstrate that the sand deposit mantles the debris fan. The Colorado River flows through a riffle of only slightly steepened water slope as it flows around the debris fan. A slope of 0.002 to 0.003 over a 600- to 700-ft reach exists at discharges between 4,000 and 45,000 ft"/s. The reach has a total elevation drop of about 3 ft or about one-fifth the drop of major Grand Canyon rapids. A large, deep recirculation zone exists on the left side of the channel immediately below the riffle. Bathymetric sur- veys at a discharge of about 30,000 ft*/s indicated average water depths of 20 ft and a maximum depth of 37 ft in this zone. The deepest part of the nearby main channel is about 50 ft. The recirculation zone exists at all discharges between at least 2,500 and 45,000 ft*/s and extends in length by 35 percent as discharges increase from 3,000 to 45,000 ft*/s (fig. 6). Over this discharge range, the separation point is located on the downstream margin of the exposed boulder deposit and migrates downstream along the slope of the separation deposit as the discharges decrease below about 25,000 ft*/s (fig. 11). The location of the upstream part of the primary-eddy return current changes little with discharge. Stage changes are significant in this reach where the channel width-to-depth ratio is less than 10. Between 5,000 and 45,000 ft*/s, stage rises 20 ft; within the normal fluctuating flow range of 5,000 to 30,000 ft*/s, stage changes are about 14 ft. At the highest observed dis- charges (45,000 ft*/s), most of the Eighteen Mile Wash fan and the entire sand bar are submerged (fig. 12B). On May 22, 1985, at a discharge of 45,000 ft*/s, the entire deposit was submerged by a low-velocity area, as de- seribed in the previous section. Current directions and bedform migration at this discharge show that flow and sediment transport over the deposit was upstream. A 26 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA REATTAGHMEMD POIND Aerial photograph by U.S. Bureau of Reclamation October 21, 1984 FIGURE 17. -Surficial geology, hydraulic features, area of sand inundated at different discharges, and sediment-sampling sites at Saddle Canyon. AGGRADATION AND DEGRADATION ATEIGHTEEN MILE WASH, 1965-86 27 channel existed upstream from the slipface where flow was directed toward the main current. In August 1985, conditions in the recirculation zone were observed at a discharge of about 28,000 ft*/s. The primary eddy was in approximately the same location; however, the entire surface of the deposit was exposed (fig. 120). A small secondary eddy existed offshore from the downstream part of the deposit, and the mean velocities in this eddy did not exceed 1.2 ft/s. Elsewhere along the deposit face, measured mean velocities did not exceed 1 ft/s. TOPOGRAPHIC CHANGES OF THE SEPARATION DEPOSIT The first available aerial photograph showing topogra- phy of the deposit (fig. 26A) was taken May 14, 1965, at a daily mean discharge of about 26,700 ft"/s and at a stage of about 91 ft. Elevation of stage was estimated by comparison of shorelines in the 1965 photograph with mapping of the shoreline in 1985 at various discharges. EXPLANATION RIVER-DEPOSITED OR REWORKED FINE TO MEDIUM SAND-Inundated by discharges less than 22,000 cubic feet per second RIVER-DEPOSITED OR REWORKED VERY FINE TO MEDIUM SAND-Inundated by discharges between 22,000 and 48,500 cubic feet per second RIVER-DEPOSITED OR REWORKED VERY FINE TO FINE SAND-Inundated by discharges between 48,500 and 97,300 cubic feet per second EOLIAN SAND OR TERRACE DEPOSITS-Silt to fine sand, well sorted TRIBUTARY DEBRIS FAN-Boulders, cobbles, gravel, sand, poorly sorted; boulders cover more than 50 percent of surface area except in tributary stream- bed TALUS AND BEDROCK EDGE OF WATER-May 15, 1986, 48,500 cubic feet per second SEPARATION SURFACE-48,500 cubic feet per second GENERALIZED SURFACE-FLOW DIRECTION IN RE- CIRCULATION ZONES-48,500 cubic feet per second SURFACE-FLOW DIRECTION OF MAIN CURRENT SEDIMENT SAMPLE SITE, TABLE 5 -) [-) E § 1 - JCS-13 6 - JCS-10 2 - JCS-14 7 -IJBG-17, -18 3 -JCS-15 8 - JCS-11 4 - JCS-05, -06, -07 9 - JCS-12 5 - JCS-08, -09 10 - JBG-16 FIGURE 17. -Continued The shoreline along bedrock, talus, and the debris fan are very similar to the shoreline mapped in August 1985 at a discharge of about 28,000 ft/s. River stage in the photograph of 1965 was estimated by referring to the surveyed elevation of the water surface in August 1985. Sand exposed in the photograph of 1965 exceeds the elevation of the observed water surface and thus must be higher than 91 ft (fig. 27). In 1965, the deposit had an L-shape and bedrock was exposed between the deposit and water's edge at the downstream end. The part protruding toward the oppo- site bank may actually have been smaller than in 1985. A low area between the exposed debris fan and the sand deposit is believed to be a remnant return-flow channel. Better topographic control exists for the data of the mid-1970's. An aerial photograph was taken on June 16, 1973, at a discharge of about 4,500 ft*/s (fig. 26B). River stage was estimated to be about 78 ft. In the same year, photographs were taken from nearby cliffs accessible from the river, and on July 7, 1975, Howard (1975) surveyed the topography of the deposit along two pro- files. A topographic map of the deposit as it existed in 1975 was constructed from these data (fig. 124). The exposed fan and separation deposit in a photograph taken October 21, 1984, at a discharge of 5,600 ft*/s (fig. 26C) are similar in plan view to these deposits in 1973 and 1975. Data from the topographic survey of 1975, however, show that the shoreward part of the deposit was about 87 ft in elevation and that the sand surface rose to about 98 ft in elevation near the bedrock wall (fig. 27). A substantial part of this deposit, therefore, degraded at least 4.5 ft between 1965 and 1973. If the assumption is made that no change occurred in the estimated stage-to-discharge relation, this surface would be just overtopped by a discharge of 18,000 ft*/s. Between 1965 and 1973, maximum power- plant flows were about 24,000 ft*/s (Howard, 1975) or a stage of 89.5 ft, which is sufficient to inundate the main surface to a depth of about 2.5 ft. The air and ground photographs of the mid-1970's also document tamarisk trees at approximately a stage associated with flows of 24,000 The deposit was armored on all sides in 1973 (fig. 26B). After the flood of 1983, a resurvey of the deposit on September 13, 1983 (Beus and others, 1985), showed aggradation of about 6.5 ft on the stream side and about 4 ft of erosion of the high sand bank that had existed along the bedrock cliff (fig. 27). The elevation of the crest of the deposit was about 94 ft. Comparison of the discharge record of 1983 and the stage-to-discharge relation shows that the lowest discharge immediately before exposure of the deposit on August 10 was about 36,000 ft*/s (stage, 94 ft). This discharge had existed for about 8 days (fig. 284). At that time, the separation deposit was within 1 ft of this 28 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA stage. The river had been receding from its peak dis- charge of 97,300 ft°/s, which had occurred on June 29, 1983. A survey of the deposit on August 1, 1984 (Beus and others, 1985) (fig. 27), documented further aggradation of about 2 ft on the main surface to an elevation of about 96 ft. On the basis of the hydrograph of that year (fig. 9) and the local stage-to-discharge relation, the only flows that could have caused this aggradation were the high re- leases of May to July 1984, when daily mean discharge was about 45,000 ft*/s and stage was about 98 ft (fig. 28B). The bar aggraded to within 2 ft of the water surface. Although data are not available to date this aggradation more precisely, data collected in 1985 pro- vide an insight into deposit response during high flows. A resurvey of the deposit on May 22, 1985, showed that the deposit was much smaller than in 1984 (figs. 12B and 27). The river had been flowing between 38,000 and 46,000 since May 17, 1985 (fig. 9). Aside from a 6-day period when daily mean discharge was about 30,000 ft*/s, discharges exceeding 40,000 ft"/s continued until June 25 (fig. 28C). On the basis of the stage-to-discharge relation, the deposit would have been exposed on June 28 when discharges receded below 40,000 ft*/s. Resurveying on August 2, 1985 (figs. 12C and 27) showed that at least 2,900 ft" of sand, and more likely 13,000 ft?, had been deposited since the survey of May 22 despite the fact that the crest of the deposit had not increased in elevation. The latter estimate is based (1) on projection of surveyed slopes for unsurveyed areas by assuming the angle of repose and (2) on extension to known debris-fan deposits at depth. Analysis of sedimentary structures within this deposit showed that aggradation generally was consistent with directions of the current as measured in May. Steep planar foreset crossbeds document the upstream migra- tion of the deposit (fig. 13); however, the deposit also aggraded on its downstream-facing slope (fig. 27). Comparison of the surveys of August 1984 and May 1985, therefore, suggests that degradation is associated with the initial rise of discharge. This interpretation is reasonable despite the fact that from August 11 until August 15, 1984, spillway tests were run at Glen Canyon Dam and instantaneous peak discharges reached 56,600 ft"/s (fig. 9). Daily mean discharges exceeded 40,000 on three days. The extent of aggradation or degradation FIGURE 18. -Reattachment deposit at Eminence Break Camp, October 12, 1985, discharge 3,000 ft*/s. AGGRADATION AND DEGRADATION AT EIGHTEEN MILE WASH, 1965-86 29 on these days of high flow is not precisely known. However, the high flows likely resulted in only minor erosion at this site, because aerial photography for October 21, 1984 (fig. 26C) shows a deposit similar to that mapped earlier in 1984. The exposed deposit surveyed on August 2, 1985, was slightly smaller than at the time of the survey of August 1984 (fig. 27). The deposit may have been larger imme- diately after recession of the flows of 1984 than the same 2 yh Tf 06's y 15298°, 2°C "". (3% yobaogoo 2 ste, tim" ~ f 0°“ 0 Mee 2 5° 9:0. 0 / G C s # S s O2 vane 08 4 0.0.6 u 9%°¢~o ieeia®y.e de O s. p ena cranes: 2% react one EXPLANATION REATTACHMENT DEPOSIT DIRECTION OF FLOW NEAR REATTACHMENT DE- POSIT-Proportioned to volume of flow; largest arrows, greatest volume of flow FIGURE 19. -Reattachment deposit at low discharge. A and B, Pattern typical of the mid-1970's. C, Typical pattern following recession of high flows in 1984 and 1985; smaller area of exposed sand may be of higher elevation than larger exposed areas of the mid-1970's. deposit immediately after recession of the flows of 1985; however, erosion may have occurred in 1985 between the day of initial exposure, June 25, and the date of the survey, August 2. Thus, despite substantial scour of the x evQA *y wot #i e 1 at tt, on t E2 : ; ¢ ACs t as* Yas. 829 7 00 9 EQQO 8 -'.9C90flo,$,4>c39 Lt 20:55". 0.300». i rar one laa Pe € {5:30 8296, éPoQ'O'Q - 945-00 &. Net Ioweripgbhoug «* » transport to slipface y, 02320 s* *> ones s( s o f Le O+ 7 Slipf igration int ”0003 (25573éfot ipface migration into é _ "ROAR. S recirculation zone * m X ‘95‘250'foci & EEEEEH ‘Offlmraago" * ! gray an . ECH " :< 1/17. H W 0L &n + / QC C pell a A * 7, -" A Erosion to channel EXPLANATION «---» SURFACE-FLOW DIRECTION, HIGH FLOW RPH REATTACHMENT POINT, HIGH FLOW «--- «--* SURFACE-FLOW DIRECTION, LOW FLOW RPL REATTACHMENT POINT, LOW FLOW wee sa «« «* - EDGE OF REATTACHMENT DEPOSIT FIGURE 20.-Response of a reattachment deposit to decreasing dis- charge. Main o,, I‘re n Rapid t 0 100 200 300 400 FEET form. inch 0 100 METERS EXPLANATION _ _ LOCATION OF SEPARATION SURFACE, 20,000 TC. CUBIC FEET PER SECOND, AUGUST 12, 1985 GENERALIZED SURFACE-FLOW DIRECTION IN RECIRCULATION ZONE, 20,000 CUBIC FEET PER SECOND AREA OF BATHYMETRIC SURVEYS FIGURE 21. -Area of bathymetric surveys and hydraulic features at Blacktail Rapid. --> 30 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA deposit during the 1985 flood, the deposit likely never aggraded higher than 1 to 2 ft below the water surface in 1984 or 1985. Each year, the deposit was reestablished in approximately its same shape. In each of these years, the 0 100 FEET 0 30 METERS EXPLANATION --2086-- BATHYMETRIC CONTOUR-Hachures indicate depression. Elevations are related to National Geodetic Vertical Datum of 1929. Interval 10 and 2 feet (: > PROFILE LINE FIGURE 22. -Bathymetric contours within a recirculation zone below Blacktail Rapid. A, September 7, 1985, discharge 22,600 ft*/s. B, January 24, 1986, discharge 20,100 ft*/s. flow receded in a similar pattern. In 1983, aggradation was well documented, but the resulting deposit was of lower elevation. The deposit was reworked by flows of 36,000 during flow recession. At that discharge, the deposit would also have been about 1 ft below water surface. The level to which the deposit typically restabi- lizes after initial scour may be a direct function of the rate of decrease in discharge during flow recession. Net aggradation between 1983 and 1984 probably does not reflect greater sediment transport during the latter event, although sediment-transport data are not avail- able to document main-channel conditions. Local geome- try of the Eighteen Mile Wash debris fan is such that between 36,000 and 28,000 ft*/s, flow is diverted away from the separation deposit. Therefore, in 1984, separa- tion-deposit elevation was related to the 45,000 ft*/s discharge, but in 1983 the deposit continued to be reworked until discharge dropped from 36,000 to 25,000 In each case, equilibrium conditions limit aggrada- tion to about 1-2 ft below the water surface in the low-velocity area. After October 1, 1985, discharge never exceeded 20,000 ft*/s or a stage of 88 ft during this study. Stage was sometimes as low as 76 ft. During this time, the down- stream part of the deposit eroded rapidly (fig. 27). In January 1986, after 3 months of fluctuating flow, a 3-ft-high cutbank still existed. It had retreated horizon- tally 15 to 25 ft between August and early January. All erosion between October and January can be attributed to strongly fluctuating flow, and at least part of the erosion from August to October probably is associated with the first few days of fluctuating flows before the survey in October. The base of the cutbank developed at the approximate elevation of the highest discharge of the fluctuations from October to mid-January. Most of the retreat, therefore, was caused by bank collapse from saturation and undermining of the well-sorted fine sand. Nearshore velocities did not exceed about 1 ft/s. Waves were not present at this site. Degradation of the slope below the cutbank, subject to daily discharge fluctua- tions, was at a lower rate than degradation of the high exposed cuthbank. Aggradation caused by the high releases of 1983 more than compensated for the erosion that had occurred between 1965 and 1975 (fig. 29). Data are not available for 1975-83. Howard and Dolan (1981), however, observed that alluvial deposits had stabilized by the late 1970's. The alternating pattern of aggradation and degradation between June 1983 and May 1985 related to annual high flows is estimated on the basis of measured erosion and deposition during high releases in 1985 described above. The amount of degradation between August 1985 and January 1986 is similar to the net change between 1965 and 1975. The rate of change measured in 1985 and 1986 BATHYMET far exceeds the average rate for the earlier period. The existence of a cutbank at the end of the special fluctuat- ing-flow period suggests that erosion would have contin- ued if strong fluctuations had continued beyond mid- January. Therefore, at this site, newly aggraded deposits formed and reworked by flows in 1983, 1984, and 1985 were unstable under strongly fluctuating discharge. Upslope projection of the lower part of the January 1986 profile gives a likely minimum erosion that would have occurred if fluctuations had continued. A likely maximum extent of erosion would be degradation to the profile surveyed in 1975. BATHYMETRIC SURVEYS Short-term topographic changes in recirculation zones were measured by repetitive bathymetric surveys. The time of day and discharge during each survey are listed in table 1. Because these surveys are primarily of the lower elevation parts of recirculation zones, surveyed areas are not used as campsites; however, they are the major sand storage sites in recirculation zones. 2090 1 5 2090 2080 |- - 2080 2070 |- { 2070 i— rc Profile 1 LL Z 2060 1 { 2009 z 150 100 50 0 o i- <4 a 2050 _J LJ 2090 T T T 2040 2080 |- -4 2030 Profile 8 2070 L L 1 200 150 100 50 0 DISTANCE FROM POINT OF ORIGIN, IN FEET RIC SURVEYS 31 The recirculation zone at river mile 120.1 just below Blacktail Rapid was surveyed with 710 data points in September 1985 and January 1986 (table 1). The zone is nearly circular in plan view (fig. 21). The primary eddy covers most of the area, although small secondary eddies were observed along the banks during both surveys. The zone has an excellent geometry for bathymetric survey- ing. Uncertainty in position is less than 5 ft over most of the area but reaches almost 18 ft at the extreme downstream end of the surveyed area. The bathymetric map of September (fig. 224) illus- trates the characteristic shape of the sand deposit within the recirculation zone. The sand deposit had a relatively level upper surface and a steep slope into the main channel. A reattachment deposit and primary-eddy re- turn-current channel were present on the upper surface. A small separation deposit was present at the upper end of the zone upstream from the return-current channel but was a minor part of the total zone. A bathymetric map based on the January survey shows that considerable changes had taken place in these features (fig. 22B). Volume changes estimated for this recirculation zone by comparison of bathymetric maps represent change in a----a September 7, 1985 o----o - January 24, 1986 Profile 4 p=" I N 1 | 250 200 150 100 50 0 DISTANCE FROM POINT OF ORIGIN, IN FEET FIGURE 23. -Bed-surface profiles (see figure 22 for locations) of a recirculation zone below Blacktail Rapid. 32 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA volume of sand below the stage corresponding to the discharge at the time of the surveys. Discharge was strongly fluctuating for most of the period between the surveys, but fluctuated less strongly (15,000-21,000 ft/s) for the eight days before the January survey. Therefore, the observed changes may not be solely related to the effects of strongly fluctuating flow. The return-current channel was shallower and less well developed during both surveys at this site than in other surveyed recirculation zones, and it was shallower and less distinct in January than in September. The elevation of much of the reattachment deposit was 2-4 ft lower in January than in September, and the slope had flattened and moved toward the channel thalweg. Profiles drawn from bathymetric maps illustrate and quantify these changes (fig. 23). Profiles 1, 4, and 8 show how changes varied over the zone. The extreme downstream end of the zone (profile 1, fig. 23) and most of the crest of the 75 T T ~T T T I Discharge at indicated stage, in cubic feet per second 70 44,000 65 |- 60 |- ELEVATION, IN FEET ABOVE AN ARBITRARY DATUM 55 1 1 1 1 1 L u 5 10 15 20 25 30 DISTANCE FROM INITIAL POINT, IN FEET EXPLANATION 5 FINE TO MEDIUM SAND-Current ripples that migrate upstream on foresets that dip toward river, amplitude of current ripples decreases upslope 4 FINE SAND-Current ripples, current direction upstream away from main channel 3 INTERBEDDED FINE SAND AND SILT-Unit dips at low angle away from main channel or in downstream direction. Entire unit grades upward into unit 4 va FINE SAND-Generally massive with abundant roots and organic debris, includes an organic-rich lens that dips toward main channel. Laminae above the lens is contorted. Entire unit grades upward into unit 3 and pinches out 17 feet from initial point 1 BLACK AND GRAY CLAYEY AND SILTY FINE SAND-Layers of sand define irregular bedding, upper contact is erosional and includes a vertical cutbank 33 feet from initial point. Interpreted to be pre-1983 deposit 35 FIGURE 24. -Sedimentology exposed in a trench through the reattachment deposit at the site Above Cathedral Wash. Descriptions by T.R. Clifton, University of California, Santa Cruz, January 9, 1986. BATHYMETRIC SURVEYS 33 reattachment deposit degraded, whereas the slope into the main channel aggraded (profile 4, fig. 23). At the upstream end, aggradation on the downstream side of the return-current channel caused the channel to shift to- ward the bank and to become shallower (profile 8, fig. 23). On all profiles, the point of zero change is roughly coincident with the break in slope between the upper surface of the sand deposit and the slope into the main channel. In January the sand deposit sloped uniformly and gently toward the main channel and did not have a distinct reattachment-deposit crest and primary-eddy return-current channel. The amount of change between the two surveys was estimated by measuring the area between profile lines for successive surveys (fig. 23, table 8). Along all profiles, degradation totaled 1,100 ft2 and aggradation totaled 3,010 ft". Net change was 1,910 ft" of aggradation. Vertical change along profiles was estimated by dividing the area of change by the length of the profile. An average of 1-2 ft of degradation occurred over the upper CHARACTERISTIC WIDTH OF REACH wide | _ narrow _ | WIDE | NARROW * St -free -F-" TSST F- GR+-+-tt-+*-*+~+~+ A EXPLANATION 20 |- *---® Total deposits 7 15 10 &----a Separation deposits . » / NUMBER OF DEPOSITS WITHIN 5 MILES DOWNSTREAM OF INDICATED RIVER MILE SF- -~ To LI f TCT o CT OCO f Ct -T TT] B EXPLANATION 10 |- © Reattachment deposits x-:-X Channel-margin deposits 0 . 5 - % (¢: i . B psi ééfil'~.é4.4.é 8 -. 1... 1. pero _L Td 3. ._ fed 50 75 100 125 150 160 RIVER MILE FIGURE 25. - Variation with river mile in number of alluvial deposits identified in 1983 (Brian and Thomas, 1984) as campsites. A, Total number of deposits and number of separation deposits. B, Number of reattachment deposits and channel-margin deposits between Lees Ferry and National Rapid. 34 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA FigurE 26.-Colorado River near Eighteen Mile Wash. A, May 14, 1965, discharge 26,700 B, June 16, 1973, discharge 4,500 ft*/s. C, Oc- tober 21, 1984, discharge 5,600 ft/s (U.S. Bureau of Reclamation _ photograph). Surficial geology is shown on figure 11. BATHYMETRIC SURVEYS surface of the deposit, and aggradation of 3-6 ft occurred along the slope into the main channel. Areas of change along profile lines were used to estimate volume of change over the mapped area by 35 assuming that changes computed at profile lines took place over half the distance between a profile line and the adjacent line. For profiles 1 and 8 at the upstream and downstream ends of the area, only the area on the side of 100 T T T 752/on ;o lZ. ”a“- Bu ELEVATION, IN FEET ABOVE AN ARBITRARY DATUM 78 |- L 1 L | 'm ~T T T 50 Upper limit of river outlet works and power plant discharge 7 t & Upper limit of power plant discharge t 8 Il No o DISCHARGE AT INDICATED STAGE, IN THOUSANDS OF CUBIC FEET PER SECOND } T «A o 16 1 1 1 -20 0 20 & o 40 60 80 120 DISTANCE FROM BASELINE, IN FEET EXPLANATION 1965-Minimum elevation estimated from aerial photograph -o as -4 a----y _- May 22, 1985 o----a _ August 2, 1985 K----- x - October 9, 1985 6 s -s. December-7, 1985 + - January 13, 1986 July 7, 1975 (Howard, 1975) September 13, 1983 (Beus and others, 1985) August 1, 1984, (Beus and others, 1985) FIGURE 27. -Topography along profile 2 (see figure 11 for location) at Eighteen Mile Wash. 36 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA 50 100 A 45 |- - 98 s 40 |- - 96 Elevation of exposed deposit after recession 35 |- as |. - a---Cujanusry 15, 1986 § a 8f 1 CC f - < i | < Profile 1 I u>J 84 L 1 L 1 1 L L | 1 1 I T 1 ® Fa 100 T T T T T T T T T T T T T 3 6 o o 98 | | C o Jr | i 96 |- L - - a4 |- EXPLANATION A g2 | _ ®@----* August 4, 1985 § -__ p---O October 11, 1985 1 90 |- 1 - _ o---o December 7, 1985 A 88 | a---A January 15, 1986 | $9 : Profile 2 : 84 m 1 1 1 1 | 1 1 1 1 s Shoe | 0 10 ' 20 . 30° so 50° 60 . 10 . so 90 - 100 110%. 120. 130° A40 DISTANCE FROM INITIAL POINT, IN FEET 0 100 200 300 400 FEET <2 f____J__I____L'_—l 0 100 METERS Bedrock Edge of water FIGURE 34. -Surficial geology and topography along two profiles at Twenty-Nine Mile Rapid. Mapped on October 21, 1986; discharge, 5,600 ft*/s. 45 46 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA The upper surface of most surveyed reattachment deposits degraded during fluctuating flow. These changes were documented by bathymetric surveys at Eminence Break Camp, Blacktail Rapid, and National Rapid (table 8) and topographic surveys at Opposite Nineteen Mile Canyon, Saddle Canyon, and Hundred Twenty-Two Mile Creek (table 14). Only the deposit at the site Above Cathedral Wash aggraded. At this site, increase in volume occurred by vertical aggradation of about 0.5 ft as well as by upstream slipface migration of 10-20 ft. Parts of the reattachment-deposit crest ag- graded at Eminence Break Camp. At the site Above Cathedral Wash, constriction-ratio and reach-segment characteristics are similar to other sites, and variations in these parameters do not explain the apparently unique behavior of the site. Proximity to the Paria River, which contributes a large amount of sediment, may be important. Twenjy percent of the aggradation at the site was caused by sediment delivered by the Paria River on October 10 and 11. Between river miles 0 and 5, sediment finer than boulders covered 75 percent of the bed, a large amount for the Colorado River in the park, and aggradation may have resulted from greater local availability of sand-size bed material. As described in the section entitled "Bathymetric Surveys," aggradation occurred on the slope extending from the crest of the reattachment deposit to the thalweg at Blacktail Rapid. Decreased sediment transport was predicted by Randle and Pemberton (1987) throughout the river corridor, and aggradation along this slope probably occurred at other sites. COMPARISON OF CHANGES IN ALLUVIAL SAND DEPOSITS Aggradation and degradation occurred throughout the river corridor between 1983 and 1986. At some camp- sites, vertical aggradation of several feet occurred. Analysis of change in sand storage in all recirculation zones, however, shows that the number of reattachment deposits decreased 10 to 25 percent in the narrow reaches of Supai Gorge, Redwall Gorge, and Upper Granite Gorge (table 9). In Supai Gorge, major reattachment deposits also significantly decreased in area (table 10). In Muay Gorge, separation deposits inventoried as camp- sites decreased in area. In contrast, the number of deposits possibly increased in the wide reaches of Lower Marble Canyon and Furnace Flats (table 9). Area changes in these same reaches were not determined. Separation deposits were more stable than other types of deposits. Analysis of volume changes at Eighteen Mile Wash shows that vertical aggradation can occur without change in area exposed at low flow. Erosion of separation deposits in Muay Gorge probably is related to low- elevation debris fans in this reach (table 10). Reattach- ment deposits are more susceptible to change during high flow, as indicated by the percentage of deposits that have changed in number (table 9) or area (table 11). The response of channel-margin deposits is uncertain. Only in Muay Gorge was a significant change in total area measured. More than 50 percent of deposits increased in area. Classification of study sites evaluated by Beus and others (1985) suggests that small channel-margin depos- its in narrow reaches were eroded, although vertical aggradation occurred at other sites. These results indicate less change in major deposits due to high discharge in 1983-84 than that reported by Brian and Thomas (1984). Brian and Thomas (1984) inventoried campsites after recession of high flows in 1983 and recognized many new or enlarged alluvial sand deposits. They also reported that about 10 percent of the preexisting campsites had been significantly eroded. Their inventory, however, was made at a discharge of about 25,000 ft*/s. The difference in results suggests that changes in high-elevation parts of alluvial deposits were more significant than changes in low-elevation parts. Changes in area of high- and low-elevation parts of alluvial sand deposits were determined to evaluate top- ographic changes above and below an approximate stage corresponding to a discharge of 25,000 ft*/s (table 14). At . most sites, the area of the high-elevation part of the deposit above this stage increased or did not change between 1973 and 1984, whereas the low-elevation part typically decreased in size or did not change. These results show that although high-elevation parts of depos- its aggraded, low-elevation parts either degraded or did not change. Patterns of change determined for high- elevation parts are not necessarily consistent with changes in low-elevation parts. The onset of strongly fluctuating flows in October 1985 caused widespread erosion, especially in narrow reaches. Erosion of separation deposits occurred at sites as far as 167 mi downstream from Lees Ferry (fig. 33). Erosion was typically of the sand that had been deposited in 1983-85. Comparison of table 14 with figure 33 indicates that sites that eroded significantly between October 1985 and January 1986 also had eroded significantly from 1965 to 1973 and then had aggraded significantly during the 1983 high flows. For example, at Eighteen Mile Wash, Twenty-Nine Mile Rapid, and Fern Glen Rapid, signifi- cant erosion was measured between October 1985 and January 1986. These sites had eroded significantly be- tween 1965 and 1973 and aggraded in 1983. Significant aggradation was not followed by significant degradation in narrow reaches where a high separation deposit was armored from further erosion by exposed debris-fan deposits, as at Nautiloid Canyon. The high flows of 1983 and 1984, therefore, redistrib- uted much sand and removed sand from 10 to 25 percent SUMMARY 47 of recirculation zones in at least those narrow reaches within 160 mi of Lees Ferry. Significant aggradation, however, occurred at many major campsites. Aggrada- tion may have occurred in recirculation zones in wide reaches. Many new alluvial sand deposits eroded rapidly when exposed to strongly fluctuating discharges, which suggests that most of the gain in sand resulting from high flows was of short duration. SUMMARY This report has presented a classification of alluvial sand deposits, described some characteristics of these deposits, and described changes that have occurred in these deposits since completion of Glen Canyon Dam. The classification of alluvial sand deposits and the designation of reaches within the Grand Canyon were used to distinguish styles of change in narrow and wide reaches. Measurement of topographic changes in alluvial deposits were based on topographic and bathymetric surveys and analysis of aerial photographs. The largest and most numerous alluvial sand deposits along the Colorado River in Grand Canyon National Park are formed in zones of recirculating current. Recireula- tion zones are caused by large debris fans that partially block the channel and by minor bedrock or talus abut- ments. Alluvial sand deposits can be classified by form and location. Separation deposits are located near the point of flow separation, mantle debris fans, and extend to the edge of the primary-eddy return-current channel. Reattachment deposits are located near the point of flow reattachment and project upstream beneath the primary eddy. Channel-margin deposits are terracelike in form and may fill re-entrants or extend continuously along the channel in wide reaches for lengths of 1 mi. Channel- margin deposits probably are formed in recirculation zones. The Colorado River corridor in Grand Canyon National Park was divided into 11 reaches. Separation deposits large enough to be used as campsites are common throughout the river corridor in narrow and wide reaches. Reattachment and channel-margin deposits large enough to be used as campsites are common only in wide reaches except in the Muay Gorge, where channel- margin deposits are common. The form and sedimentology of alluvial sand deposits reflect the hydraulic and sediment-transport conditions existing during reworking and deposition of the deposit. Separation deposits form in lower velocity parts of the river than reattachment deposits and may be composed of slightly finer sand. At sufficiently high discharge, both separation and reattachment deposits are reworked, and sand is redistributed within the recirculation zone and between the recirculation zone and the main channel. This response to high flow is documented by repeated topographic surveys and sedimentologic analysis of study sites Above Cathedral Wash, at Eighteen Mile Wash, and Opposite Nineteen Mile Canyon and by repeated bathymetric mapping at Eminence Break Camp, Black- tail Rapid, and National Rapid. During recession from high flows, redistribution of sand within recirculation zones may result in degradation of the deposit. The high flows of 1983 and 1984 removed sand from recirculation zones in narrow reaches within 118 mi of Lees Ferry. When the rate of recession is great enough, topographic conditions at some sites cause flow to be directed away from a sand deposit and leave it exposed, such as at Eighteen Mile Wash. At other sites, especially reattachment deposits, redistribution of sand may continue even during a rapid recession. At many reattachment deposits, the result is erosion of down- stream areas and loss of sand to the main channel and redistribution of sand in other parts of the deposit within the recirculation zone. Higher rates of recession allow less time for this distribution and therefore may result in exposure of larger areas of alluvial sand deposits after recession at some sites. Fluctuating flows following high steady flows during the study period resulted in significant erosion. Fluctu- ating flows typically redistributed sand within recireula- tion zones and may deposit sand along the slope from the reattachment-deposit crest to the thalweg. Although erosion was significant throughout the park with the onset of fluctuating flow, results of topographic surveys by other investigators in the late 1970's indicate that equilibrium was reached after a few years. Topographic surveys between October 1985 and January 1986 indicate that such stability was not reached within 3-1/2 months of strongly fluctuating flow. Redistribution of sand can affect significant parts of alluvial sand deposits. Bathymetric surveying at three sites shows that net volume changes can occur in recirculation zones at a broad range of discharges. At each site, net volume changes indicate that large volumes of sand may be exchanged between recirculation zones and the main channel even at moderate or fluctuating discharges. The high flows of 1983 and 1984 eroded sand from recirculation zones in narrow reaches. The high flows may have resulted in aggradation of all types of alluvial sand deposits in wide reaches. Limited evidence suggests that high flows in 1985 caused further erosion of reat- tachment deposits in narrow reaches. Alluvial sand deposits used as campsites, whatever their type, are more stable than the smaller, lower- elevation deposits of the same type not used as camp- sites. Many campsites aggraded significantly during high flows in 1983. Fluctuating flows in 1985 and 1986 caused 48 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA rapid erosion of many deposits of all types throughout the Grand Canyon. The greatest erosion typically occurred at sites where significant deposition had occurred in 1983. The increase in sand at campsites from high flow there- fore is of limited duration if strongly fluctuating flows follow. During these same high flows, sand was removed from other recirculation zones in narrow reaches. Sepa- ration deposits are more stable than reattachment de- posits, although erosion can occur in reaches where separation deposits are of low elevation such as Muay Gorge. An inventory of campsites in 1983 showed that narrow reaches generally have few campsites. The high flows of 1983-85 followed by strongly fluctuating flows in 1985 resulted in accentuating the difference between campsite availability in narrow and wide reaches. REFERENCES CITED Anderson, TW., and White, N.D., 1979, Statistical summaries of Arizona streamflow data: U.S. Geological Survey Water-Resour- ces Investigations 79-5, 416 p. Beus, S.S., Carothers, S.W., and Avery, C.C., 1985, Topographic changes in fluvial terrace deposits used as campsite beaches along the Colorado River in Grand Canyon: Journal of the Arizona- Nevada Academy of Science, v. 20, p. 111-120. Birdseye, C. H., 1923, Plan and profile of Colorado River from Lees Ferry, Arizona to Black Canyon, Arizona-Nevada: U.S. Geological Survey topographic maps, 21 sheets, scale 1:31,680. Brian, N.J., and Thomas, J.R., 1984, 1983 Colorado River beach campsite inventory, Grand Canyon National Park, Arizona: Divi- sion of Resources Management, Grand Canyon National Park report, 56 p. Burkham, D.E., 1986, Trends in selected hydraulic variables for the Colorado River at Lees Ferry and near Grand Canyon, Arizona, 1922-84: U.S. Bureau of Reclamation, Glen Canyon Environmen- tal Studies Report, 51 p. Dolan, Robert, Howard, Alan, and Gallenson, Arthur, 1974, Man's impact on the Colorado River in the Grand Canyon: American Scientist, v. 62, p. 393-401. Dolan, Robert, Howard, Alan, and Trimble, David, 1978, Structural control of the rapids and pools of the Colorado River in the Grand Canyon: Science, v. 202, p. 629-631. Ferrari, Ronald, 1987, Sandy beach area survey along the Colorado River in the Grand Canyon National Park: U.S. Bureau of Reclamation, Glen Canyon Environmental Studies Report, 23 p. Folk, RL., 1968, Petrology of sedimentary rocks: Austin, Texas, Hemphill, 170 p. Graf, J.B., 1986, Sediment transport under regulated flow, Colorado River, Grand Canyon National Park, Arizona: Eos, American Geophysical Union Transactions, v. 67, no. 44, p. 950. Grand Canyon Natural History Association, 1976, Geologic map of the Grand Canyon National Park, Arizona: Grand Canyon, Arizona, Grand Canyon Natural History Association, scale 1:62,500. Helley, E.J., and Smith, W., 1971, Development and calibration of a pressure-difference bedload sampler: U.S. Geological Survey open-file report, 18 p. Howard, A.D., 1975, Establishment of benchmark study sites along the Colorado River in Grand Canyon National Park for monitoring of beach erosion caused by natural forces and human impact: University of Virginia Grand Canyon Study, Technical Report no. 182 p. Howard, A.D., and Dolan, Robert, 1979, Changes in the fluvial deposits of the Colorado River in the Grand Canyon caused by Glen Canyon Dam, in Lin, R.M., ed., First Conference on Scientific Research in the National Parks, v. 2, New Orleans, Louisiana, November 9-12, 1976, Proceedings: National Park Service Transactions and Proceedings Series, no. 5, p. 845-851. 1981, Geomorphology of the Colorado River in the Grand Canyon: Journal of Geology, v. 89, no. 3, p. 269-298. Hunter, R.E., 1977, Terminology of cross-stratified sedimentary layers and climbing-ripple structures: Journal of Sedimentary Petrology, v. 47, no. 2, p. 697-706. Kieffer,S. W., 1985, The 1983 hydraulic jump in Crystal Rapid-Impli- cations for river-running and geomorphic evolution in the Grand Canyon: Journal of Geology, v. 93, no. 4, p. 385-406. Laursen, E.M., Ince, Simon, and Pollack, Jack, 1976, On sediment transport through Grand Canyon: Third Federal Interagency Sedimentation Conference Proceedings, p. 4-76 to 4-87. Laursen, E.M., and Silverston, E., 1976, Camera stations along the Colorado River through the Grand Canyon-Supplement to the final report on the hydrology and sedimentology of the Colorado River: Division of Resource Management, Grand Canyon National Park, 150 p. [Unpublished report to the National Park Service.] Leopold, L. B., 1969, The rapids and the pools-Grand Canyon, in The Colorado River region and John Wesley Powell: U.S. Geological Survey Professional Paper 669, p. 131-145. Lojko, F.B., 1985, Beach sand grain size on the Colorado River in the Grand Canyon, in House, D.A., ed., Colorado River investiga- tions III: Flagstaff, Northern Arizona University, p. 85-98. Matthes, G.H., 1947, Macroturbulence in natural streamflow: Trans- actions of the American Geophysical Union, v. 28, no. 2, p. 255-262. Orvis, C.J., and Randle, T.J., 1986, Sediment transport and river simulation model: Fourth Federal Interagency Sedimentation Conference, v. 2, Las Vegas, Nevada, March 24-27, 1986, Proceedings, p. 6-65 to 6-74. Pemberton, E.L., and Randle, T.J., 1986, Colorado River sediment transport in Grand Canyon: Fourth Federal Interagency Sedimen- tation Conference, v. 2, Las Vegas, Nevada, March 24-27, 1986, Proceedings, p. 4-120 to 4-130. Randle, T.J., and Pemberton, E.L., 1987, Results and analysis of STARS modeling efforts of the Colorado River in Grand Canyon: U.S. Bureau of Reclamation, Glen Canyon Environmental Studies Report, 41 p. : Schmidt, J.C., 1986, Controls on flow separation and sedimentation in a bedrock river, Colorado River, Grand Canyon, Arizona: Geolog- ical Society of America Abstracts with Programs, v. 18, p. 741. Turner, R.M., and Karpiscak, M. M., 1980, Recent vegetation changes along the Colorado River between Glen Canyon Dam and Lake Mead, Arizona: U.S. Geological Survey Professional Paper 1132, 125 p. Webb, R.H., Pringle, P.T., and Rink, G.R., 1987, Debris flows in tributaries of the Colorado River, Grand Canyon National Park, Arizona: U.S. Geological Survey Open-File Report 87-118, 64 p. Wilson, R.P., 1986, Sonar patterns of Colorado riverbed, Grand Canyon: Fourth Federal Interagency Sedimentation Conference, v. 2, Las Vegas, Nevada, March 24-27, 1986, Proceedings, p. 5-133 to 5-142. TABLES 1-14; APPENDIX A TABLES 1-14 TABLE 1. -Summary of study sites and types of data collected 51 [X, indicates data were collected; dashes indicate no data collected; (DSS), detailed study site; N.A., not available. Time of study is that of bathymetric survey. number in parentheses] Discharges were estimated during bathymetric surveys or taken from nearest gaging station during day of work. Multiple bathymetric surveys indicated by Date and Discharge, Surface- Water- River Site time of in cubic feet Bathymetric Topographic Photographic flow surface Scour Sedimentology mile _ number study per second survey survey replications pattern slope chains (DSS) Above Cathedral Wash (original surveys) 2.5 1 05-18-85 44,1700 --- =-- X X _-» +-- ses 07-29-85 26,000-29,000 =-- --- X X --- a ik 08-29-85 (1530) 27,100 X --- X s A ser X 10-04-85 4,000-19,000 --- X X X --- X ass 12-07-85 2,600 --- X E e ve vei 01-09-86 (1600) 16,300 X X X X X X X 05-13-86 48,500 =-- =-- --- X ««- s re (DSS) Badger Creek Rapid (original surveys) 19 2 04-13-85 (1400) 17,900 X --- e #s« ece (DSS) Twenty-Nine Mile Rapid (original survey) ogo |. to. os gans 44,000 x x 08-04-85 23,000-29,000 =-- X X X ««» -.- X 10-11-85 4,000-15,000 =-- X X X --> ae hes 12-07-85 ~5,000 =-- X =-- --- --- --- --- 01-15-86 3,000-22,000 =-- X X X X a »« 52 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA TABLE 1. -Summary of study sites and types of data collected-Continued Date and Discharge, f Surface- Water- River Site time of in cubic feet Bathymetric Topographic Photographic flow surface Scour Sedimentology mile _ number study per second survey survey replications pattern slope chains (DSS) Nautiloid Canyon (initial survey, Howard, 1975) 34.7 10 _ 05-24-85 44,000-48,000 =-- X X X X --- «+ 08-04-85 23,000-29,000 =-- X X X --- + er 09-01-85 (0945) 27,600 x -.- =«> nee ses ves wes 10-12-85 3,000-15,000 =-- X X X --- s 01-14 to 01-15-86 2,360; 15,900 X(2) X X X X =-- ave Tatahatso Wash (initial survey, Ferrari, 1987) 37.3 11 _ 08-04-85 23,000-29,000 --- X X --- nee e ser 10-12-85 3,000-15,000 --- X --- *- #40 ee sew (DSS) Eminence Break Camp (original survey) 44.2 12 - 04-16-85 (0630) 26,100 X -.- --- o-- Per tse ses 04-17-85 (0645) 26,000 X --- --- X s --+ «e+ 05-25-85 40,000-47,000 --- X X X X _.- 08-05-85 25,000-31,000 --- X X X X «-. ¥++ 09-02-85 (0910) 27,200 X s E x+ k++ $+ Hs 10-12-85 3,000-15,000 --- X X X X «.- +. 01-16-86 (0915) 23,600 X X X X X --- X (DSS) Saddle Canyon (initial survey, Ferrari, 1987) 47.2 13 - 01-18-86 13,000-24,000 =-- ).€ =-- X X -.- --» 05-14-86 48,500 =-- =-- =-- X --- +-- srs EKwagunt Rapid (initial survey, Ferrari, 1987) 56.3 14 - 08-06-86 26,000-30,000 --- X X X =-- --- es 10-13-86 3,000-12,000 --- X --> a oes see yl Little Colorado River confluence (original survey) 61.1 15 04-19-85 (1240) 24,000 X --- --> e aes ise A 05-27-85 40,000-47,000 --- --- X X X =-- --- 08-06-85 26,000-30,000 --- X X X --- _. ess 09-03-85 (1105) 29,200 x «.> a se. e. += v 09-04-85 (0840) 26,500 X s s --» e ke« Css 01-17-86 (1535) 19,600 X s --- «-- «+> ses ere 01-18-86 13,000-26,000 =-- X X X --- =-- a++> Below Little Colorado River confluence (initial survey, Howard, 1975) 61.7 16 - 01-20-86 12,000-21,000 =-- X --- --- ««- «-~ nes Above Unkar Rapid (initial survey, Ferrari, 1987) 72.5 17 - 01-19-86 (1400) N.A. X --- +«> s ««- -- ++ 01-20-86 12,000-21,000 =-- X o a s -+» ess Nevills Rapid (original survey) 75.6 18 - 08-07-85 17,000-24,000 --- X X X --- --- --- 01-20-86 12,000-21,000 =-- X X X X --- =-- (DSS) Above Grapevine Rapid (initial survey, Howard, 1975) 81.1 19 - 05-29-85 44,000-46,000 --- X X X --- «» 08-07-85 17,000-24,000 =-- X X X E *-- oss 10-15-85 N.A. --- X X X --- --- d 01-21-86 12,000-18,000 --- X X X --- --- wes Cremation Camp (initial survey, Howard, 1975) 87.1 - % - 04-21-85 23,800-26,300 x(2) 05-30-85 45,000-47,000 =-- --- --- --- X --- --- 09-05-85 (1355) 29,300 X --- --- e ses ses a¥s 01-20-86 (1440) 17,800 X --- --- «=~ s es t> 01-21-86 (1150) 15,300 X s _- --» t === TABLES 1-14 TABLE 1. -Summary of study sites and types of data collected-Continued 53 Date and Discharge, Surface- Water- River Site time of in cubic feet Bathymetric Topographic Photographic flow surface Scour Sedimentology mile - number study per second survey survey replications pattern slope chains (DSS) Ninety-One Mile Creek (original survey) 91.0 21 - 08-08-85 19,000-24,000 --- X X ox =- se +4 10-15-85 N.A. --- X X +e oss ves 01-22-86 13,000-22,000 =-- X X X X +-- ¥ Trinity Creek 91.4 22 - 08-08-85 19,000-24,000 --- s X --- #9 01-22-86 13,000-22,000 --- =-- X «> ass #s ris (DSS) Granite Rapid (initial survey, Howard, 1975; Ferrari, 1987) 93.1, 23 - 05-31 to 06-01-85 42,000-47,000 --- X =-- X X s eee 93.4 08-09-85 18,000-22,000 --- X --- X e see e 01-22-86 13,000-22,000 --- X --- X --- se fre Ninety-Six Mile Camp 96.0 ° _ % 06-01-85 42,000-47,000 X 08-09-85 18,000-22,000 --- --- X es aik Khin Me 10-16-85 N.A --- --- X --= sex ses (DSS) Boucher Rapid (original survey) 96.6 25 - 08-09-85 18,000-22,000 =-- X X X X s see 10-16-85 N.A. --- X X X X a tse 01-23-86 15,000-22,000 === X X X =-- =~ +> Upper Crystal Rapid 98.0 26 - 01-22-86 (1610) N.A. X --- s -.- «s ¥es ¥e% Elves Chasm (original survey) 116.0 27 10-17-85 N.A. --- X X X n --- a¥s 01-24-86 15,000-23,000 --- X X X X --- ¥e+ (DSS) One Hundred Twenty Mile Camp (initial survey Ferrari, 1987) 119.7 28 - 08-11-85 19,000-23,000 =-- =-- X --- --- --- X 10-17-85 N.A. --- X X «-¥ se+ ass ask 12-08-85 6,000 s X --- l -es see ess 01-08-86 N.A. --- X --- +- ==> ses Pro (DSS) Lower Blacktail Rapid (original survey) 120.1 29 06-02 to 06-03-85 45,000-47,000 --- X X 4 X --- sex 08-12-85 16,000-22,000 =-- --- X X X _.» #s 09-07-85 (0805) 22,600 X --- --- ++ wes =s ssb 10-18-85 N.A. --- X X X X X --- 12-08-85 6,000 --- X --- --- --+ =s- wes 01-13-86 N.A. =-- X --- ««« X sys 01-24-86 (1435) 20,100 X --- --- -.- X sew One Hundred Twenty-Two Mile Rapid 121.6 30 - 06-05-85 44,000-46,000 --- =-- X X --> --+ hes 08-13-85 19,000-23,000 --- =-- X X --- ses eek 10-18-85 N.A. =-- =-- X X --- «-~ e> 01-26-86 21,000-25,000 --- --- X a «s a=s ess (DSS) One Hundred Twenty-Two Mile Creek (original survey) 122.0 31 06-05-85 44,000-46,000 =-- =-- X X =-- ««- X 08-13-85 19,000-23,000 --- X X X X =-- --- 10-20-85 7,000-13,000 --- X X X X --- X 12-08-85 6,000 --- X --- --- --- a --> 01-13-86 N.A. --- X =s» ses ses ze ss 01-25-86 18,000-26,000 --- X X X X --- X 54 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA TABLE 1. -Summary of study sites and types of data collected-Continued Date and Discharge, Surface- Water- River Site time of in cubic feet Bathymetric Topographic Photographic flow surface Scour Sedimentology mile - number study per second survey survey replications pattern slope chains The Cutbank 122.3 32 - 06-06-85 40,000-42,000 --- =-- X --- --- --- X 08-14-85 19,000-23,000 --- s X ses Ne' ¥«s Forster Rapid 122.6 33 - 06-06-85 40,000-42,000 --- s vss «-~ X Sse ex 08-14-85 19,000-23,000 --- s X -.- ==. ¥«< tre Enfilade Point (initial survey, Ferrari, 1987) 123.5 3M - 06-06-85 40,000-42,000 =-- --- X X --- == sis 08-14-85 19,000-23,000 =-- --- X X s eos ses 10-20-85 7,000-13,000 =-- --- X X --- «ts 01-27-86 23,000-26,000 =-- X X X --- s wey Stone Creek 131.8 35 - 06-08-85 30,000-35,000 --- --- X oes wes Sen 08-15-85 20,000-24,000 --- --- X -.- +-- Z- e- 10-20-85 N.A. --- s s ses or ass Opposite Deer Creek Falls 136.2 36 - 08-15-85 20,000-24,000 --- =-- X «= ««« ass ¥+ (DSS) National Rapid (original survey) 166.5 37 - 04-25-85 16,800-20,800 X(3) --- --- X X --- a+ 06-09 to 06-11-85 30,000 =-- X X X X --- X 08-15-85 20,000-24,000 --- X X X --- +-- oer 09-09-85 (1010) 22,200 X -.- e+ ase ere es hes 09-10-85 (1000) 21,200 X +-- wes ses ¥¥+ trs 10-21 to 10-22-85 8,000-17,000 --- X X X X --- ts 12-08-85 6,000 s X s ozs see fee ors 01-08-86 N.A. --- X ver sue vet I- sex 01-27-86 (1255) 21,100 X =.. see ook ask sed <¥s 01-28-86 (1615) 23,100 X(2) X X X --- <- ai+ (DSS) Fern Glen Rapid (Ferrari, 1987) 168.0 38 01-08-86 N.A. --- X s --- s <-> 01-30-86 16,000-23,000 --- X --- X X --- X One Hundred Eighty-Six Mile 185.8 30 - 04-27-85 (1410) 22,300 X --- s ««» =s ree Rev 06-12-85 30,000 =-- --- =-- X X --- #++ 09-11-85 (1040) 26,000 X --- s +-- oes «*% #++ 09-12-85 (0825) 26,000 X s ««» wes e a= i++ 01-29-86 (1545) 19,400 X -.- e sor <«. aes iss (DSS) Pumpkin Springs (original survey) 212.9 40 _ 04-29-85 (0835) 26,200 X s e+ ce» ««» whe tess 06-13-85 30,000-35,000 =-- X X X X --- X 08-16-85 20,000-22,000 --- X X X X --- X 09-13-85 (0915) 25,200 X --- A wes ses rex Fes 10-23-85 7,000-16,000 --- X X X --- s t+ 01-30-86 (1545) 25,900 X --- ««- e. «<+ tew sig 01-31-86 (0915) 21,400 X X X X X --- X Diamond Creek 225.2 41 _ 09-14-85 (1100) 25,000 X --- _- a c++ «-+ es 02-02-86 (1005) 23,700 X =-- e. ass e Pre sek TABLES 1-14 TABLE 2. -Characteristics of the reaches within the study area 55 Average Type of ratio of Average alluvial Reach Description top width channel Number of sand deposit (river Local name Major geologic of reach to mean width, Channel campsites typically used miles) of reach units at river level* width depth2 in feet* slope3 per mile as campsites 0-11.3 Permian Kaibab Limestone Wide 11.7 280 0.00099 0.4 Separation section Toroweap Formation Coconino Sandstone Hermit Shale 11.0-22.5 Supai Gorge Supai Group Narrow 74 210 0014 .9 Separation 22.6-35.9 Redwall Gorge Redwall Limestone Narrow 9.0 220 0015 .9 Separation 40.0-61.5 Lower Marble Muay Limestone Wide 19.1 350 0010 2.6 Separation; Canyon Bright Angel Shale reattachment Tapeats Sandstone 61.6-77 4 Furnace Flats Tapeats Sandstone Wide 26.6 390 0021 2.5 Channel margin Unkar Group 77.5-117.8 _ Upper Granite Zoroaster Plutonic Narrow 7 190 0023 .6 Separation; Gorge Complex channel margin Trinity and Elves Chasm Gneisses Vishnu Schist 117.9-125.5 Aisles Tapeats Sandstone Narrow 11 230 0017 3.9 Reattachment; Vishnu Schist channel margin; separation 125.6-139.9 Middle Granite - Tapeats Sandstone Narrow 8.2 210 0020 2.3 Channel margin Gorge Unkar Group Vishnu Schist 140-159.9 Muay Gorge Muay Limestone Narrow 1.9 180 0012 1.1 Channel margin 160-2138 Lower Canyon Basalt Wide 16.1 310 0013 BA = Muay Limestone Bright Angel Shale 213.9-225 Lower Granite Vishnu Schist Narrow 8.1 240 0016 9.9 ' .. ..... Gorge Modified from Grand Canyon Natural History Association, 1976. PAt 24,000 halo, average based on cross-section data from Randle and Pemberton (1987); cross sections at about 1-mile intervals. Based on predicted water-surface elevations at 24,000 A*/s (Randle and Pemberton, 1987). 4Campsites inventoried by Brian and Thomas (1984). ( OCT (ra ge" 29° 69 ; °° | | 8000° ECIS sSuudg urydung Op OCT OSS t ss LP 99° 6 ©}. J | 8800° O'89T pidey ual» og gg OET O6T OTe OP oL 00'T 00L'6 ©900° 9900° 9991 pidey jeuonen i OST O6T OLC Ad 9g OL 000's €2500° L000® O CoI 42094) @[IN OML -£yuom;, poipunp 2u0 1g OPT SST OLC £9" 89° PL 000's CLO0® 8OLO® TOS pidey [te:yoe|q 1om01 & O9T OIS O6T 58° 6 SL ..i 1 | c @.. 9000° L'6IT dures olnt poipunp sup # C9T C I8 p9° 000 TZ LTOO® ©600° 996 pidey G 06 OLL O66 IP IL 001 | . [ ftm % O f- ©800° PS6 pidey =& OST oL yess sg) N 0 eesens ll "C0 evens 6000° O'T6 xealp a[ oug-{10uN 1 OGT OST OLt ga 89° TL _ g ' ._.. 6000° T'T8 pidey sumade1; amoqgy - OPT s C 98° 68° pg° 008 ZZ £000 L000® CLP uokue; a[ppeS fT OBT OEC ureuw 'qsodap Jo 'eoue ut 'uornspeiSa( Jo sogyins 'eaue Ut 'uouneperddy aryoid out adorg sogjins 19ddp aguey> 19N a0ddn ut aBueyo agueys 19N aSuey> aSesoaay 9861 Arenuep-gg61t q0qtuardag g86t [epep ou 'sayseq 'our ay) Jo y13u01 ay; Aq sour aryoud Suore adueyo reonoA jou Jo eare ay; Surptap Aq pornduoo sem adueyo eoraoA aBeroay ms aAtssaoons 407 sour argoud usomjaq gare ut aduaraptp oy} se arom uonepexdop puse uonepe1d3y] shaains muamuhyg usanm;aq sabunya fo Rimuwung-'g aT9¥I, 62 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA TABLE 9. -Number of separation and reattachment deposits in recirculation zones between river miles 0 and 118, 1978 and 1984 Deposit type1 Total number Width Bias Reach of recirculation of of Reattachment Separation segment zones surveyed reach analysis1 Se - r- 1973 1984 1973 1984 0-11.3 36 Wide Decrease 31 28 18.5 19.5 11.4-22.5 40 Narrow Decrease 27 20.5 26 26 22.6-35.9 60 Narrow No bias 37.5 34 38.5 29.5 40-61.5 115 Wide Increase 96.5 100.5 49.5 50 61.6-77 4 37 Wide Increase 28 32 23.5 25 77.5-117.8 111 Narrow Increase 78.5 68.5 28.5 21.5 Total 399 298.5 283.5 184.5 177.5 1Change in number of deposits from 1973 to 1984 caused by difference in stage. TABLE 10. -Areas of major alluvial sand deposits in selected reaches, 1973 and 1984 [Values are in thousands of square feet] Types of deposits Reach Total Separation Reattachment Channel margin segment 1973 1984 Change 1973 1984 Change 1973 1984 Change 1973 1984 Change 0-113 _ 460-610 370-450 () 2102710 - 210250 - (2) - 100-130 - &4-100 (3 mas s.. 114-225 - 540-670 460-560 @ - sso4s30 - ssouso - (2) - 110-200 - se-110 (4 } alt Ccs... 22.6-35.9 - 480-620 490-590 (®) ~ mo-se0 . stosme '@) - (3) : -.. sl...... 122-1255 - 300-380 320-400 (3) : m... ia a.. a Breer 59-72 & - cm2-mo moelso (3 125.6-139.9 _ 840-920 810-990 (2) goozz0 - ggosso - (2) - iso-1so - iso-so - (2) - 410440 stoaso (2) 140-150 __ 128-150 120-150 C - 13s 55-67 () _ o 2 --.. i 64-78 C lErosion. *No change. TABLES 1-14 63 TABLE 11. -Number of deposits that underwent change, 1978-84 Types of deposits Reach segment Separation Reattachment Channel margin Upper pool Gain - Loss No Gain _ Loss No Gain - Loss No Gain _ Loss No change change change change 0-113 i 0 3 2 2 1 0 0 0 0 0 0 11.4-22.5 4 3 6 0 6 1 0 0 0 0 2 1 22.5-35.9 ° 2 6 6 1 1 2 0 0 0 0 1 2 122-125.5 1 1 0 2 0 1 7 2 0 1 0 1 125.6-139.9 6 3 5 2 2 0 7 9 4 l 1 2 140-150 0 2 1 1 0 0 7 0 2 0 0 0 Total 14 15 21 8 1 5 21 11 6 1 4 6 Percent 28 30 42 33 46 21 55 2 16 36 55 TABLE 12. -Classification of deposits studied by Howard (1975) and Beus and others (1985) [Study site names are those of Beus and others (1985). River mile in basket? is riv]er mile used in appendix A of this report. L, left side of river; R, right side of river Types of deposits and river-mile position Separation Reattachment Channel margin Upper pool Eighteen Mile Wash Nineteen Mile Wash) Nineteen Mile Wash) Upper Granite Rapid (18.2) [18.11] (19.3) [19.01] (19.3) [19.01] (93.2)(93.1L] Nautiloid Canyon One Hundred Ninety Mile Lower Nankoweap Blacktail Canyon (34.7) [34.71] (190.2) (53) [53.2R] (120.1) [120.0R] Below Little Colorado Grapevine River confluence (81.1) [81.11 (61.8) [61.7R] One Hundred Nine Mile Tanner Mine (109.4) (65.5) [65.61] Walthenberg Canyon Unkar Indian Village (112.2) (72.2) [72.5R) Upper 124.5 Mile Canyon Bedrock Rapids (124.3) (131) [131.0R] The Ledges (151.6) [151.6R] National Canyon (165.5) [166.4L] Lower Lava (180.9) Granite Park (208.8) Nineteen Mile Wash had one profile line across reattachment deposit and one profile line across channel-margin deposit. 64 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA TABLE 13. -Summary of measured changes at 20 sites during fluctuating flow, October 1985 to mid-January 1986 Length of Average River Deposit Date Profile - section, - vertical Description mile type in feet change2 Above Cathedral Wash 25 Reattachment 10-04-85 1 57 +0.6 Profile 1 across crest; profile 2 to 2 45 0.1 downstream of reattachment point 01-09-86 Badger Creek Rapid 19 Separation 10-05-85 1 5A +0.1 Figure 5 to 2 8&5 0.17 01-1186 3 9% +2.0 Soap Creek Rapid 114 Separation 09-21-85 1 87 -O.1 Separation point migrates to 2 83 -0.3 downstream through 01-1286 3 53 0.6 all cross sections 4 35 -0.7 5 3 -0.7 6 37 0.3 Below Salt Water Wash 122 Separation 10-08-85 1 16 +04 Low-velocity area to 2 57 02 01-13-86 3 45 +0.1 Eighteen Mile Wash 18.1 Separation 10-09-85 1 2 0.0 Figure 12 to 2 9 22 01-13-86 3 10 2.12 Opposite Nineteen Mile Canyon 19.0 Reattachment 10-10-85 1 57 -0.3 Profile 1 across bar crest; profile to 2 30 -0.3 2 downstream from reattachment 01-14-86 point Twenty Mile Camp 198 Separation 10-1185 1 17 05 About 120 feet downstream from to separation point 01-14-86 Twenty-Nine Mile Rapid 29.2 Separation 10-11-85 1 43 0.1 Figure 34 to 2 42 28 01-15-86 3 47 35 Nautiloid Canyon 34.7 Separation 10-1285 1 9 0.6 Profiles located progressively to 2 17 +0.2 farther downstream 01-14-86 3 20 +0.6 4 20 12 Eminence Break Camp 44.2 Separation 10-1285 1 18 -O.1 Figure 14 to 2 TO +0.0 01-16-86 3 2 -1.0 4 26 +1.7 TABLES 1-14 65 TABLE 13.-Summary of measured changes at 20 sites during fluctuating flow, October 1985 to mid-January 1986- Continued Length of Average River Deposit Date Profile - section _ vertical Description mile type in feet change2 Saddle Canyons 472 Reattachment 09-24-85 1 60 02 Figure 17 to 2 ® 0.1 01-1886 3 68 02 4 20 12 5 25 12 6 16 14 Above Grapevine Rapids 811 Channel 10-15-85 1 21 -10 Profile 1 between separation and to 2 2. -L1 reattachment points; profile 2 near 01-2186 reattachment point Ninety-One Mile Creek® 91.0 Separation 10-1585 i 15 -13 Profile 1 near separation point; to 2 3 -11 profile 2 primary-eddy current 01-22-86 National Rapid 1665 Separation 10-21-85 1 66 04 Figure 30 to 2 2 +0.3 01-08-86 3 - 0.0 Fern Glen Rapid 168.0 Separation 10-01-85 1 3 +0.7 Profiles located progressively to 2 15 +2.8 farther downstream 01-08-86 3 T2 +1.7 USBR 4 - 0.0 5 10 02 Pumpkin Springs 2129 Channel margin; 10-23-85 1 18 172 Profile 1 near reattachment point; reattachment to 2 25 -18 profile 2 downstream from 01-3186 reattachment point 1Length of section is that portion of cross section over which survey comparisons could be made and which were both affected by fluctuating flows; actual cross sections are longer. 2Average vertical change equals cross-section area divided by horizontal length of cross section. 3Surveys in January 1986 after conclusion of special fluctuating-flow study period; some change may be due to resumption of higher flows beginning January 17, 1986. 66 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA TABLE 14. -Areas of exposed sand at detailed study sites, 1965, 1973, and 1984 [Area is in thousands of square feet] Area of exposed sand Change1 Site* _ Deposit? Site name High Low High Low elevation* elevation? elevation elevation 1965 1973 1984 1973 1984 1965-73 1973-84 1973-85 2.5L R Above Cathedral Wash 35 18 17 64 59 - NC NC 7.9L S Badger Creek Rapid 43 35 29 42 55 - - + R Badger Creek Rapid 7.9 0 0 17 0 - NC - 114R S Soap Creek Rapid 85 86 9 110 99 NC NC NC 12.2L S Below Salt Water Wash 17 10 17 31 35 - + - 18.1L S Eighteen Mile Wash 11 4.0 6.9 15 15 - + NC 19.0L R Opposite Nineteen Mile Canyon 29 16 14 57 25 - NC - 19.8L S Twenty Mile Camp 21 20 21 33 30 NC NC NC 29.2L S Twenty-Nine Mile Rapid 23 19 25 51 53 - + NC 34.TL S Nautiloid Canyon 34 30 18 41 33 - + - R Nautiloid Canyon 0 0 0 32 66 NC NC + 44.2L S Eminence Break Camp 62 81 76 100 92 + NC NC R Eminence Break Camp 17 13 3.5 63 43 - - » 934L S Granite Rapid 5 0 6.1 NA NA - + NA 96.6L S Boucher Rapid 22 23 27 NA NA NC + NA 168.0R S Fern Glen Rapid 97 54 T0 % 100 - + NC R Fern Glen Rapid 5.0 0 0 19 12 - NC - 1NC, no change; minus sign, loss of area; plus sign, gain in area; NA, not applicable. River mile. L, left side of river; R, right side of river. 3B, reattachment; S, separation. AArea exposed at discharge of about 25,000 cubic feet per second. SArea exposed at discharge of about 6,000 cubic feet per second. APPENDIX A Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek River mile Aerial River mile inventory Side Site photo- _inventory ___ Deposit of graph types 19231 river number * 1973 _ 1983 / «se== Lees Ferry = 1.9 Left Unnamed site 1-141 1.9 2.0 Point bar 2.5 Left Above Cathedral Wash ! Sasce~ ~- eseaes Reattachment 2.7 Right Cathedral Wash 1-145 2.7 3.0 - Separation 5.7 Right Six Mile Wash 1-173 §;§g : -.««« Separation 7.9 Right Badger Creek Rapid 1-193 7.0 8.0 - Separation 7.9 Left Badger Creek Rapid 1-193 7.9 8.0 - Separation 10.3 Left Below Ten Mile Rock 1-211 sytem 10.2 - Reattachment 11.4 Right Soap Creek Rapid 1-219 s«e««= 11.5 - Separation 12.0 Left Salt Water Wash 1~223 = tees 30.4 _ Reattachment 31.9 Right South Canyon 2-102 31.5 31.5 Separation 33.5 Left Little Redwall Camp 2-114 33.5 33.7 Separation 33.7 Left Unnamed site 2-116 33.9 33.8 - Separation 34.7 Left Nautiloid Canyon 2-123 34.7 34.8 - Separation 35.1 Left Unnamed site 2-132 85.1 Separation 36.0 Left Thirty-Six Mile Rapid 2-138 36:0 - Separation 37.2 Right Unnamed site 2-147 37.2 ----- Reattachment ; 37.3 Left Tatahatso Wash 2-148 37 .% Upper pool 37.6 Left Below Tatahatso Wash 2-150 37.6 37.5 Upper pool 38.0 Left Unnamed site 2«154 'A= 38.4 - Separation; reattachment See footnotes at end of table. 67 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph hype3 19231 river number ~ 1973 - 1983 : 38.5 Left Unnamed site 2-157 38.6 38.8 - Channel margin; reattachment 39.9 Left Unnamed site 2-166 390.8 . +-- Separation 40.2 Left Unnamed site 2-168 40.1 - ~---- Channel margin; 40.9 Right Upper Buckfarm Canyon 2-173 40.9 40.9 _ Reattachment; upper pool 41.0 Right Lower Buckfarm Canyon 2-173 41.0 41.0 _ Separation 41.3 Right Bert Loper Canyon 2-205 41.93 - <--> Separation 41.5 Right Royal Arches 2-206 41,5 ----- Reattachment 42.0 Left Unnamed site 2~177 41,9. _ Channel margin 42.2 Left Unnamed site 2-178 42.1 42.3 - Channel margin 42.8 Left Unnamed site 2~101 :* 42.9 - Channel margin 43.1 Left Unnamed site 2-183 43.2 ----- Separation; 43.5 Left President Harding Rapid 2-184 43.4 43.3 - Separation 44 . 2 Left Eminence Break Camp 2-187 44,24. Separation 44.6 Left Unnamed site 2-191 44.5 44.6 Separation 44.8 Left Unnamed site 2-192 44.7 44.8 _ Reattachment; upper pool 44.9 Left Unnamed site 2-193 49.0 --=== Separation 45.3 Right Above Triple Alcoves .. _<<-<«« 45.3 Channel margin; Camp reattachment 45.9 Left Unnamed site 2-198 45.8 46.0 _ Upper pool 46.7 Right Triple Alcoves 2-203 46.8 46.5 - Reattachment; upper pool 46.8 Right Unnamed site 2-204 Marsh Marsh - Reattachment 47.0 Right Lower Triple Alcoves 2211 -. 46.6 - Separation Camp 47.2 Right Saddle Canyon 2-213 47.1 47.2 - Separation 47.3 Right Below Saddle Canyon -- <---- 47.3 - Reattachment 47.5 Left Unnamed site 2~215 - ~----- 47.5 - Separation 47.5 Right Unnamed site 2-215 =---= 47.8 - Separation; reattachment 47.7 Left Unnamed site 2-216 47.8 _ Reattachment 48.0 Left Unnamed site > 0 48.0 _ Reattachment 48.3 Right Unnamed site 2-219 48.3 ----- Reattachment ; upper pool 49.5 Left Unnamed site 2-225 ee«== 49.7 Reattachment ; upper pool 49.8 Left Unnamed site 2-226 49.5 49.9 _ Reattachment; separation 49.8 Right Fifty Mile Camp 2-227 ;.. ~-<=-~ 49.9 Upper pool 49.9 Right Dinosaur Camp 2-227 50.0 50.0 - Separation 50.3 Left Unnamed site 2-239 - _ <---- 50.2° Channel margin; reattachment 50.7 Left Unnamed site 2-232 50.6 50.6 - Reattachmet 31.1 Right Unnamed site 2-235 . 51.0 - Separation 51.2 Left Unnamed site 2-236 Marsh 51.5 - Reattachment 51.3 Right Unnamed site 2-236 =. ~---- 51.4 Reattachment 31.5 Left Unnamed site 2-237 Marsh ---~~~ Reattachment 51.9 Right Little Nankoweap Creek - 3-1 51.9 51.8 - Reattachment; upper pool 92.1 Right Unnamed site 3-2 52.0 = ----- Separation 52.3 Right Above Nankoweap Rapid 9~3 ... <. #««=« 52.3 Channel margin 52.5 Right Nankoweap Rapid 374 52.5 52.5 Channel margin 53.0 Right Nankoweap Rapid 3*7 ... ._. 52.7 Channel margin; See footnotes at end of table. reattachment APPENDIX A 69 Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph typos 1923+ river number ~ 1973 - 1983 53.2 Right Below Nankoweap Rapid 3-9 53.0 53.0 - Channel margin; reattachment 53.2 Left Unnamed site 3-9, 10 53.1 53.0 Point bar 53.4 Right Below Nankoweap Rapid 3-10 aesus 53.2 Separation 53.7 Left Unnamed site 3-12 53.3 53.4 - Channel margin; reattachment 53.7 Right Unnamed site 3-12 53.6 53.4 - Separation 53.8 Right Unnamed site 3-13 53,7. -««-- Channel margin; reattachment 53.8 Left Unnamed site 3-13 53.8 53.8 Channel margin 54.1 Left Unnamed site 3-14 | | _ 54.0 - Separation 54.2 Right Unnamed site 3-15 \ | ~«««<« 54.0 - Separation 54.3 Right Unnamed site 3-16 54.2 54.2 - Reattachment; upper pool 54.4 Right Unnamed site 3-17 54.5 ----- Reattachment 54.5 Left Unnamed site 3-17 Marsh 54.4 - Upper pool 54.6 Left Unnamed site 3818 __ "««««« 54.6 - Channel margin 54.7 Left Unnamed site . _ _ --««- 54.7 - Reattachment 55.0 Left Unnamed site 3~2Ll . [; «=== 55.0 Upper pool;. reattachment 59.1 Left Unnamed site 3821 ._ 55.2 Separation 55.3 Left Unnamed site 3-22 Marsh 55.4 - Reattachment 55.6 Right Unnamed site 3-24 Marsh ----- - Reattachment 56.3 Right Kwagunt Rapid - _". «sees 56.2 - Reattachment 56.4 Right Below Kwagunt Rapid __ ----- __ --~--~- 56.4 - Channel margin 56.5 Right Unnamed site 3-28 56.6 56.5 Channel margin; reattachment 56.8 Left Unnamed site 3-29 56.8 56.8 Channel margin 57.0 Left Unnamed site 3-30 see~= 57.0 - Separation 57.5 Right Malagosa Canyon 3-33 57.4 57.5 - Separation 57.6 Left Unnamed site 3-34 57.7 57.5 - Reattachment 58.2 Right Awatubi Canyon 3-37 #«#*== 58.2 Separation 58.6 Left Unnamed site 3-39 58.5 58.7 Separation 58.9 Right Unnamed site 3740 *x«=s 58.5 Upper pool 59.0 Left Unnamed site 3-41 59.0 59.0 - Reattachment; 59.5 Right Unnamed site ©. _. ~=4«-= 59.5 Channel margin 59.8 Right Sixty Mile Rapid 3+4§ ___ «=««« 59.8 - Separation 60.2 Left Unnamed site 3-48 - -. ----- 60.0 _ Reattachment; upper pool 60.6 Right Unnamed site 3*S91 . : 60.5 Separation 61.1 Right Unnamed site 3-53 _ _ «<--- 61.2 - Reattachment; upper pool 61.4 Left Island Camp ...> .. ==«-- 61.8 Separation; reattachment 61.7 Right Below Little Colorado 3-50. . . <== 61.9 - Separation River confluence 62.3 Right Unnamed site 3-61 62.4 62.3 Upper pool 63.3 Right Unnamed site 3-68 53.3 . ---«-- Separation 64.0 Left Unnamed site 3-71 53.9 . Reattachament 64.7 Right Carbon Creek 3~75 64.5 64.5 - Separation 65.4 Right Lava Canyon Rapid 3-79 65.5 65.5 - Reattachment; upper pool 65.6 Left Palisades Creek 3-82 65.5 65.6 Separation 66.0 Left Unnamed site 3-84 66.1 . -~---- Channel margin 66.4 Left Unnamed site 3-86 66.4 66.5 Reattachment; See footnotes at end of table. channel margin 70 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph types 1923+ river number * 1973 - 1983 66.8 Left Espejo Creek 3-90 66.9 66.8 Channel margin; separation 67.3 Left Comanche Creek 3-92 67.3. .+«««- Channel margin 67.7 Left Unnamed site 3-94 67.7] + -s««« Channel margin 67.8 Right Unnamed site 3-94 -««== 67.8 - Channel margin 68.0 Right Upper Tanner 3-96 68.0 68.0 Point bar 68.2 Right Unnamed site 3-97 68.1 68.2 Point bar 68.6 Left Tanner 3-101 68.7 68.6 Channel margin 68.7 Left Tanner 3-101 68.8: ----- Point bar 69.3 Left Below Tanner 3-111 69.5 69.0 Point bar 69.4 Right Upper Basalt Rapid 3-112 69.5 69.6 - Channel margin 69.8 Right Lower Basalt Rapid 3-113 see«= 69.8 Channel margin 69.9 Left Unnamed site 3-114 69.9 ----- Channel margin 70.2 Left Unnamed site 3-116 70,2 - ~~-«= Channel margin 70.3 Right Unnamed site St117 |. ««««« 70.3 - Channel margin 70.5 Right Unnamed site 3~117 _, «««« 70.5 - Channel margin 70.9 Left Unnamed site 3-120 Marsh - ----- Channel margin; reattachment 71.3 Left Cardenas Creek 3~1241 | = _ 71.3 - Separation 71.4 Left Unnamed site 3-121 Marsh . ----- Reattachment 74.7 Left Unnamed site .._ 71.7 - Channel margin 71.9 Right Unnamed site 3~126 _ -«««-« ----- _ Separation 72.1 Left Unnamed site 3-128 72.1 72.1 Point bar 72.86 Right Above Unkar Rapid 3-120 | - ----- 72.5 - Channel margin 72.6 Right Middle Unkar Rapid 3~180 ._" " <«-«« 72.6 - Channel margin 72.7 Left Unnamed site 3-192 - = ----- 72.7 - Channel margin 73.1 Right Lower Unkar Rapid 3-133 infrtnbated 73.1 - Channel margin 73.4 Left Unnamed site 3-135 73.4 73.3 - Channel margin 73.7 Left Unnamed site 3-137 79.7] - <<--- Channel margin 73.7 Right Granary Camp 3-137 73.7 - Channel margin 73.9 Right Unnamed site 3-138 73.9 ----- Channel margin 74.0 Right Unnamed site 3-138 74.0 _ ----- _ Separation 74.2 Left Unnamed site 3-140 74.2 ----- Channel margin 74.3 Left Unnamed site 3-142 74.3 74.4 - Channel margin 74.3 Right Unnamed site 3-142 74.9 | ----- Separation 74.7 Left Unnamed site 3-144 74.7 74.7 - Channel margin 74.7 Right Unnamed site 3144 ___ 74.6 - Channel margin 74.9 Left Escalante Creek 3-145 74.9 74.8 - Upper pool 75.0 Right Unnamed site . _ =~<«-«« 75.0 - Channel margin 75.6 Left Nevills Rapid 3-148 75.5 75.5 - Separation 75.8 Right Opposite Papago Creek 3~192 <_ '~ 75.8 - Reattachment 76.5 Right Unnamed site 3-156 76.4% - ~<<«- Channel margin 76.6 Left Above Hance Rapid 3-156 76.5 76.4 _ Reattachment; upper pool 77.2 Left Unnamed site 3-161 77.1 ----- Channel margin 78.8 Left Sockdolager Rapid 3-168 Upper pool 81.1 Left Above Grapevine Rapid 3-181 81.1 81.3 Channel margin; reattachment 82.6 Right Eighty-Two and One- 3-189 82.6 ----- Channel margin Half Mile 84.0 Right Clear Creek 3-197 84.0 ----- Separation; reattachment 84.4 Left Above Zoroaster Rapid 3-201 84.4 ----- _ Separation 85.7 Left Cremation Creek 3-207 85.7 ----- Channel margin 87.1 Left Cremation Camp 3-215 87.1 87.1 Separation 87.2 Right Roys Beach Camp 3-216 | -:--«- 87.1 Channel margin 88.0 Left Unnamed site 3-220 88.0 - ~---~- Channel margin See footnotes at end of table. APPENDIX A T1 Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph type 1923+ river number ~ 1973 - 1983 89.3 Right Below Pipe Springs Rapid 3-228 89.3 89.5 Channel margin 90.9 Left Unnamed site 3-239 91.1 90.8 - Separation 91.0 Right Ninety-One Mile Creek 2-240 91.2 91.2 Separation 91.4 Right Trinity Creek 3-242 $1.5: -«<«--- Separation 92.2 Left Unnamed site 3-246 92.2 92.1 Channel margin 93.1 Left Upper Granite Rapid 4-7 93.2 93.4 - Reattachment; upper pool 93.4 Left Granite Rapid 4-7 93.3 93.6 - Separation 94.2 Left Unnamed site 4-12 szews Separation 94.2 Right Ninety-Four Mile Creek - 4-12 93.9 94.3 - Separation 94.9 Left Hermit Rapid 4°1§5 : ;- 94.7 _ Upper pool 95.8 Left Old Dune Camp 4-22 95.8}. ~~-<-- Channel margin; reattachment 96.0 Left Ninety-Six Mile Camp 4-23 95.9 95.6 Channel margin 96.6 Left Boucher Rapid 4-27 96.5 96.7 Separation 98.0 Right Upper Crystal Rapid 4-36 98.1 Upper pool 98.2 Right Crystal Rapid §*37 ; . . <===== 98.3 Separation 99.0 Left Tuna Creek Above Rapid - 4-41 99.1 - <~<--- Channel margin; reattachment 99.1 Right Tuna Creek Rapid 4-42 99.1 : =-«-- Upper pool 99.5 Left Unnamed site 4-43 99.5. ----- Point Bar 102.7 Right Below Turquoise Rapid 4-67 102.9 ----- Channel margin 103.1 Right Shady Grove; One 4-68 103.1 ----- Channel margin Hundred-Three Mile One Hundred-Four -73 103.8 103.8 Upper pool; Mile Rapid reattachment 105.6 Right One Hundred-Five and 4-83 105,606: «<--- Upper pool; One-Half Mile reattachment 106.8 Right One Hundred-Seven 4-93 106.8 . ~~-«- Channel margin Mile 107.0 Right Above Bass Rapid 4-95 107.5 107.7 Channel margin 107.3 Left Bass Canyon 4-96 107.7; ««-«-« Channel margin 107.4 Right Bass Rapid 4-97 107.9 108.0 Channel margin 107.6 Right Unnamed site 4-99 108.2 - -~~-~-- Reattachment 107.8 Right Lower Bass Camp 4-101 108.3 108.2 Channel margin 108.1 Right Shinumo Rapid 4-100 |.. 108.6 - Channel margin 112.6 Right Unnamed site 4-132 112.8, «««=« Separation 114.0 Right Unnamed site 4-141 |_ ~~~«= 114.0 - Channel margin 114.4 Right Upper Garnet Canyon 4-144 114.3 114.5 - Separation 114.6 Right Lower Garnet Camp 4-145 114.9; ««--- Channel margin 115.6 Left Royal Arch Trail Camp 4-153 115.4 115.4 - Channel margin 115.7 Right Unnamed site §=154 -\. 115.5 - Separation 115.8 Right Monument Fold Camp 4-155 115.7 115.6 - Reattachment; separation 117.0 Left Below Elves Chasm 4-161 117.0 116.8 - Separation 117.3 Left Unnamed site 4-163 117.4 117.2 Channel margin 117.7 Left Stephen Aisle 4-165 117.7} ....=««-- Channel margin 118.0 Right Unnamed site 4"167: : 118.1 Upper pool 118.3 Right Unnamed site 4-169 - ---~-- 118.6 - Reattachment 118.5 Left Apache Terrace 4-170 118.5 188.6 Channel margin 118.7 Right Unnamed site 4-171 118.7 118.8 - Reattachment 118.9 Left Unnamed site 4-172 119.8. =«--- Channel margin 119.1 Right One Hundred Nineteen 4-173 119.2 119.0 - Reattachment Mile Camp 119.2 Left Unnamed site 47174 119.2 119.1 Separation See footnotes at end of table. 72 AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph typos 19231 river n 1973 - 1983 119.4 Right Unnamed site §~175¢ <= / ~s--- 119.3 - Channel margin 119.4 Left Unnamed site 419 <- 119.4 - Reattachment 119.7 Left One Hundred Twenty 4-176 119.7 119.8 Channel margin; Mile Camp reattachment 119.8 Right Unnamed site 4~177 % _ _ ~«<«-- 119.8 - Reattachment 120.0 Left Unnamed site 4-178 119.98 ----- Channel margin 120.0 Right Upper Blacktail Rapid 4-178 120.1 120.0 Upper pool 120.1 Right Lower Blacktail Rapid _ *=-««<- 120.2 Separation 120.2 Left Opposite Blacktail Rapid 4-179 120.5 120.5 Channel margin 120.5 Left Below Blacktail Rapid 4-181 120.5 120.5 Separation 121.5 Left Unnamed site 4-186 121.6 - ~--~-< Upper pool 121.6 Left One Hundred-Twenty- 4-187 121.7 121.8 - Separation Two Mile Rapid 121.8 Left Unnamed site 4-188 121.0 - ~-~-- Channel margin 122.0 Right One Hundred Twenty- 4-189 122.0 122.2 - Reattachment; Two Mile Creek upper pool 122.2 Left Unnamed site 4-190 122.2 - ----- Channel margin 122.3 Left The Cutbank §*181 >_ ~-««« 122.2 - Reattachment 122.6 Left Forster Rapid 4-192 122.7 122.6 - Reattachment; upper pool 122.7 Left Unnamed site 4-193 122.8 -.~---- Channel margin 122.9 Left Unnamed site 123.0 - Reattachment 123.2 Left Upper Enfilade Point §=107 awe«es Channel margin Camp 123.5 Left Enfilade Point 4-198 123.5 123.2 Separation 123.8 Right Unnamed site 4200. < =: 124.0 - Channel margin 124.2 Left Unnamed site 4202 | «=-~--- 124.6 Channel margin 124.3 Left Unnamed site 4-202 124.4 - 124.8 - Separation 124.6 Left Fossil Rapid 4~205 - _ <«-«- 124.9 - Channel margin 125.2 Left Below Fossil Rapid 4-207 125.2 ----- Channel margin 125.2 Right Unnamed site 4207 ° ~ 125.2 Channel margin 125.4 Left One Hundred Twenty-Six 4-208 125.4 125.8 - Channel margin; Mile Camp reattachment 125.5 Left Unnamed site 4-209 125.5 125.8 - Channel margin reattachment 126.1 Left Unnamed site 4-213 126.2 126.0 Separation 126.3 Right Randy's Rock 4-215 126.3 126.5 Upper pool 127.7 Left Below bedrock 4-224 127.7" ---- Separation 131.0 Right Above Dubby 4-244 131.0 131.0 Separagion 131.1 Right Unnamed site 42406 ° " 131.3 Channel margin 131.4 Right Just above Dubby 4-247 131.6 131.8 Upper pool.; channel margin 131.8 Right Stone Creek 4-249 131.9 132.0 - Separation; reattachment 132.0 Left Unnamed site 574 192.1 . ----- Channel margin 133.0 Left Opposite One Hundred 53°11 133.1 133.0 - Separation Thirty-Three Mile Creek 133.1 Left Racetrack St11 "_" _ *===« 133.1 - Reattachment 133.4 Right Upper Tapeats ° '~ 133.7 - Channel margin 133.7 Right Tapeats Creek Mouth §~14. ~' 133.8 - Channel margin 133.8 Right Unnamed site 5-15 _ '* "~«««< 133.9 - Channel margin 133.8 Right Lower Tapeats Rapid 133.9 133.9 - Channel margin 134.1 Left Unnamed site 5~17 134.2 134.1 - Channel margin 134.5 Left Unnamed site 5-20 134.5 134.5 - Separation; reattachment See footnotes at end of table. APPENDIX A 73 Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph types 19231 river number * 1973 - 1983 134.8 Left Owl Eyes Camp 5-22 @-: ®ee=e« 134.8 - Channel margin 134.7 Right One Hundred Thirty, 5-31) #===~ 134.8 - Channel margin Five Mile Rapid 134.8 Right Above Granite Narrows §-31 .>... %===s 134.9 - Channel margin Camp 136.1 Left Granite Narrows Camp 5-29 196.0: +--- Channel margin 136.2 Left Opposite Deer Creek 5-31 136.2 136.2 Channel margin Falls 136.4 Left Lower Deer Creek Camp 5-32 136.4 136.5 Separation 136.5 Left Unnamed site 5-32 136.5 136.6 - Channel margin; reattachment 136.6 Left Unnamed site §$-33 - #*|~ ====- 136.7 Channel margin; reattachment 136.7 Left Above Poncho's Kitchen - 5-34 ___ -~-~~~~ 136.8 - Separation; Camp 137.0 Left Poncho's Kitchen Camp 5-36 197.0: ----- Separation 137.0 Left Lower Poncho's Camp 5-36 197.1 ' --«-- Reattachment; 137.1 Left Below Poncho's Camp 5-37 =:! =-s«-= Separation 137.4 Left Unnamed site 5~380 - _ ' 137.3 Channel margin 137.3 Right Unnamed site $-39 /+... ®ssmer ---=« Separation; reattachment 137.5 Right Unnamed site 9-30 :|. g*-== 137.3 - Channel margin 137.6 Left One Hundred Thirty- 5-40 137.7 137.5 Channel margin Seven and One-Half Mile Rapid 137.9 Left Unnamed site 5-42 137.9 137.8 - Separation 138.2 Left Unnamed site 5-44 138.3 138.0 - Separation 138.4 Left Unnamed site 5-45 139;.6. ----- Channel margin 138.6 Right Unnamed site 5-46 =~«== 138.7 - Reattachment 138.9 Right Fishtail Rapid 5-48 138.9 139.0 Upper pool 139.3 Left Unnamed site 5-51 139.4 139.5 Channel margin 139.3 Right Unnamed site §~351 199.4 i ~<=«- Channel margin 139.7 Left One Hundred Forty 5~53 139.7 139.8 - Reattachment; Mile Canyon upper pool 139.9 Left Unnamed site 5-54 139.9 % ---«-- Separation 140.2 Left Unnamed site 5-56... ._ «=== 140.3 - Channel margin 141.0 Left Unnamed site 5~60-. : :: --== 141.0 - Separation; Reattachment 141.4 Left Unnamed site 562 . i ==-«- 141.4 _ Channel margin 142.4 Right Unnamed site 5-60 | | .. <---- 142.5 - Channel margin 143.4 Left Above Kanab Rapid 5-74 143.3 143.4 - Channel margin 143.1 Right Unnamed site 5-174. -, z==~- 143.0 - Channel margin 143.5 Right Mouth of Kanab Creek 5-75 . <_ 143.5 - Channel margin 145.0 Left Unnamed site §~B84 --= 145.1 Channel margin 145.6 Left Olo Canyon 5-88 145.4 145.5 - Separation 147.7 Right Spring Above . _ '~-=== 147.7 Channel margin Matkatamiba Rapid 147.9 Right Matkatamiba Rapid §-103 . =----- 147.8 - Channel margin 148.5 Left Lower Matkatamiba Rapid 5-106 148.3 148.4 Channel margin 149.7 Right Upset Rapids 5-114 149.8 149.7 - Separation 151.6 Right Ledges Camp 5-122 151.6 151.8 Rock 152.3 Left Unnamed site 5-128 182.9 ----- Separation 153.6 Right Sinyala Rapid 5-133 153.5 Separation 153.8 Left Sinyala Ledges Camp 5-135 153.0 _----- Rock 154.9 Right Rockfall Lower Ledges 5-140 «_ *+«=~*< 155.0 - Channel margin reattachment 155.7 Right Last Chance Camp 5-146 155.6 155.7 Upper pool See footnotes at end of table. 7A AGGRADATION AND DEGRADATION OF SAND DEPOSITS, GRAND CANYON NATIONAL PARK, ARIZONA Comparison of river mile inventories of 1973 and 1983 from Lees Ferry to Stone Creek-Continued River mile Aerial River mile inventory Side Site photo- inventory Deposit of graph typos 1923+ river number ~ 1973 - 1983 155.8 Right Unnamed site S*146: =_: ;_===-= Separation 156.3 Right Unnamed site 5~150 - ~---- 156.2 Channel margin 156.6 Left Unnamed site S~151 ° >< <---- 156.5 Channel margin 157.8 Right Unnamed site 5~158 ._ 157.7 - Channel margin 158.0 Left Unnamed site - - 157.8 - Channel margin 158.3 Right Unnamed site 5-159 158.1 ----- Channel margin 158.7 Right Unnamed site 5-161 158.6 158.5 Channel margin 159.4 Right Unnamed site 5-167 ----- 159.3 Separation 159.9 Left Unnamed site 5-170 159.8. : ~--~- Channel margin 160.4 Left Unnamed site 5-172 «===> 160.4 - Channel margin 160.7 Right Unnamed site S115 160,7 : <«-~- Separation 161.6 Right Unnamed site $"180 -::. «===s 161.6 Channel margin 162.0 Left Unnamed site sS-182 - 4---- 162.0 - Separation 162.1 Left Unnamed site 5-182 . «««««= Channel margin 162.4 Left Unnamed site 5-184 ----- 162.5 Channel margin 162.8 Unnamed site 5-187 _ ----- 163.0 Upper pool; Reattachment 163.1 Right Unnamed site $=189 .- _... 163.2 Separation; Reat tachment 163.3 Left Unnamed site 5=190 . -. 163.5 Channel margin 163.9 Left Unnamed site 5-193 163.9 163.9 - Channel margin 164.5 Right One Hundred Sixty-Four 5-199 164.5 164.5 Separation Mile Rapid 164.9 Right Unnamed site 5~202., .., ----- 165.0 - Channel margin 165.0 Left Unnamed site 5-202 - .. ----- 165.0 - Reattachment 165.1 Right Unnamed site 5~208 - . ==--- 165.2 - Reattachment 165.7 Left Unnamed site 5~206 .-: j<--=~ 165.7 - Reattachment 165.8 Left Unnamed site §~207 _.. ==-- 165.8 Channel margin 165.9 Left Unnamed site 5-207 ===== 166.0 - Separation 165.9 Left Unnamed site 5-208 Channel margin 166.3 Left Above Upper National 5-210 ; Channel margin Rapid 166.4 Left Upper National Rapid 5-211 166.5 166.5 Channel margin Reattachment 166.5 Left National Rapid S-211 166.6 166.6 Separation River mile located to nearest 0.1 mile based on 1923 survey (Birdseye, 1923) as plotted on 1984 aerial photographs. umber of aerial photographs on which site is located (U.S. Bureau of Reclamation, 1984 series). argest deposit type listed first. # U.S. GOVERNMENT PRINTING OFFICE: 1990-785-046/3036 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA nergy: Report prepared jointly by the U.S. Geological Survey A and the National Oceanic and Atmospheric Administration UG 16 199 {Y CB GA; %4 '£.,’~n‘: 4 % U.5. DEposiTORY JUL 3 4 1991 U.S.|GEOLOGICAL SURVEY PROFESSIONAL PAPER 1494 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA By E.H. CHIN, National Oceanic and Atmospheric Administration, and B.N. ALDRIDGE and R.J. LONGFIELD, U.S. Geological Survey U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1494 Report prepared jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1991 UNITED STATES UNITED STATES DEPARTMENT OF THE INTERIOR DEPARTMENT OF COMMERCE MANUEL LUJAN, Jr., Secretary ROBERT A. MOSBACHER, Secretary UNITED STATES NATIONAL OCEANIC AND GEOLOGICAL SURVEY ATMOSPHERIC ADMINISTRATION Dallas L. Peck, Director John A. Knauss, Administrator Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging in Publication Data Chin, Edwin H. Floods of February 1980 in southern California and central Arizona. (U.S. Geological Survey professional paper ; 1494) "Prepared jointly by U.S. Geological Survey and National Oceanic and Atmospheric Administration." Bibliography: p. Supt. of Does. no.: I 19.16:1494 1. Floods-California, Southern. 2. Floods-Arizona. I. Aldridge, B.N. (Byron Neil) II. Longfield, R.J. III. Geological Survey (U.S.) IV. United States. National Oceanic and Atmospheric Administration. V. Series: Professional paper (Geological Survey (U.S.); no. 1494. GB1399.4.023C47 1991 551.48'097949 88-600327 For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 CONTENTS Page 0220200200200 e+e +++ revers veer evr eevee rere ever rere errr reer errr reek 1 . 22 00 eee eee eevee avea eee ee. 1 Purpose and Scope................. 2 Met@OrOIOGiCAl e+e +++ eee eevee ree ree ree 2 Antecedent Circulation PAtt@ePNS keke eee 0} 2 Development of Storms, February 13-21 ............ 5 Rainfall 62+ e+e e+e reer reer err ee. 10 Beginning Meteorological Conditions, February 13-14 ....... 12 Precipitati0n eee eee verre reer reek 19 California Floods ................... 26 Geographic Setting .......... 26 Floods Of J@NU@rY 1980 eee reer rere errr ee 28 Floods of February 13-21, 31 Volumes of Runoff and Effect on Reservoirs .............. 33 Floods in Major River Basing }}}. 34 S@ItOM SA 626 eee eee eee reer eee 34 Tijuana River BASIN keke eee reek 60k 34 Otay and Sweetwater Rivers ..........................}}. 34 San Diego River BASIN eee eee} 35 San Dieguito River 37 San Luis Rey River }}}} 37 Santa Margarita River Basin ............................. 39 Santa Ana River BASIN kee ekke ek 40 San Gabriel and Los Angeles River Basins .......... 45 Coastal Basins North and West of Los Angeles.... _ 47 Page California Floods-Continued Effect of Floods on Ground-Water Levels ........................ 49 COAStAl DAMAGE eee rere err err err err err err err reas 49 Monetary Damage and Flood Relief................................ 50 Sediment TTANSDOTE eee eer eer rere ere reer erea 52 aon ee 53 GeOGTAPRIG S@ttIMQG eee eee reer ere ere eee es 53 Minor Floods in Little Colorado, Bill Williams, and Upper Gila River BASIMS eee eee eee eek} 57 Major Floods in Lower Gila River Basin............... 57 Antecedent eee eee eek 0. 57 Salt River Upstream From Roosevelt Dam................ 58 Verde River Basin Upstream from Horseshoe Dam.... 60 Flooding Downstream from Reservoirs on the Salt and Verde RiVeN$ eee eer eer eer eer eee} 63 Agua Fria and Hassayampa Rivers........................... 66 FIOOQ eee eee ree re errr rr err errr erea reas 67 Postflood Reservoir e... 00}. 68 Recurrence Intervals of Peak Discharges............................... 70 Summary of Flood Stages and Discharges.............................. 71 +e eee eee eer ere errr reer aree reas 71 SUMM@TY eee eevee err erver ere nevere rev serre reer evere rere ek 72 Ref@T@MCES eee eee ere ree errr ere neer e aree 73 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Map showing sites in southern California where streamflow data were obtained for floods of February 1980. 2. Map showing sites in Arizona where streamflow data were obtained for floods of February 1980. 3. - Map showing damage information and time and date when floodwaters reached selected road crossings in and near Phoenix, Arizona, February 13-20, 1980. Page FIGURE 1, 2. Maps showing: 1. = REDO reese eer ese err rer err res eres res rere rere reer rer rere ere sr eer rere ee 2 2. Sectional hemispheric 500-millibar analyses: 0400 hours P.s.t., February 11-12, 1980 4 3. GOES infrared images of storms, 0145 or 0415 hours P.s.t., February 13-21, 1980, showing storms 1-6.......................... 6 4-6. Graphs showing: 4. Evolution of precipitable Water, FebTU@ryY 12-22, 1980 esr sess rrr rss rrr essere er errr errr errr rrr ees 11 5. - Evolution of K index, FeDTU@ryY 12-22, 1980 er err err err err revers errs errr reese errr esses reer errr eee ees 11 6. - Evolution of lifted index at three locations, and daily rainfall at San Diego, Calif., February 12-22, 1980 .............. 12 LI IV FIGURES 7-16. 17. 18-21. 28. 25. 26-30. 31. 32. 38. 34. 35, 36. 37, 38. 39. 40, 41. 42. 48-45. CONTENTS Page Maps showing: 7. Net vertical displacement of the 700-millibar pressure surface during the 12-hour period ending at 0400 hours P.s.t., February 14, 1980, and K indices and trajectories of air parcels at the ending time ........................ 13 8. Analyses of relative humidity and vertical velocity, 1600 hours P.s.t., February 13, 1980, and 0400 hours F@DIUAYY 14, 6666s 66 e+e ves eevee reer rre renee reer errr rre r eerie reer rre neer renee neenee nne 14 9. 300-millibar analyses, 1600 hours P.s.t., February 13, 1980, and 0400 hours P.s.t., February 14, 1980 .............. 15 10. 500-millibar analyses, 1600 hours P.s.t., February 13, 1980, and 0400 hours P.s.t., February 14, 1980 .............. 16 11. 850-millibar analyses, 1600 hours P.s.t., February 13, 1980, and 0400 hours P.s.t., February 14, 1980 .............. 17 12. Surface analyses, 1600 hours P.s.t., February 13, 1980, and 0400 hours P.s.t., February 14, 1980 .................... 18 13. Climatic divisions in CaliforNiA ANd eee eer eer eer eer rer err err err rer rer rere rr rer rere errr renee neer ener nee 19 14. Selected climatological stations in SOUthWEeSt@MN CalifOPNIQ eee eer vere revere rer rer rer rer rer rer rrr errr rre 21 15. Selected climatological stations in Arizona and SOUthe@Stern e+e +e vers rer rere errr rer reer ees 22 16. Radar summaries at 0635 hours P.s.t. and 1335 hours P.s.t., February 14, 1980 rere rer rere rer} 24 Graphs showing precipitation mass curves for selected stations in southern California and central Arizona, FebrU@YY 13-22, 1980 rere eee reer reece reer eerie neenee neenee neenee ree reer ner renner ner nene 25 Maps showing: 18. Isohyetal analysis of total storm precipitation greater than 5 inches in southern California from approximately 0600 hours P.s.t., February 13, through 2400 hours P.s.t., February 21, eee eer errr ere 26 19. Isohyetal analysis of total storm precipitation greater than 2.5 inches in central Arizona from approximately 0600 hours m.s.t., February 13, through 2400 hours m.s.t., February 21, keer eer rere ree} 27 20. Approximate areas of California affected by major flooding in January and February 1980 ........... 28 21. Natural provinces Of SOUtR@PN CAIfOPMI® eevee vere erver erver rer rere errr r err rrr errr renner rene nner rrr r neenee 29 Schematic map showing major reservoirs and streams in San Diego County, Calif., and in the Tijuana River basin Of MEXICO és ees Fives ren bessie sees bener ner nen anser nre sien er aba bach arsis ser here Pn e besser he ine sn s 30 Hydrograph of daily discharge for East Twin Creek near Arrowhead Springs, Calif. (station 11058500), JADU@ry-MAICh 1980 ses reer rer res ieri eerie reer renee reer err err rrr rrr rrr rr errr ne s 31 Aerial photographs showing flooding along the Tijuana River in California on January 30, 1980, near Interstate Highway 5 and Dairy Mart Road looking southwestward at outlet to Pacific Ocean and at Imperial Beach Naval Air Station looking southward downstream from levees about 3 miles from international boundary............... 32 Hydrograph of daily mean discharge for Tijuana River near Nestor, Calif. (station 11013500), January-March 1980 ....... 35 Aerial photographs showing: 26. Moreno Valley, Calif., looking northward up San Vicente Creek downstream from San Vicente Reservoir, FeDFU@YY 21, 1980 rre rre reese reer eer reer reer reer erie reer er ner neenee neenee nee nene 36 27. Lakeside, Calif., looking westward, FebTU@ry 21, 1980 e+e reve ever rer verre r rer rer rere rr rrr errr rr rrr e nes 37 28. San Diego River in lower Mission Valley, San Diego, Calif., looking westward, February 21, 1980................... 38 29. Racetrack and fairgrounds at Del Mar, Calif., looking eastward up the San Dieguito River, February 21, 1980 .. 39 30. Industrial-park complex near Oceanside, Calif., flooded by San Luis Rey River, looking northeastward from bluff behind San Luis Rey Mission, FebTU@ry 21, 1980 eer err err err err err err err rrr errr errr rere ree} 40 Hydrograph of daily discharge for Murrieta Creek at Temecula, Calif. (station 11043000), December 1979- FebrUATY 1980 , ;,; ... . . bry echos bes iri renee nie rind bondi atin dr n esr ern ers bood neenee nev br hee 41 Map showing major reservoirs and streams in Orange, San Bernardino, and Riverside Counties, and in the San Gabriel River basin in LoS Angeles COUNtY, 6s sees rer re rre reer eevee reer rer rer rer rer rer reer rrr err rer rrr rer ene 42 Aerial photograph of Prado Dam and Flood Control Reservoir, Calif., looking northward from Santa Ana Canyon, February 1980, just after maximum storage had been obtained in the P@S@PVOI eee eee ere rre rre rere err ener 43 Hydrograph showing contents of Prado Flood Control Reservoir, Calif., January-April eee eer err err eee} 44 Photographs of: 35. Flooded homes along Hampshire Avenue below Harrison Canyon debris basin in San Bernardino, Calif., February 1980, showing debris basin and extent of SEdiMeNt ee eee reer errr errr reer rrr errr ees 44 36. Flood damage in San Jacinto, Calif., FeDPU@TY 1980 eee eve v erver rre rer rrr rer rrr eer rer rrr errr errr rene renee nes 46 Hydrographs of: 37. Daily discharge for San Jacinto River near Elsinore, Calif. (station 11070500), January-April 1980................... 49 38. Contents and stage of Lake Elsinore, Calif., February, March, September 1980 eevee rere reer} 50 Aerial photographs of Lake Elsinore, Calif., looking eastward, cirea 1950 and February 1980 eee} }} 51 Photographs of: 40. Residential area along Lake Elsinore, Calif., FeDFU@YY e+e erver err err err err err errr rrr errr reer reer} 52 41. Santa Ana River at 5th Street bridge in Santa Ana, Calif., showing dry channel prior to February 1980, at dis- charge of about 5,000 cubic feet per second on March 3, 1980, and extent of damage in late spring 1980 ...... 54 Map showing Los Angeles River basin and other major coastal stream basins in Los Angeles and Ventura Counties, C&L: 0s corer vir ir ves serier reteset di een ees teres bers inh esses adi ted ess ess ber bse rev es res nes res hes ne 56 Photographs of: 43. San Gabriel River below Santa Fe Dam, Calif., looking upstream prior to the 1980 flood and during FebDrU@ry 1980 esse erver server verse rrr errr rrr rire errr renner renner renner errr neer renner renee nees 58 44. House along Topanga Canyon, Santa Monica Mountains, near Santa Monica, Calif., February 20, 1980 ............. 60 45. Flooding at Point Mugu, U.S. Naval Air Station, Pacific Missile Test Center, Calif., February 18, 1980............ 61 FIGURE CONTENTS 46. Hydrograph showing changes in ground-water level in well at Baldwin Park, Calif. (1§/10W-7R2), 1977-80 .................. 47. Photograph of damage to residential structures and severe erosion of beach from surf activity south of Oceanside Harbor breakwater at Oceanside, Calif., 1980 eves ers errr erver rer server rrr rere errr reer ee ree ree nee 48. Graph of suspended-sediment discharge versus combined water and sediment discharge at Santa Clara River at Montalvo, Calif. (station 11114000), selected periods, 1969, 1978, 1980 errs errr rere ese reer rer es 49-52. Hydrographs showing: TABLE 1. 13. 14. 15. 16. 17. 18. 20. 21. 24. 25. 49. Discharge of Black and Salt Rivers upstream from Roosevelt Dam, Ariz., February 14-22, 1980...................... 50. Discharge of Verde River upstream from Horseshoe Dam, Ariz., February 14-22, 1980 e}} 51. Discharge of Salt, Verde, and Gila Rivers, Ariz., downstream from reservoirs, February 13-22, 1980............... 52. Discharge of Agua Fria River, Ariz., FebFU@ry 14-22, 1980 rere rere verre errr reer reer ee rer rer reeks 53. Aerial photograph showing Agua Fria River at Interstate Highway 10 near Avondale, Ariz., FebDIU@YY 20, 1980 errr esses rer ress esr ers esses ers ree rr rere reer ener serre esr errr err rre rer reer rere ener rna nee TABLES Meridional-temperature gradient per 10 degrees of latitude, observed at 0400 hours P.s.t., February 15, 1980, compared with long-term climatological averages for February over the Pacific Ocean at various pressure levels .......................... Precipitation at selected stations in southern California and Arizona during January and February 1980 .............................. Average precipitation and departure from normal in California and Arizona during January and February 1980, by CliM@tit vere eee erver eevee verre rere rrr errr renee rer eer reer err rere rene rere sree ener neenee neenee neenee neenee neenee Comparison of precipitation amounts observed during the storms of February 1980 with estimated 100-year amounts at selected stations in southern CaliforMi@ ANd ATIZON® seers esses essere reece rere sree rere errr rer reer err reer er rere Peak discharges at selected gaging stations during major floods in SOUth@rN e+ eee eee eee eer eer Mean discharges for 7 and 15 consecutive days at selected sites in southern California during floods of 1980......................... Peak inflow and outflow from selected reservoirs in southern CalifOPNi@, 1980 sess rss reverses servers esses secs ees Sediment loads at selected stations in southern California during major storm periods, 1969, 1978, and 1980 water years ....... Annual sediment loads at selected stations in southern California for 1969-80 Water rere errr rre errr eee. Gage height and discharge, February 14-22, 1980, at gaging station 09498500, Salt River near Roosevelt, Ariz. ................... Gage height and discharge, February 14-22, 1980, at gaging station 09499000, Tonto Creek above Gun Creek, near AVIZ. see seer ee ree server veer veer reer eer ens ree res res reer esen ener eer err eres neenee rec errr ener neenee nees Gaged inflow to Roosevelt Lake and outflow from Stewart Mountain Dam, Ariz., for periods when the 7-day gaged inflow exceeded 200,000 ACre-f@@t, esses reer seee essere reer rere ere rere ere reer errr errr reer errr errr ree Gage height and discharge, February 13-22, 1980, at gaging station 09508500, Verde River below Tangle Creek, above HOrS@ShO@ D&M, AVIZ. seres se seers sree reese sree reese seres rere eer rere eres reer reer rere reer neer reer ee eee Gage height and discharge, February 13-25, 1980, at gaging station 09502000, Salt River below Stewart DAM, crse reese errs nere reer nees Gage height and discharge, February 13-25, 1980, at gaging station 09510000, Verde River below Bartlett Dam, Ariz. ......... Gage height and discharge, February 14-24, 1980, at gaging station 09512170, Salt River at Jointhead Dam, at PhOGNIX, ATI. res res tester teeters es Gage height and discharge, February 15-23, 1980, at gaging station 09519500, Gila River below Gillespie Dam, Ariz............. Gage height and discharge, February 13-21, 1980, at gaging station 09512500, Agua Fria River near Mayer, Ariz. ............... Gage height and discharge, February 14-22, 1980, at gaging station 09512800, Agua Fria River near Rock Springs, Ariz....... Inflow and outflow, February 14-22, 1980, Lake Pleasant, Agua Fria River at Waddell Dam, Ariz. Gage height and discharge, February 14-22, 1980, at gaging station 09513970, Agua Fria River at Avondale, Ariz. .............. Summary of flood damage in the Phoenix, Ariz., area, FeDTU@YY 1980 eves verse erver verse essere ever reese errr ree Summary of flood stages and discharges at selected gaging stations in southern California Summary of flood stages and discharges in the Gila River basin of Arizona ..................... Known aerial photographic coverage of southern California available from government agencies for the floods of January ANG +e reer seres reeves reer seres seee resis res ses reese reese reece err reer nere ener reer rene cee Page 62 62 63 65 66 67 69 Page 78 79 80 81 82 83 85 87 122 VI GLOSSARY METRIC CONVERSION FACTORS For readers who wish to convert measurements from the inch-pound system of units to the metric system of units, the conversion factors are listed below: Multiply inch-pound units By To obtain metric units inch (in) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) square mile (mi*) 2.590 square kilometer (km*) acre 0.4047 hectare (ha) cubic foot per second (ft*/s) 0.02832 cubic meter per second (m*/s) acre-foot (acre-ft) 0.001233 cubic hectometer (hm) ton, short 0.9072 megagram (Mg) degree Fahrenheit (°F) (temp °F-32)/1.8 degree Celsius (°C) GLOSSARY [A number of terms are defined below according to their use in this report. If a word can be used as either a noun or a verb, only the noun form is defined.] Acre-foot. -The quantity of water required to cover 1 acre to a depth of 1 foot. It equals 43,560 cubic feet, 325,851 gallons, or 1,233 cubic meters. Baroclinic instability. -A hydrodynamic instability arising from the existence of a meridional-temperature gradient. Capacity (of a reservoir). -The volume of water, in acre-feet, that a reservoir can contain to the top of a spillway or gates. Contents. -The volume of water, in acre-feet, in a reservoir or lake. Contents is computed on the basis of a level pool or reservoir backwater profile and does not include bank storage. Convection. -Vertical motions and mixing resulting when the atmo- sphere becomes thermodynamically unstable. Convective cloud. -A cloud that owes its vertical development, and possibly its origin, to convections. Coriolis parameter. -Twice the component of the Earth's angular velocity about the local vertical, 20 sin &, where Q is the angular speed of the Earth and ¢ is the latitude. Crest (of a flood). -The point at which a stream stops rising. Crest is distinguished from "peak," which refers to the highest crest during a flood. Cubic feet per second (ft*/s). -A rate of discharge. One cubic foot per second is equal to the discharge of a stream of rectangular cross section 1 foot wide and 1 foot deep, flowing at an average velocity of 1 foot per second. Cyclogenesis. -Any development or strengthening of cyclonic cireula- tion in the atmosphere. Cyclonic curvature. -Counterclockwise curvature (in the Northern Hemisphere). Del-operator. -The operator, written V, used to transform a scalar field into the ascendent vector of that field. Discharge. -The quantity of fluid mixture, including dissolved and suspended particles, or sediment alone, passing a point during a given period of time. The water mixture is measured in cubic feet per second; sediment is measured in tons per day. Drainage area. -The area, measured in a horizontal plane, that is enclosed by a topographic divide. Drainage area is measured in square miles. Echos. -In radar terminology, a general term for the appearance of a radar indicator of the electromagnetic energy return from a target. e-fold time. -Time required for the amplitude of a perturbation wave to grow to e (=2.718...) times its initial amplitude. Entrainment.-The mixing of environmental air into a preexisting cloud parcel. Equivalent potential temperature. -The temperature an air parcel would have after undergoing dry adiabatic expansion until all moisture is precipitated out, then dry adiabatic compression to a pressure of 1,000 millibars. Extratropical Low (extratropical cyclone). -Any cyclone-scale storm that is not a tropical cyclone. Usually refers only to the migratory frontal cyclones of middle and high latitudes. Flood. -Any abnormally high streamflow. Flood peak. -The highest value of the stage or discharge attained by a flood. Front. -The boundary separating two different airmasses. Gage height. -The water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term "stage," although gage height is more appro- priate when used with a reading on a gage. Gaging station. -A particular site on a stream, canal, lake, or reser- voir where systematic observations of gage height or discharge are made. Gas constant. -The constant factor in the equation of state for perfect gases. Geostrophic approximation.-The assumption that the horizontal wind may be represented by the geostrophic wind (whose direction and speed are determined by a balance of the pressure-gradient force and the force due to the Earth's rotation). GLOSSARY Hydrograph.-A graph showing gage height or stage, discharge, or other property of water with respect to time. Inflow. -The water flowing into a reservoir or lake. Designates volume, in acre-feet, or discharge, in cubic feet per second, or is used as a general descriptive term. Instability. -Areas of instability; in this report, areas where the lifted index is less than 4. Isobar. -A line of equal or constant barometric pressure. Isohyetal map. -A map showing lateral distribution of precipitation, drawn as contours of equal rainfall amounts. Isotherm. -A line of equal or constant temperature. Jetstream. -Relatively strong winds concentrated within a narrow stream in the atmosphere. K index. -A measure of thunderstorm potential based on the vertical temperature lapse rate, the moisture content of the lower atmo- sphere, and the vertical extent of the moist layer. K=(Tsso- T500) + Td,850_ (Tz00- 711,700), where T and T,, represent temperature and dew-point tempera- ture, respectively, and numerals denote pressure levels-for example, T; s;, is dew-point temperature at 850 millibars. Knot. -A rate of speed of 1 nautical mile per hour, equal to 1.105 miles per hour. Commonly used to express windspeed. Lifted index.-A stability index based on the difference, in degrees Celsius, between the 500-millibar environmental temperature and the temperature of a parcel of air lifted adiabatically from or near ground surface to the 500-millibar level. Millibars.-A pressure unit, equivalent to 1,000 dynes per square centimeter, convenient for reporting atmospheric pressure. Miscellaneous site. -A site where data pertaining only to a specific hydrologic event are obtained. National Geodetic Vertical Datum of 1929 (NGVD of 1929). -A geodetic datum derived from a general adjustment of the first- order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. Peak. -The highest crest during a flood. Peak discharge. -The highest instantaneous discharge during a flood. Measured in cubic feet per second. Also termed "maximum dis- charge." Peak of record. -The highest instantaneous discharge recorded dur- ing a period of gaging-station operation. Peak stage.-The maximum height of a water surface above an established datum plane; same as peak gage height. Precipitable water. -The total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified surfaces (in this report, between ground surface and the 500-millibar level). Pressure surface. -A surface of constant atmospheric pressure. Probability. -The likelihood that a specific discharge will be equaled or exceeded in any given year; expressed as a decimal value between 0 and 1.0. Radiosonde. -A balloon-borne instrument package for measuring and transmitting meteorological data. Rainfall mass curve.-A graph of the accumulated rainfall depth, plotted as an ordinate, against time or duration of storm, plotted as abscissa; the curve represents total precipitation depth throughout the storm. Rawinsonde. -A meteorological data-collection system including a radiosonde and reflectors for measuring winds by radar. VII Recurrence interval. -As applied to flood events, the average number of years over a long period of time during which a given flood peak will be equaled or exceeded once. For example, a 50-year flood discharge will be exceeded on the average of once in 50 years. If the probability of the flood occurring is 0.02, there is a 2-percent chance that such a flood will occur in any given year. Ridge. -An elongated area of relatively high atmospheric pressure. Runoff.-That part of the precipitation that appears in streams. Measured as a volume, in acre-feet, or as a rate, in cubic feet per second. Saturation.-The condition in which the partial pressure of water vapor is equal to its maximum possible partial pressure under existing environmental conditions. Scour. -An increase in depth or width of a stream caused by flowing water removing material (usually unconsolidated) from a stream- bed or streambank. Sea level. -See National Geodetic Vertical Datum of 1929 (NGVD of 1929). Sediment. -Solid particles usually derived from rocks or earth mate- rial that have been or are being transported laterally or vertically from one or more places of origin. Sounding.-A single complete radiosonde observation of the upper atmosphere. Spill. -The water that passes over the spillway of a dam whether or not the spillway is equipped with gates. Distinguished from the more general term "release," which may include water flowing through penstocks and other openings at lower elevations than the spillway. Stage-discharge relation. -The relation between gage height and the amount of water flowing in a stream channel. Temperature. -Expressed in degrees Fahrenheit (°F) or Celsius (°C). The relation between these temperature scales is given in the conversion table at the front of this report. Time of day.-Expressed in 24-hour time. For example, 6 p.m. is expressed as 1800 hours P.s.t. (Pacific standard time). Tropopause. -The boundary between the troposphere and the strato- sphere, usually characterized by an abrupt change of lapse rate. Troposphere.-That portion of the atmosphere from the Earth's surface to the tropopause-that is, the lowest 10 to 20 kilometers of the atmosphere. Trough. -An elongated area of relatively low atmospheric pressure. Unfilled capacity (of a reservoir). -The volume of storage that is available for controlling the amount of water released. It is the difference between the contents of a reservoir at any given time and the capacity of the reservoir. Vapor pressure. -The pressure exerted by the molecules of a given vapor; in meteorology, the term is used exclusively to denote the partial pressure of water vapor. Vorticity. -A vector measure of local rotation in a fluid flow defined as the curl of the velocity vector: Vx V. In meteorology, it usually refers to the vertical component: dv _ du dx _ dy Zonal component.-The wind component along the local parallel of latitude. Z-R equations. -Empirical equations relating the rainfall rate (R) as a function of a measure of the hydrometeor size spectrum (Z). FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA By E.H. Cnn of the NatroNALt WrEatHER SERvIcE, NaTIONAL OcEaAntc and ATMOSPHERIC ApmINISTRATION, and B.N. Aupriner and R.J. LonoriEup of the U.S. Grorocicar SurvEy ABSTRACT A series of six Pacific cyclones struck the Southwestern United States during February 13-21, 1980. Pacific subtropical westerlies drove upper level troughs across the Western United States, thus weakening the normal mean ridge, displacing the Great Basin High, and exposing southern California and Arizona to the storm track. The coastal plains and valleys of southern California received between 5 and 10 inches of rain, and large areas in the coastal mountains received more than 15 inches. The central mountains of Arizona received 3 to 16 inches, and severe flooding resulted. The floods of February 1980 caused extensive damage along coastal streams of southern California. All but one major reservoir in San Diego County spilled. The peak discharge of the Tijuana River exceeded any previously recorded discharge since 1936. Levee breaks near San Jacinto in Riverside County caused extensive property damage. Lake Elsinore in eastern Riverside County reached the highest level since 1917 and flooded many homes and businesses. Erosion and bridge damage was severe along the Santa Ana River. On many streams the volume of runoff for 7 to 15 consecutive days was the greatest ever recorded for that number of days. Strong winds and high waves damaged the coast of southern California. Many mudflows and slope failures occurred in and near Los Angeles. Damage from flooding, mudflows, and beach-front erosion totaled about $500 million in south- ern California. Seven southern California counties were declared eligible for Federal disaster aid. Eighteen people lost their lives in California. Severe flooding occurred near Phoenix, Ariz., when the volume of flow into reservoirs on the Salt, Verde, and Agua Fria Rivers exceeded the unfilled capacity. The floods were the highest since 1905 on the Salt River at Phoenix, since 1919 on the Agua Fria River downstream from Waddell Dam, and since at least 1916 on the Gila River below the Salt River. The flood caused $63.6 million in damage in Maricopa County and at least $16 million in damage in other Arizona counties. Three Arizona counties were declared eligible for Federal disaster aid. Three people died in the flood in Arizona. INTRODUCTION Beginning February 13, 1980, six storms moved in from the Pacific Ocean in rapid succession and battered southern California and central Arizona. The storms Manuscript approved for publication May 4, 1987. originated over warm ocean waters at low latitudes, carried abundant moisture, and were steered toward the Southwestern United States by the subtropical jet- stream. Precipitation in southern California during Feb- ruary was the highest or second highest over periods of as much as 108 years. In California, the February storms were preceded by two severe storms in January that had soaked soils, decreased unfilled reservoir capacities, and generally set the stage for the flooding caused by the February storms. Severe flooding resulted from the February storms along streams that drain to the Pacific Ocean south of San Francisco and along streams that drain the central mountains of Arizona. The flood area is shown in figure 1. Strong onshore winds and exceptionally high tides caused coastal flooding and erosion. Extensive flooding occurred in San Diego County. Inflow to reservoirs in Arizona exceeded available storage capacities, and large releases from water-conservation reservoirs caused flooding downstream from the reservoirs. Peaks of record occurred at about 40 gaging stations in California and 10 gaging stations in Arizona. The volume of runoff was among the highest recorded in the 20th century. Large releases from many reservoirs and high lake levels lasted for several months. Mudflows and slope failures in the Los Angeles met- ropolitan area destroyed or damaged hundreds of homes. Contamination from raw sewage carried to the ocean by two streams caused several miles of southern California beach to be closed to swimming or surfing for periods as long as 14 months. Many miles of beach were eroded by high surf. The floods caused 18 deaths and about $500 million damage in California. About $80 million in damage and three deaths occurred in Arizona. Seven counties in southern California-Santa Barbara, Ventura, Los Angeles, Orange, San Bernardino, Riverside, and San Diego-and three counties in Arizona-Gila, Yavapai, and Maricopa-were declared eligible for Federal disas- ter aid. 122° 38 ° FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 116 ° San Francisco CALIFORNIA 36 ° 34° 200 MILES | 1 | 1 ] o 32° | UTAH | NEV AD A | aa -im 1. i | \ | | - _ coconino | [ \ 1 i 6000 U ARIZONEA EAPACHE!‘ | ~ 1 Flagstaff | | ® ° I' NAVAJO '| L_ ._ .-> ~" GREENLEE Lula _ ke = " COCHISE --A FIGURE 1. -Report area (shaded). PURPOSE AND SCOPE This report is one in a continuing series of joint reports undertaken by the National Weather Service in the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce and the U.S. Geological Survey of the Department of the Interior to document flood events. Meteorology associated with the precipitation of February 13-21, 1980, the distribu- tion of the precipitation, flood conditions in a basin- by-basin format, and pertinent hydrographic data are presented. Brief discussions of storms and runoff in January show the antecedent effect of these storms. Meteorological and hydrological analyses related to the February floods in this report are intended to provide a framework for hydrologic planning, as well as to serve as a comprehensive reference. The report concentrates mainly on flooding in the coastal basins of California south of about latitude 35° N., the Salton Sea basin (pl. 1), the Salt, Agua Fria, and Hassayampa River basins of central Arizona, and the Gila River basin downstream from the Salt River (pl. 2). The report area includes all or parts of the 10 counties that were declared disaster areas (fig. 1). Limited amounts of data are provided for streams in Apache, Coconino, Mohave, and Yuma Counties of Arizona. Precipitation data are sum- marized for the entire area of the two States. The January floods affected areas outside the general report area. Flooding in those areas was not severe enough to justify a detailed analysis but is discussed in a general way. Stream networks and station locations are shown on plates 1 and 2 (in pocket). All times given in the report are local standard time (Pacific, P.s.t., in California and mountain, m.s.t., in Arizona) unless stated otherwise. METEOROLOGICAL SETTINGS ANTECEDENT CIRCULATION PATTERNS The mean tropospheric circulation over the Pacific Ocean in December 1979, as represented by the mean 700-mb (millibar) map, showed predominantly zonal flow with low-amptitude waves. This pattern was replaced in January 1980 by more amplified waves, together with a blocking ridge over the eastern tip of Siberia and southward-displaced westerlies. Over the central Pacific, a large area of cyclonic curvature was present. Strong westerlies with mean speeds 7 to 8 m/s (meters per second) larger than normal occurred just north of the Hawaiian Islands. The mean 700-mhb zonal windspeed METEOROLOGICAL SETTINGS 3 profile for the western half of the Northern Hemisphere for January showed a maximum at latitude 30° N. This represented a southward shift of 15° from the position of maximum westerlies in December 1979. As a result, storm tracks over the Pacific were displaced southward and a much higher than normal amount of rain fell over California and Arizona in January. The southward displacement of the westerlies and the amplification of waves in the mean 700-mb flow continued in February. Meanwhile, a very cold continental polar airmass from the interior of Siberia had been moving off the east coast of Asia. As the cold airmass spread out eastward and southward into the central Pacific, ex- tensive belts of enhanced baroclinicity were formed at relatively low latitudes; the subtropical westerlies were further strengthened, and larger than normal meridional-temperature gradients developed. These led to extremely large vector differences in geostrophic winds and strong westerlies in the middle and upper troposphere. The extraordinary speed of the westerlies extended throughout the troposphere to the jetstream-axis level of 300 mb. For example, at 0400 hours P.s.t., February 13, the observed 300-mb windspeed over 25° N. 130° W. was 110 knots, compared with the February long-term clima- tological average 300-mhb windspeed there of 49 knots (Gray and others, 1976). The observed 500-mhb wind- speed over 28° N. 121° W. at 0400 hours P.s.t., February 14, was 85 knots, compared with the February long-term average 500-mh windspeed there of 29 knots. The geostrophic wind is a good first approximation of upper air wind. A very strong upper level wind can exist only when there is strong vertical shear in the geo- strophic wind from the ground surface to the pressure surface being considered. That is, AV, is large, where AV,, is the vector difference in geostrophic wind between the surface and some upper level. For example, if the upper level is 500 mb, AV, is measured between the ground surface and the 500-mh pressure surface, and is computed as follows: aAV,=- ZC 1413) V.7,Xk, (1) Ps where AV,, =vector difference in geostrophic wind, R,, =gas constant for dry air, f =Coriolis parameter, In =natural logarithm, p, =surface pressure, in millibars, p5 =500 mb, V,, =del-operator on a pressure surface, T,, =mean virtual temperature of the layer, VpTv =virtual temperature gradient on pressure sur- faces integrated through the vertical, and k =unit vector, positive upward. The terms f, R;, p,, and p; are all constant for a specific geographical location and time under consider- ation; therefore, AV,, becomes mainly a function of the mean virtual temperature gradient on pressure surfaces integrated through the layer. The virtual temperature 7,, is defined as T,=(1+0.61 m), where m is the mixing ratio, or the mass of water vapor per unit mass of dry air in the mixture. The mixing ratio is usually numerically small. For instance, at 850 mb over middle-latitude regions, the mixing ratio nor- mally ranges from 0.002 to 0.02. Therefore, for all practical purposes VpTl, in the equation can be replaced by V,,7, which represents the temperature gradient on pressure surfaces integrated through the vertical from the ground surface to the level of interest. For large-scale motion, the mean meridional- temperature gradient determines the average vertical shear of zonal wind, -(dw/ Jp), which becomes -(duldp) with the geostrophic approximation. Here, « and u, are the zonal components of the observed and geostrophlc winds, respectively. When -(du,/dp) reaches a critical value, which is dependent on the other variables, it will lead to long-wave instability. The wavelength of the most intense instability gives the space scale, and the e-fold time of the most unstable wave determines the time scale of the large-scale motion. The severity of the temperature gradient in February 1980 becomes clear from a comparison of the observed meridional-temperature gradients, -(@7/3y)p, which are derived from isotherm analyses at three pressure levels on a sample storm day, February 15, 1980, with the corresponding long-term climatological average -( for the month of February (table 1; all tables at end of report). The observed -(d7/3y)p, in most cases, was substantially greater than the climatological average throughout a wide expanse of the Pacific. The larger than normal meridional-temperature gradient supported a large -(du,/dp), which led to the extremely strong westerlies in the middle and upper troposphere. This large meridional-temperature gradient over the central Pacific sustained vertical shears of the westerlies above the threshold value and provided a favorable environ- ment for generation of short-wave perturbations. The broad circulation pattern immediately preceding the February 13-21 sequence of storms can best be represented by the sectional hemispheric 500-mb analy- ses for 0400 hours P.s.t., February 11 and 12 (fig. 2). At 0400 hours P.s.t., February 11, a strong pressure ridge was over Alaska. West of the ridge, a trough extended from about 50° N. 158° E. to 30° N. 143° W. (fig. 2A). Twenty-four hours later, the ridge took a more north-south orientation (fig. 2B), further impeding the prevailing westerlies. This blocking ridge became the most dominant feature of the upper airflow. A zone of 80° N, 150° E 590 ‘900 s 20° N, 150° E\ \ -'5/_\\\ \§’_\ % o 4. s§ I \\0 A 80° N, 150° E FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 80° N, 90° W (Ey 140° get LQNGWUDE w EXPLANATION -- 570 -- Line of equal height (isobar), in tens of meters --- -5 --- Line of equal temperature (isotherm), 80° N, 90° W in degrees Celsius (°C) L Center of low pressure H Center of high pressure FIGURE 2. -Sectional hemispheric 500-millibar analyses: A, 0400 hours P.s.t., February 11, 1980; and B, 0400 hours P.s.t., February 12, 1980. METEOROLOGICAL SETTINGS 5 large temperature contrast in the central Pacific, as represented by packed isotherms, extended from about 165° W. westward toward the Asian coast. A Low was located at 56° N. 158° E. The temperature around the Low was less than -40 °C, depicting the dome of cold airmass that had originated in Siberia and had been spreading into the central Pacific. The upper airflow was strongly zonal from the coast of Asia to about 160° W. A dominant blocking ridge sat over Alaska and the Gulf of Alaska along 135° W., and a Low was situated to the south at about 35° N. The general circulation westerlies were split either northward to very high latitudes around the blocking ridge or southward to the south of the Low. The subtropical jetstream was routed to a belt between 25° N. and 35° N., as it penetrated beneath the blocking ridge. The baroclinic band over the central Pacific was asso- ciated with the strong vertical shear of the westerlies and long-wave instability. Strong baroclinic instability existed poleward from the jetstream, and a series of short waves developed. The subtropical westerlies strengthened over the eastern Pacific when mean wind- speeds were more than twice the normal along the axis of the jetstream. The Pacific subtropical westerlies were so strong and so extensive that upper level troughs were driven across the Western United States. The troughs weakened the ridge that normally persists there, dis- placed the Great Basin High, and exposed southern California and Arizona to the storm track. Over a period of 9 days, six short-wave troughs were generated in the upper airflow while ecyelogenesis occurred in the lower atmosphere above the ocean surface of the central Pacific between 35° N. and 42° N., beneath the northern side of the jetstream. The sequence of storms during February 13-21, which were identified to the public by numbers, brought heavy rains. DEVELOPMENT OF STORMS, FEBRUARY 13-21 In subsequent sections, a description of the evolution of the storm sequence is followed by an account of the evolution of relevant meteorological parameters and a more detailed account of the meteorological conditions during the first days of the storms. An examination of the events during the first days of the storm period highlights the transition from fair weather and suffices to depict the large-scale meteorological environments in which subsequent individual storms developed. The development and movement of storms are shown in the GOES infrared photography for February 13-21 (figs. 3A-1). The first storm was identified on satellite photography for February 11 as a wave that was developing on an existing cloud band about 32° N. 142° W. (not shown). The wave grew into a cyclone, moved eastward, and spread rain over southern California on February 13. At 0145 hours P.s.t., February 13, the storm had reached the coast of California (fig. 3A). Behind the cold front of this storm were two comma-shaped cloud formations consisting of thick layer-type cloud masses formed from tops of cumulonimbus. Both comma-shaped clouds were related to surface low-pressure centers. By 1000 hours P.s.t., February 13, the storm and cloud formation had extended over all of southern California and western Arizona (fig. 3B). The trailing comma-shaped clouds arrived somewhat later. The second comma-shaped cloud moved inland on the morning of February 14 and across Arizona during that day (fig. 3C). While the Southwestern United States was still under the extensive cloud cover of storm 1, storm 2 was at 33° N. 140° W., to the north of the jetstream (fig. 3B). To the south of storm 2 was an elongated cloud band. This cloud band was representative of a deep airflow bringing tropical moisture to the west coast. The cloud band later merged with the frontal system associated with storm 2, and the low-pressure center had moved in an are north- eastward into central California by the morning of Feb- ruary 15 (fig. 3C). At the same time, storm 3 was identified at 31° N. 150° W. High, cold clouds of subtrop- ical origin between 25° N. and 32° N. preceded the cyclonic center of storm 3, which rotated northeastward toward northwestern California on February 16. The deep layer that continued to bring tropical Pacific mois- ture to the west coast was represented by this cloud mass, which extended from the central Pacific northeast- ward across southern California and central Arizona. The bulging portion of the cloud system, which corre- sponded to the prefrontal system ahead of an occlusion and a warm front at the surface, had moved into Califor- nia and Baja California by the morning of February 16 (fig. 3D). Thunderstorms with a high liquid-water con- tent embedded in the cloud system brought heavy rain. The storm center crossed the coastline late on February 16, and the rains in southern California diminished during the night. The rains in Arizona abated on the morning of February 17. On February 16, the center of storm 4 was visible near 36° N. 155° W in the central Pacific (fig. 3D). The storm was steered eastward by the jetstream, reached the coast of California on the evening of February 17 (fig. 3E), and was accompanied by heavy rain. The rain ended in southern California on the morning of February 18; however, as the short-wave trough moved into Arizona, the rain continued throughout most of the day. This storm brought in a large amount of subtropical moisture as the southwesterly flow from the central Pacific con- tinued. Meanwhile, the freezing level over central Ari- zona had risen from an altitude of less than 5,000 ft (feet) 6 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 34. -GOES infrared image of storms 1 and 2, 0145 hours P.s.t., February 13, 1980. FIGURE 3B. -GOES infrared image of storms 2 and 3, 0145 hours P.s.t., February 14, 1980. METEOROLOGICAL SETTINGS 7T FIGURE 3C. -GOES infrared image of storms 2 and 3, 0145 hours P.s.t., February 15, 1980. y- {fungi 100° FIGURE 3D. -GOES infrared image of storms 3 and 4, 0415 hours P.s.t., February 16, 1980. 8 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 35. -GOES infrared image of storm 4 near the coast of California, 0415 hours P.s.t., February 17, 1980. FIGURE 3F.-GOES infrared image of start of storm 5, 0415 hours P.s.t., February 18, 1980. METEOROLOGICAL SETTINGS o FIGURE 3G. -GOES infrared image of storms 5 and 6, 0415 hours P.s.t., February 19, 1980. FigurE 3H.-GOES infrared image of storm 6 as it moved eastward, 0415 hours P.s.t., February 20, 1980. 10 140 % a ams © W FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 120 FiGurRE 31. -GOES infrared image of storm 6 over Arizona, 0415 hours P.s.t., February 21, 1980. on the morning of February 13 to an altitude of about 10,000 ft above sea level on the morning of February 18. Cyelogenesis north of the Hawaiian Islands led to storm 5. At 0415 hours P.s.t., February 18, that storm was centered at 33° N. 140° W. (fig. 3F). The storm, moving rapidly eastward at about 50 knots, crossed the west coast and arrived over California on the night of February 18. Meanwhile, storm 5 reinforced the rem- nants of storm 4, which was in the form of a trailing cloud band over southern California and offshore waters. This trailing cloud band originated over a relatively warm ocean with sea-surface temperature exceeding 20 °C. A vorticity center also developed and caused showers and thunderstorms over southern California and Arizona on February 19. Storm 6 was a breakoff from a cloud mass 1,000 mi (miles) north of the Hawaiian Islands that occurred on February 19 (fig. 3G). During the night of February 19, the breakoff cloud became disorganized and was seem- ingly dissipated by the westerly jetstream along 35° N. Only scattered remnants of cold, high-top clouds remained. Then a portion of the seattered clouds merged, and growth renewed. The cold cloud-top area enlarged rapidly over a period of several hours while moving toward the coast. At 0415 hours P.s.t., February 20, the cloud-top area was centered at 34° N. 129° W. (fig. 3H); it reached the coast in the afternoon and evening. Because of the lack of a well-organized cyclonic cirecula- tion, storm 6 entrained less moisture than the previous storms. Intermittent moderate to heavy rain was observed over southern California and central Arizona until the afternoon of February 21 (fig. 31). A ridge of high pressure had developed over the central Pacific by February 21 and diverted subsequent storms to a more northerly track; the next storm approached the west coast of Oregon north of 40° N. RAINFALL POTENTIAL The most important factor that influences precipita- tion from a storm is the availability of an adequate moisture supply. The moisture supply is measured as inches of precipitable water. Large amounts of precipi- table water were maintained over the study area throughout the storm period. Amounts of precipitable water in the layer between ground surface and the 500-mbhb pressure surface at Vandenberg Air Force Base, Calif. (northwest of Santa Barbara), San Diego, Calif., and Tucson, Ariz., are shown in figure 4. A second factor important to many storms is the degree of instability, which is indicated by the K index and the lifted index. The K index is a measure of thunderstorm potential based on the vertical tempera- ture lapse rate, the moisture content of the lower atmo- sphere, and the vertical extent of the moist layer. An index of less than 15 corresponds to a thunderstorm probability of zero percent. As the index increases, the METEOROLOGICAL SETTINGS 11 1.00 0.90 o to o 0.70 0.60 PRECIPITABLE WATER, IN INCHES o in o 0.40 0.30 0.20 12 13 14 15 16 17 18 FEBRUARY 1980 19 20 21 22 EXPLANATION PRECIPITABLE WATER-Data based on soundings at 0400 P.s.t. Points are unconnected where data between points are missing. ®@--@ San Diego, California O---O Vandenberg Air Force Base, California A--A Tucson, Arizona FIGURE 4. -Evolution of precipitable water, February 12-22, 1980. probability increases until the index reaches 40, at which level the thunderstorm probability approaches 100 per- cent. The lifted index is computed by theoretically lifting a parcel 25 mb above the surface dry adiabatically to the lifting condensation level and then moist adiabatically to 500 mb. The observed temperature at 500 mb minus the parcel temperature is the lifted index. A lifted index of 4 or less indicates unstable conditions; values above 4 indicate stable conditions. A highly negative value indi- cates that the energy required to lift a parcel of air to its level of free convection is much exceeded by the positive energy released by the parcel between the starting level and 500 mb. Therefore, convection will be self-sustaining once a parcel has passed the level of free convection. A high stability criterion does not preclude convective precipitation. The stability indices can be calculated only for stations in the radiosonde network where tempera- ture structure and moisture content are measured. The average spacing between such stations is about 200 mi, and the time interval between soundings is 12 hours. The 40 T T T T T K INDEX -40 I I | | 1 I | | I | 12 13 14 15 16 17 18 19 20 21 22 FEBRUARY 1980 EXPLANATION K INDEX-Data based on soundings at 0400 P.s.t. Points are unconnected where data between points are missing. ®@--@ San Diego, California O---O Vandenberg Air Force Base, California A---/ Tucson, Arizona FIGURE 5. -Evolution of K index, February 12-22, 1980. typical convective cell has a dimension of 6 mi and a life of 1 hour; therefore, convective storms can occur when indices indicate a stable atmosphere. The tenuous rela- tionship between the lifted index and rainfall shown in figure 6 bears this out indirectly. The evolution of the K index and the lifted index during the storm period is shown in figures 5 and 6, respectively. The lifted index indicated unstable condi- tions over southern California on February 14, 15, 17, 19, 20, and 21. Unstable conditions existed over Tucson, Ariz., on February 13, 15, 17, 19, and 20. The changes in moisture and stability parameters for San Diego and Tueson prior to the onset of the storms is typical of what happened over much of the study area. At San Diego, precipitable water at 0400 hours increased from 0.22 in (inch) on February 12 to 0.83 in on February 13 and 0.96 in on February 14. (The mean of the semimonthly maximum is 0.80 in, and the maximum observed semimonthly value over 27 years of record is 1.28 in.) During the 24-hour period ending at 0400 hours 12 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 16 A 1 1 \ Q1 7 x A 1 \ 1 o in ’// A / # \ /_T’A§ - s If, \ 0 4 \ A 4 w - T . J o 1 k u A f g C 1 Ci -i 1 Fg \ C \ [I 2 - \ 7 |- ¥ ‘ _ -4 |_ _ -6 | I 1 I I 1 1 I | I 12 13 14 15 16 17 18 FEBRUARY 1980 19 20 21 22 4 29 TTT -t --t --t --t --t --- E; 1.5 |- - San Diego, California in $3 10 |- - 2st lpn l..] - o 0 f a T ot if oso fu I fcr 12 13 14 15 16 17 18 FEBRUARY 1980 19 20 21 22 EXPLANATION LIFTED INDEX-Data based on soundings at 0400 P.s.t. Points are unconnected where data between points are missing. ®@--@ San Diego, California O ---O Vandenberg Air Force Base, California A «--A Tucson, Arizona FIGURE 6.-Evolution of lifted index at three locations, and daily rainfall at San Diego, Calif., February 12-22, 1980. on February 13, the K index increased from -30 to +28 and the lifted index decreased from 14 to 10. The extreme change in the K index of 58 in 24 hours indicated a drastic shift in the nature of the airmass from a very dry and stable thermostructure to a structure with high moisture content below the 700-mbhb level. A K index of 28, by itself, would show a 50-percent probabil- ity of thunderstorm occurrence. A K index of 28 com- bined with a lifted index of 10 (fig. 6) indicated a thermostructure that inhibited free convection. A rain- fall of 0.01 in between 0400 and 0500 hours on February 13 at San Diego was followed by moderate rain beginning about 0900 hours. The earlier rain most likely came from layer clouds associated with an extratropical cyclone. Precipitable water at Tueson increased from 0.23 in on February 12 to 0.66 in on February 13 and 0.82 in on February 15. (The mean of the semimonthly maximum is 0.54 in, and the maximum observed semimonthly value over 21 years of record is 0.89 in.) The prognostic K index and 700-mh 12-hour net verti- cal displacement at 0400 hours on February 14 are shown in figure 7. Over most of southern California the net vertical displacement was an ascent of more than 50 mb in 12 hours, and over most of Arizona the ascent exceeded 80 mb in 12 hours. The latter is approximately equivalent to a net rising of 900 m (meters). Significant rising motion on a synoptic scale provided a favorable environment for individual convective cells to develop within the large extratropical cyclone. The prognostic K-index value exceeded 32 over the study area, and it exceeded 36 over a limited area. These high indices indicated a thunderstorm probability of 70 to 85 percent. The available observations of stability indices indicated reasonable agreement between observed and forecast yields. Interpreted trajectories of air parcels for three pres- sure levels-surface, 700 mb, and 850 mb-at Phoenix at 0400 hours on February 14 are shown in figure 7. A region of the Pacific Ocean just off Baja California, in which sea-surface temperatures between 18 and 22 °C were observed in mid-February 1980, was a significant source of moisture for central Arizona. Moist maritime air from that region was brought directly into Arizona by the southwesterly flow without passing through south- ern California. The average relative humidity from the surface to 500 mb and the instantaneous vertical velocity at the 700-mb level at 1600 hours on February 13 and at 0400 hours on February 14 are shown in figure 8. At both times, relative humidity exceeded 70 percent over the study area. Vertical velocity exceeded 2.24 em/s (centimeters per second) over southern California. Over central Ari- zona, vertical velocity was positive, but was smaller than 2.24 em/s at the first sampling time and greater than 2.24 em/s at the second. At 0400 hours on February 14 a 500-mb trough approached the study area. Rising motion on the lower troposphere over the study area was associated with the passage of storm 1. BEGINNING METEOROLOGICAL CONDITIONS, FEBRUARY 13-14 Meteorological conditions at the beginning of the storm sequence are represented by surface air and upper air analyses at 1600 hours on February 13 and at 0400 hours on February 14 (figs. 9-12). The 300-mbh analyses (fig. 9) showed that the subtropical jetstream was located between 25° N. and 30° N. over the eastern Pacific and passed over Baja California, northern Mexico, and south- eastern Texas. The jetstream meandered during the 9-day storm period; its most frequent position was over Baja or southern California. At 126° W., windspeeds along the jetstream at 0400 hours on February 14 METEOROLOGICAL SETTINGS 13 -I 3/99 ,6°/ \0 $6 © T_ _ 9 l f\\ | EXPLANATION LQ} vommmmmes Line of equal displacement of the 700-millibar pressure surface-Positive values indicate a rising pressure surface; negative values indicate a sinking pressure surface. Interval 20 millibars wees sam» 32 «« <-- _ Line of equal K index-Interval 4 units Trajectory of air parcels arriving at Phoenix, Arizona / I\ Surface // ------ At 850-millibar pressure surface /—— At 700-millibar pressure surface FIGURE 7.-Net vertical displacement of the 700-millibar pressure surface during the 12-hour period ending at 0400 hours P.s.t., February 14, 1980, and K indices and trajectories of air parcels at the ending time. reached 120-130 knots (140-150 mi/h (miles per hour)), which is more than twice the climatological normal. This strong subtropical jetstream drove the upper level troughs across the Western United States, weakened the normal mean ridge, and displaced the Great Basin High over Nevada and Utah. The High had been the primary obstacle blocking the storm path into southern California. As a result, Pacific storms were permitted to invade southern California and Arizona. The meteorolog- ical settings were very similar to those associated with the sequence of four major storms of January 1969, which inundated southern California. Storm centers were generated continually over the central Pacific beneath the northern side of the jet- stream. An example of such a storm center was the Low centered near 32° N. 125° W. at 1600 hours on February 13, which was apparent at all levels from 500 mb to the ground surface (figs. 10A, 114, 124). At 1600 hours on 14 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA Lora £3 a ss | ~ EXPLANATION Area where mean relative humidity exceeded 70 percent -- _ Line of equal upward velocity-Interval 2 microbars per second -- 30-- Line of equal mean relative humidity from surface of Earth to the 490-millibar pressure surface-Interval 20 percent FIGURE 8. -Analyses of relative humidity and vertical velocity: A, 1600 hours P.s.t., February 13, 1980; and B, 0400 hours P.s.t., February 14, 1980. METEOROLOGICAL SETTINGS 15 A 140° 120° 100° 80° B 140° 120° 100° 80° EXPLANATION E Area where windspeeds were between 70 and 110 knots Ny . {fag Area where windspeeds exceeded 110 knots '§§>‘}31‘5%§' - -~30 -.- Line of equal temperature (isotherm), in degrees Celsius --- 10K --- Line of equal windspeed (isotack), in knots --- 900 «=== Line of equal height (isobar), in tens of meters, showing altitude above sea level where atmospheric pressure equals 300 millibars L Center of low pressure FIGURE 9. -300-millibar analyses: A, 1600 hours P.s.t., February 13, 1980; and B, 0400 hours P.s.t., February 14, 1980. 16 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA A 140° 120° 100° 8o° ( Eb 720, 4540 SF L _" ‘i Q/ l 516 z a e 8 2 40 1 g° Sl~C \ 52 a 2 % 5% 5347 5 \ - 4 3 540 T =-- comms / [~ 6 a = mur =-- 30, 54 552; A ~- one 552 pipa l= = > 25 7 - ~ 564 30° -~ a 558 51°, ~20 546 a w w - 2o "4 3, LJ*~ 18 \\ cis 16 58, x 7 b I7 ~- se Z~ ~- // 0 20° " .es 30 f / 0 510 576 p 70\ aoe am L * mean io _ -* \ 531 /5/ ~. mcd _c B 140° 120° 100° 8o° e w 2 54 540 - 55. S> _ 35 & ( @ / aP 5347) - 4 516) 528 ao° s46 [. 22528 ~' 407 3 522 §#1 A reused 0 XZ -C z gA 3 534 z 5, fae p m -ur Crea. * - 6 % 5527 -25 556i” To, / 6 0/1 * amy AOA mp -20 6 $552 gp z o 40 516 Prs. /Z py * fig'l -" Fez - yr ~ 15. // G~ 20° 570 7" f 516 -~ ==-- 22 ___ S /<3 \H 582 ~ EXPLANATION -- - -10 ---- Line of equal temperature (isotherm), in degre es Celsius 552 Line of equal height (isobar), in tens of meters, showing altitude above sea level where atmospheric pressure equals 500 millibars L Center of low pressure H Center of high pressure FIGURE 10. -500-millibar analyses: A, 1600 hours P.s.t., February 13, 1980; and B, 0400 hours P.s.t., February 14, 1980. METEOROLOGICAL SETTINGS A 140 120° 100° 8o° U U Ig 74 LT o QV ( 144 L 60x N 6 p & f 7" 4 * f 135 40° \ A& t> 138" J & \ a,» ea im -155 135, 1 m ~ -_ 15 1752 w— 5\ A-) ~ _ 10 -B _515/ \\ ‘53/ I2 \ 5. x. 0 f 30° W w. _/ &~ ~- 132, 10-£L_ 8 --k2 / ¢ | - 15. -~ w 107 135 -~ © o I A $9 p 138 ) P - 20° -* 15 141 8 ° k " A § ~* ® A Nw £3 / ~- 15 ‘E CoC Z Filing»... Pc B 140° 120° 100° 8o read ~ 2p | "I41--f the \z 4 f L 22 \ -20 % 135 A ° 3 a t\% -~; 75 40° o\ o N 39 s - N ap s -25 7 141 \A" 4 A 1447 L-- 0 L -10 44 \\\ 13\2 \ ee., -* c 604 $\ \\ -15~ -5 A *~ Pa f To _ 1 -10 ge- 15 ho \ ~. # pae "e 0 7l 30° \ \\ ~ A \0 __ (367‘ Mes L A N9— *s 5 i , 5 - \\ 72, \\ bung Q? 10 65 ~- ( 8. ~ 7 _ Ct ,147 \ \ A7 \\\ 97, 10 --- ao 4g 150 -* " ~ # ~ * ( / - 15 - 20° 747. ~ [yom 0/ e' // 156=1] 0 ! je T= O1 mus ~ _u ~ 15 \\\ EXPLANATION -- - 19 -- _ Line of equal temperature (isotherm), in degrees Celsius 141 Line of equal height (isobar), in tens of meters, showing altitude above sea level where atmospheric pressure equals 850 millibars L Center of low pressure FIGURE 11. -850-millibar analyses: A, 1600 hours P.s.t., February 13, 1980; and B, 0400 hours P.s.t., February 14, 1980. 18 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA A 140° 130° 120° 110° 100° B 140° 130° 120° 110° 100° WNL V WI T V 12 G’\ & 12 LT s & Ls, & 3 \a ~ x, o xs 8 2 &. 8 C dr 4 4° 4 t-ob 40° 0 I ‘l -24 \285 4A S-20 < \ A 0 24, a & 4 2 \ -4 p l' 76. " 30 L | 30 _6 L U 12 / 0, L8 ¢ z s ~ror " e ~* 0 8 4 20° 20° 8 12 12 XV \ 76 S / \- 20 EXPLANATION 4 Line of equal pressure (isobar), in millibars above or below 1,000 millibars ---TROF --- Low-pressure trough _A___A ___A. Cold front-Movement is in direction of points -&-y-&-w- _ Stationary front L -g Center of low pressure-Number is pressure in millibars above or below 1,000 millibars FIGURE 12. -Surface analyses: A, 1600 hours P.s.t., February 13, 1980; and B, 0400 hours P.s.t., February 14, 1980. February 13, the surface cold front of storm 1 was progressing eastward through southern California, which was then under a 500-mh trough-to-ridge contour pattern. An absolute vorticity maximum (not shown) with a magnitude greater than 14% 10~> was just off the coast, indicating that strong positive vorticity advection into the region could be expected. On the 850-mb surface (fig. 11), the deep trough off the coast of Baja California facilitated a southwesterly flow of moist maritime air over southern California and Arizona. The blocking ridge and High were positioned over Alaska and the Gulf of Alaska. This is a typical location for a high-latitude, warm anticyclone, with temperature in the High greater than the surrounding environment at all levels from 850 to 300 mb. Above 300 mh (the tropopause) (fig. 9A), the temperature gradient reversed, and temperatures in the High were lower than those in the surrounding environ- ment. The accumulated airmass in the lower strato- sphere overcame the density deficiency in the tropo- sphere, and the High and the ridge were maintained. The persistent ridge of high pressure blocked the zonal circulation and divided it into two branches, as men- tioned earlier. The jetstream followed the northern route as late as February 11, while the subtropical westerlies over the Pacific were weak. On February 12 and 13, the subtropical westerlies strengthened greatly, and a sub- tropical jetstream formed. The subtropical jetstream penetrated "beneath" the Alaskan ridge and pulled the storm track southward. The 500-mb short-wave trough (fig. 10) associated with storm 1 was at approximately 122° W. at 1600 hours on February 13. This short wave progressed eastward through the basic long-wave pattern and was just off the coast of southern California and Baja California on the morning of February 14. Meanwhile, a new cyclone was growing offshore. The low-pressure center of storm 2 was located at 33° N. 138° W. at 0400 hours on February 14 (figs. 9B, 10B, 11B, 12B). The Low extended through 850 mh and was reflected on the 500-mb level as another short-wave trough. The short wave associated with this Low again moved rapidly through the long-wave pattern and PRECIPITATION DISTRIBUTION 118° a2° | | | | 116° 114° 112° 110° 19 ~-. _ ~ -_. _. NORTHEAST INTERIOR BASINS 40° |- SACRAMENTO DRAINAGE 38° |- San Francisco SAN JOAQUIN DRAINAGE A, |= -t -t | \, i ® [- ~. 10.8 ARIZONA ~ « & s ToS" _P -] R A l 1g NORTHEAST C Bakersfield ‘\ ‘k <> SOUTHEAST \\ U o o Flagstaff DESERT ”\ Kingman BASINS \ o "L _J-/~] CENTRAL _| / 200 MILES 32° - 0 100 200 KILOMETERS | | © Phoenix CENTRAL g Tucson t. SOUTHEAST ~ FIGURE 13. -Climatic divisions in California and Arizona. propelled the Low toward southern California; mean- while, the long-wave trough off the coast was almost stationary near 130° W. Variations of the sequence of events described for storms 1 and 2 were repeated as subsequent storms developed on the polar side of the jetstream over the central or eastern Pacific in the 30° N. to 42° N. latitude belt and moved toward the coast of California. PRECIPITATION DISTRIBUTION Rainfall over California during the 3 months ending December 31, 1979, was not excessive. Average precip- itation during the period ranged from a high of 127 percent of normal over the North Coast Drainage cli- matic division to a low of 22 percent of normal over the Southeast Desert Basins climatic division (fig. 13). In December, the South Coast Drainage climatic division had an average precipitation of 0.70 in, which was 28 percent of the normal December average for that divi- sion. Rainfall over Arizona during the last 3 months of 1979 was less than normal. It ranged from 94 percent of normal in the Northeast climatic division to 19 percent of normal in the Southwest climatic division. Average pre- cipitation during December 1979 for the South Central 20 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA and North Central climatic divisions was 0.19 and 0.63 in, respectively. These values are 17 and 483 percent of normal December precipitation. Two significant storms struck California and Arizona in January 1980. The first occurred January 7-19 over California and January 9-22 over Arizona. Rainfall, often heavy, was recorded at most reporting stations in Cali- fornia for 10 consecutive days. This storm was warm and produced rainfall in the Sierra Nevada at elevations as high at 9,000 ft. Rainfall was reported over most of Arizona each day during the period January 9-22, except January 16. The second storm occurred January 23-31 over both States. The January precipitation at many stations in the two States was much above normal. Amounts of precipitation at selected stations shown in figures 14 and 15 are given in table 2. Average amounts for the various climatic divisions are given in table 3. The January 1980 mean precipitation in all climatic divisions, except in the North Coast Drainage division of Califor- nia, greatly exceeded the normal. In California, the highest percentages of normal occurred in the South Coast Drainage and Southeast Desert Basins divisions; in Arizona, the highest percentage occurred in the North Central division. The respective percentages for these three divisions are 298, 239, and 442. These three climatic divisions also received the highest above-normal precipitation in February (table 3). In California, the South Coast Drainage and Southeast Desert Basins climatic divisions had February amounts of 413 percent and 374 percent of normal, respectively. In Arizona, the North Central climatic division had 562 percent of normal. Precipitation over California and Arizona was negligi- ble during the first 6 days of February. The North Coast Drainage climatic division of California had an average rainfall of 1.5 in, the Sacramento Drainage climatic division had about 0.5 in during February 7-9, and the Southeast division received 0.75 in during February 8-9. Otherwise, the period February 1-12 was dry. The six storm systems of February 13-21 brought above-normal precipitation to large areas in California, Arizona, New Mexico, Nevada, and Utah. Occasionally, wet conditions extended farther east. Southern Califor- nia and central Arizona received more precipitation from this sequence of storms than did other areas. The effect of orography on the distribution of precipi- tation was significant. In southern California, the coastal plains and valleys received an average of 5 to 10 in, while most stations in the coastal mountain ranges had more than 15 in and a few stations had more than 30 in. Los Angeles Airport and Los Angeles Civic Center in the coastal plain had 9.37 and 12.75 in, respectively (fig. 14). Mount Wilson 2 had a storm total of 30.71 in, and Crestline Fire Station had 30.10 in. The 30.89 in at Lytle Creek Ranger Station was the largest total precipitation on record for the month of February in California. In central Arizona, terrain dependence was reflected by the fact that 10 in or more fell in a band approximately parallel to the Mogollon Rim (fig. 19), which extends diagonally across central Arizona. Heaviest precipitation fell over the headwaters of the northern tributaries to the Salt River. Compared with southern California, storm precipitation over central Arizona was usually of less intensity and shorter duration, and had longer intervening breaks. Rainfall amounts ranged from 1-3 inches in the extreme south, west, and northeast to 3-12 in over the central basins, Mogollon Rim, and White Mountains, at the head of Black River, a main fork of Salt River. The most rainfall recorded in Arizona was 16.63 in at Crown King, 55 mi north of Phoenix in the Bradshaw Mountains (fig. 15). The amount was 0.32 in less than the record monthly amount for Arizona, which occurred at Crown King in August 1951. At higher elevations in Arizona, part of the precipita- tion became snow. GOES data indicated that 14 percent of the Verde River basin was covered with snow on February 12, and that 26 percent was covered on Feb- ruary 23. The corresponding coverages for the upper drainages of the Salt River were 19 and 23 percent. The water contents of snow cover were measured by the SNOTEL (SNOw-survey TELemetry) data system operated by the U.S. Soil Conservation Service at 15 snow courses in the Salt River basin, 16 in the Gila River basin, and 17 in the Verde River basin. The average water equivalent of the snow cover increased substan- tially during February, particularly during the latter half of the month. The average water equivalent of the snow cover in the Salt River watershed increased from 6 in on February 1 to 6.75 in on February 15 and 10.5 in on March 1. The average water equivalents on these dates were 7.0, 7.5, and 9.6 inches in the Verde River water- shed and 4.8, 5.6, and 7.2 inches in the Gila River watershed (U.S. Soil Conservation Service, 1980). At three individual snow-survey courses, the increases in the water equivalents of the snow cover exceeded 15 inches in February. The facts suggest that most of the storm precipitation in the high mountains fell in the form of snow, was retained as snow, and made no contribution to the flood runoff. The storm series also affected the normally arid region between the major precipitation centers in coastal south- ern California and central Arizona. This arid region consists of the southern deserts of California and the Colorado River Valley and lies in the lee of the southern California coastal mountains. Storm rainfalls over this arid region were an order of magnitude smaller than those over the coastal plains and mountains but were very significant compared with local precipitation PRECIPITATION DISTRIBUTION 21 119° 118° 117° 116° | | I 0 MOJAVE | | 35° |_ i | K E R N . | f DAGGET ege s ops ean nees. f ¢ p | \ | \ PALMDALE | s $ | 5 A N BERNA R DIN 0 ap) ‘ | - \ _ _LOS ANGELES | a \ | LyTLe CREEK RANGER STATION -> \ MT WILSON 2 SAN GABRIEL! PUMPING PLANT. Q / TOPANGA P ATROL ‘ PASADENA 1 CRESTLINE FIRE STATION "_ STATION UCLA / OSan Bernardino O Los Angeles _ { 3° \& Los angeles / _ “of“? ------- mcm * L =z CIVIC CENTER |----s_ _| Riverside Los ANGELES ,/ _ \‘€ AIRPORT ‘TORRANQE _ ‘PALM SPRINGS LONG BEACH *, RIV E RSID E *~ _ ~ A 3-4 PALOMAR MT f OBSERVATORY | 0 HENSHAW DAM i | | > S A N DIE G O p g ‘CUYAMACA I - 2 t _I] Area of map » | < LA MESA s 6 1 2 EXPLANATION San Diego | 3 Climatological station and name / CHULA VISTA CAMPO p' M SAN DIEGO 6 "2. L2 lke. e=" 0 20 40 MILES 0 20 40 KILOMETERS FIGURE 14. -Selected climatological stations in southwestern California. 22 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 114° 113° 112° 111° 110° T T T T T B90 fe uke nnn nne ee a e eee e en np nna es asp nenas ames n ons o egen men noni po- I 1 § t I 1 1 ® I 1 1 | C & i | G I I é" I<" | 6/9 f I $ € i€/ i -. I NEVADA 1 fe 2 | ig i ph 1 2 | TUWEEP, T 2 q (* | 1 0 I | 50 om i ovogfivo \ Moen—kogs E // E EM : M O H AV E \ le 1 _/ | O : 5 Ca 1 ( > 4 | A a o 14 ( I c oC.C O N I N) 0 |/ | < i boy ® "& Koos Fp o \ \ a jA ( A I TRUXTON b Ok g ~ ", €} > i «o 21 \ CANYON A } &FORT VALLEY LCC / | < i we) G \ @ Kingman j 3 ~ u: @ Flagstaff If E /?s\/ I 7004 "1 1 Z |_ 32" f 35° |- ( I I @winstow __ | $7" | NEEDLES \ i @sunipine ; w ln 1 3 E 1 Holbrook 3 l e JEROME I---4 ' | \ \<. | Y A V A P Y¥A\I I 4 ( River , i ) f PRESCOTT I a . ; ; 1 ewe Prescott > Ir3 . E E St Johns @ 1 C. mo ~ ( 2 | | | in JS WALNUT 4 MAYER Felt t w l i 1 Bill w I CALIFORNIA ' i GROVE? 3NNW CHILDS Jake i e PARKER [ PAYSON 0 0 PueAsANt i 10 ago |- ( -' crown, VALLEY i l arm's: -& ___ king /~~~--& m? ''''''''''''' T 1 ; WIKENBURG | ~€ BARTLETT § \ Roosevelt River : I “JI 5 | ¢ DAM a c UT. Ck o a Iom a /r Ijc o P{faA A h. o n ! j 1 @ it MORMON FLAT t i i i / Phoenix C \ 2 Miami | -_- i =| Y U M A f | < PHOENIX : \@ocive (* | Zl i \y AirPort? | \ ® i m i Rene -~ SUPERIOR \ PD p curron 2 = | 1 ; \ H Te, 33° |- “five“ E Til F Florence A a M * lim l. i Cal FLORENCE < J G R AMM A M\\ oi ( z i Yuma ol* | i COP I N A L \ : Safford © * 3. ket & f R ~. Mg 1 * 1 I A 'O, | DUNCAN YUMA f I *n, C. 1oa *a, ds aoe me ms mt ii me a nah wa aiuto mri he i mes tals man 1 \\| lho e i @ aso PALISADE RANGER STATION & 1 \\~\ H \ | $19; | ~s._ i Tucsodp " SABINO @ 1 tal Tucson AirPoRT&p CANYON / I ~J 1 32° |- ~. ke i ~~. im | % ~ Po I M- A 3 |- _& ~*, A I eVYo c wos oe | o 25 50 MILES ~-._ worn do | psc di ~~. 1 santa 100 \ i ~~. (7a I \ 0 _ 2500 50 _ 75 KILOMETERS *~. CRUZ -| * atms I l\\~Nogales \ t J ° ___: | |__ | 1 EXPLANATION 0 Climatological station and name FIGURE 15. -Selected climatological stations in Arizona and southeastern California. PRECIPITATION DISTRIBUTION 23 climatology. Needles, Calif. (30°%50' N. 114°35" W., fig. 15), recorded 1.21 inches in February, or 378 percent of normal; Dagget, Calif. (34°52' N. 116°47' W.), had 1.76 in, or 490 percent of normal; and Mojave (85°03 N. 118°10' W.) received 4.25 in, or 421 percent of normal. Yuma, Ariz. (82°40' N. 114°26' W.), had a February total of 0.37 in, or 270 percent of normal. All the aforemen- tioned precipitation fell February 13-21. A study of radar summary maps of the Western United States (fig. 16) indicated that the precipitation patterns were quite persistent with respect to time over central Arizona and part of the southern California coastal mountains. Radar can be used to show the areal extent of rainfall and some degree of gradient in precip- itation, but the maps do not provide a reliable measure of intensity or depth. Estimates of depth from radar have large systematic errors. Radar measurement of precipi- tation is based on the premise that rainfall intensity is a function of the radar-reflectivity factor. The radar senses a volume-integrated reflectivity of the precipitation pat- tern in the atmosphere. It provides a means of estimat- ing rainfall intensity over an area of up to 10° mi" (square miles) with a resolution of 1 nautical mile by 2° azimuth angle. The conversion of the reflectivity factor into rain intensity is determined empirically as a function of drop-size spectrum. This relationship is affected by geog- raphy, observational duration, and types of rain (strati- formis, thunderstorm, or orographic). There are many different Z-R equations (relating rainfall rate, R, to drop-size spectrum, Z) published in the literature based on regression studies at a variety of locations, during different seasons, over varied durations, and for partic- ular types of rain. No single equation fits all situations. An accurate measurement of point rainfall is obtained only from a rain gage, but the gage does not define the areal pattern of rainfall. The areal pattern obtained by analyzing all available gage data for a specific storm is affected by the density of the gage network and the reliability of reports. It would be fortuitous for any gage to capture the maximum rainfall that occurred during any given storm. The optimum method for combining the accuracy of point rainfall given by rain gages and the areal pattern given by radar in order to arrive at a more accurate representation of rainfall in relation to space and time remains an unresolved problem and is the topic of much research. As for rainfall depth, the Video Integrator and Pro- cessor (VIP) component of a weather radar system, level 1 corresponds to a precipitation rate of up to 1.1 in/h (inch per hour) for convective storms. Considering that in synoptic observations any rate greater than 0.3 in/h is classified as "heavy" precipitation, VIP level 1 thus covers the whole spectrum of synoptic rainfall intensities from drizzle up to extremely heavy rain. Such a coarse classification is inadequate for many quantitative appli- cations. Precipitation mass curves for selected stations are shown in figure 17. The mass curve for Crown King, Ariz., was derived from curves for Mayer 3 NNW and Payson, for which hourly data were available. Precipita- tion contributed by each storm in the sequence is indi- cated on four of the mass curves, by storm number. Generalized isohyetal analyses of total precipitation during February 13-21 for southern California and cen- tral Arizona are shown in figures 18 and 19. Storm precipitation amounts for 1-day and 10-day periods at selected stations are compared with 100-year events in table 4. Wherever hourly data were available, the 24- hour maximums are listed; otherwise the 1-day values are used in the comparison. The maximum observed 1-day total at Palisade Ranger Station in the Santa Catalina Mountains near Tucson of 4.83 in was the highest 1-day total in Arizona during February 1980. At all other stations, including Topanga Patrol Station northeast of Los Angeles, where the greatest 1-day rainfall in California in February 1980-8.30 in- occurred, the daily maximums were much smaller than the 100-year amounts. The 10-day total precipitation (February 13-22) is approximately equal to, and for seven stations greater than, the 100-year 10-day amounts (Miller, 1964). Comparisons of maximum storm rainfall over dura- tions of a day or less with total rainfall over a 1- or 2-month period are revealing. For example, Janu- ary-February total rainfall at Cuyamaca, Calif., was 45.27 in, the highest since recordkeeping started in 1888, and February rainfall-23.34 in-is the third highest of record, but the maximum 24-hour rainfall of 5.90 in is about equal to the 5-year 24-hour rainfall. The maximum 6-hour rainfall of 3.1 in also has a 5-year recurrence interval (Miller and others, 1973). At Los Angeles Civic Center, the February rainfall of 12.75 in is the second highest in the month of February since recordkeeping began in 1872; a rainfall of 13.37 in occurred in February 1884. The combined January-February rainfall of 20.25 in is also the second largest, exceeded only by the 22.97 in during January-February 1969. The 1-day maximum of 3.03 in that was measured during the storm period is less than the 5-year daily amount of 3.81 in. At Henshaw Dam, the February rainfall of 21.40 in is the second largest since the beginning of recordkeeping in 1912, and the combined January-February rainfall of 35.94 in is the largest; however, the daily maximum of 3.85 in is a 5-year rainfall. At University of California, Los Angeles (UCLA), in west Los Angeles, the February 1980 rain- fall of 18.37 in is the highest since recordkeeping started in 1933 and exceeded the magnitude of the 200-year event. The combined January-February 1980 rainfall of 24 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA A 125° 120 ° 115° 110° B 125° 120° 115° 110° EXPLANATION E Area of radar echo 130 - Altitude above sea level of cloud top, in hundreds of feet QM Direction and velocity of echo movement-Arrow indicates direction. Tail bars indicate velocity; each long bar equals 10 knots, and the short bar equals 5 knots --» 15 Direction and velocity of individual cell movement-Arrow indicates direction; number indicates velocity, in knots R Rain RW Rainshowers S Snow TRW Thunderstorm rain shower SW Snow shower LM Little movement STC Light precipitation may be detected FIGURE 16. -Radar summary maps, February 14, 1980: A, 0635 hours P.s.t.; and B, 1335 hours P.s.t. CUMULATIVE RAINFALL, IN INCHES CUMULATIVE RAINFALL, IN INCHES Brandy Creek, CA (40°37'N 122°34'W) T T T T T T T PRECIPITATION DISTRIBUTION Crestline Fire Sta 2, CA (34 °14'N 117 °18'W) T Palomar Mt Observatory, CA (33°21°N 116°52'W) :- ror-ror-r-t 24 T T T T T T T T 30 |- 30.10 | 23.10 22 |- | - gh 1 Los Angeles Civic Center 20 |- - 4 (34°03'N 118 °14'W) | 16 t t t t T t t t u 18 |- | | { - J 14) B 16 |- L | | 12 |- ~ 14 |- |- { { 12} I | 10 f 1 { 10 }- g |- | 4 8 |- L | 4 6 } 4 6} - { { L J 4} 4 4 |- - 2} L g | { 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 0 13 14 15 16 17 18 19 20 21 22 13 14 15 16 17 18 19 20 21 22 13 14 15 16 17 18 19 20 21 22 13 14 15 16 17 18 19 20 21 22 FEBRUARY 1980 FEBRUARY 1980 FEBRUARY 1980 FEBRUARY 1980 Cuyamaca, CA (32°59'N 116°35'W) 26 -r -r-- boob u 1 Payson, AZ (34°14'N 111° 20'W) 10 t T- t t t t t T 8 } 6} 1 Crown King, AZ (34°12'N 112°20'W) popa u u 1 Clifton 17 NE, AZ 25 109 °12'W 12 t t t t t t t t t 10 4 6 8.50 8 (no rain at 5 | station) 6 I 4 | 2 { 1 1 1 1 1 1 1 19 20 21 0 13 14 15 16 17 18 FEBRUARY 1980 22 13 14 15 16 17 18 19 20 FEBRUARY 1980 1 i 21 22 o 1 13 14 EXPLANATION 3 - Storm number- Indicates amount of rainfall received during that storm i 20 15 16 17 18 19 FEBRUARY 1980 16.63 Total amount of precipitation received at the station 21 22 13 14 15 16 17 18 19 20 21 FEBRUARY 1980 FIGURE 17. -Precipitation mass curves for selected stations in southern California and central Arizona, February 13-22, 1980. 25.72 in also established a record for the 2-month period; however, the observed maximum daily rainfall of 4.14 in is less than the 5-year amount. Similar situations can be found in records for many other stations in southern California and central Arizona. 22 It can be concluded that the February 1980 floods in southern California and central Arizona were caused by the cumulative effect of precipitation events, each of moderate and occasionally high intensity, and not by extreme rainfall of short duration. Examination of 26 120° 119° FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 118° 117° 16° I I 35° CG] SANTA BARBARA SANE A5 - BERNARDINO 40 A \ ‘i * » C2 [¥ Y L; EXPLANATION -10- Line of equal precipitation-Interval 5 inches m Population centers Mountain ranges FIGURE 18. -Isohyetal analysis of total storm precipitation greater than 5 inches in southern California from approximately 0600 hours P.s.t., February 13, through 2400 hours P.s.t., February 21, 1980. NOAA hourly precipitation data further revealed a lack of extreme events with durations of 1 to 24 hours, a characteristic that has been recognized as associated with winter precipitation brought about by extratropical cyclones. CALIFORNIA FLOODS Storms of January and February 1980 caused three distinct periods of significant flooding over most of California; each period affected different areas of the State (fig. 20). The storm of mid-January covered the entire State, but most of the flooding was caused by runoff from the Sierra Nevada and the Sierra foothills. Subsequent storms affected primarily southern Califor- nia and coastal areas northward to San Francisco. On many streams in southern California the floods of late January or mid-February are the highest since either 1927 or 1938. The February floods are the most costly of any that have occurred in southern California. The main emphasis of this report is on the February floods in coastal basins south of 35° N. A brief discussion of the January floods is included to develop a background for the discussion of the February floods. GEOGRAPHIC SETTING The report describes flooding along streams that drain the Peninsular and Transverse Ranges (fig. 21) in Impe- rial, San Diego, Riverside, Orange, San Bernardino, Los Angeles, Ventura, and Santa Barbara Counties (fig. 1). The Peninsular Ranges include many small ranges that parallel the coastline southeast of Los Angeles. Many CALIFORNIA FLOODS 27 114° 113° 109° 108° I J I 35° |- 28 50 ( ; wet B2 win s RXC . \ Alamo C5), § 34° L- Dam 9&7?" C& § S 9, & T Painted Rock Dam \ 33° |- wwe gils P ~ ~ ~~. ~~. ~~. ~~. *~. » are |- MEey-$Taq Mes "Tes 0 50 MILES TSQ ~ ~ -Air ---- ~~. 0 50 KILOMETERS *~. ~~. EXPLANATION -5.0- Line of equal precipitation-Interval 2.5 and 5 inches A Gaging station used as primary forecast point | | | Mogollon Rim San Carlos Reservoir FIGURE 19. -Isohyetal analysis of total storm precipitation greater than 2.5 inches in central Arizona from approximately 0600 hours m.s.t., February 13, through 2400 hours m.s.t., February 21, 1980. streams draining these mountains are oriented almost perpendicular to the coastline and drain large mountain basins. The Transverse Ranges follow a general east- west line north of Los Angeles. The Santa Ynez Mountains form the westernmost part of the Transverse Ranges. The Santa Monica Mountains, another unit of the Transverse Ranges, start near Point Mugu and extend eastward. Between the Santa Ynez and Santa Monica Mountains is the Oxnard plain, a large coastal lowland that was formed from sediments depos- ited by the Ventura and Santa Clara Rivers. The Los Angeles plain, which is the largest coastal plain in southern California, lies southeast of the Santa Monica Mountains and south of the San Gabriel Mountains, another unit of the Transverse Ranges. This large plain, which encompasses the greater Los Angeles metropoli- tan area, was formed from alluvium deposited by the Los Angeles and San Gabriel Rivers and many small streams that debouch from steep canyons. The entire plain and many of the small canyons are highly urbanized. The major river basins, discussed from south to north, are Tijuana, San Diego, San Dieguito, San Luis Rey, Santa Margarita, Santa Ana, San Gabriel, Los Angeles, Santa Clara, Ventura, Santa Ynez, and Santa Maria. Data are also given for many small basins interspersed among these major basins, and for streams in the Salton Sea basin, especially those tributary to Whitewater River and San Felipe Creek. The headwaters of the latter two streams finger into the Peninsular Ranges between streams that drain to the ocean. Almost all the runoff in southern California originates in the mountains and higher foothills and is directly from 28 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 120° EXPLANATION Areas affected by major flooding - Mid-January storm E] Late January and mid-February storms Mid-January and mid-February storms o 100 MiLES 150 kilometers Cie ta Barbara w Sets gat nnn t a \y Q a.» + + » a & » \ gm.“l... (® San-Diego tolle "" P> Cobrado pul FIGURE 20. -Approximate areas of California affected by major flooding in January and February 1980. rainfall. Because of the steep slopes, the generally FLOODS OF JANUARY 1980 shallow soil mantles, and the very sparse vegetation, runoff is sporadic, with short, rather intense floods The January rainfalls, discussed in an earlier section, followed by long periods of little or no flow. helped the floods of February to develop by wetting the CALIFORNIA FLOODS 29 37° EXPLANATION i: Coast Ranges E San Joaquin Valley Sierra Nevada E Basin Ranges m Transverse Ranges Mojave Desert 36° *| Peninsular Ranges Colorado Desert 35° Purici Urisimg Sil "y Ynez 34° a 10 Z Flo 100 MILES 1 | | I 3g> 100 KILOMETERS 118° - Area of map + C < # ~s, | S8 _ - ® __ ject a e ".g wite n €,, ° ~ «kitiasin reéLake ® # . 5 , $ fiver ® e pi A / fci/Avh % -' @, ~ "9, , ® ® ”44“ 631-173 C e fies-{km e _ e L Henshaw - ® FIGURE 21. -Natural provinces of southern California. (From California Department of Natural Resources, 1954.) soils and causing runoff that partly filled reservoirs. The mid-January storm was statewide, but the most signifi- cant flooding was in the San Joaquin and Sacramento River basins and in coastal basins between Santa Bar- bara and San Francisco. Although flooding was wide- spread in the affected areas, peak discharges at most gaging stations were generally lower than the peak of record. Peak discharges in the basins of the Tuolumne, Mokelumne, Cosumnes, and American Rivers (fig. 20) were among the highest in 20 years. Rainfall totals in southern California had been well below normal prior to the mid-January storm, and soil moisture was low. Consequently, runoff from this storm was low, but the replenishment of soil moisture by the mid-January storm set the stage for flooding from the storms that were to follow in late January and February. The storm of January 28-31 brought large amounts of rainfall to the South Coast Drainage and Southeast Desert Basins climatic divisions (fig. 13), but only light precipitation to other areas of the State. Stations at Cuyamaca Reservoir and Henshaw Dam in San Diego County (fig. 22) reported 3-day totals of 9.23 and 8.14 in, respectively. Lake Arrowhead (fig. 14) reported a 1-day rainfall of 6.26 in on January 28. 30 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 16°45" 116°30° Joins Figure 32 _ -| 33°30 17°15 Vail Lake V-. -~. \. Camp Pendleton ~- gnet Marine Corps @ Base & w S ~ Sas. 4 n - ; N [ \)’\s o Pauma Valley & I os ' . - 33°15 ( 4 Lake Henshaw 5 / / 7. S /m wy AL_® y & ceanside 0 47 o é? Ysabel ooze“ Escondido 0 O Ko 0 < San .$ _ Sutherland o Ca C Reservoir q& a _ p ig x0 - Mo -O Ramona lns 4g? Lake Hodges £232,513? y 00 Ko Creek j A "_| ggo <2- co $000 Boulder C A k- & ra 2\5\| 0 Poway & . O Del Mar San Vincente Py Reservoir ] El Capitan c Reservoir b $o "C yog co & 0 D o 3 akesi escanso g 9 Diego 21} <] \kesnde e 8\ € © Santee ~Los Coches ® 5 Creek O Loveland <2“ 0&9" Reservoir 32°45 "> Morena _ 7. Barrett Reservoir Lake Sweetwater Reservoir xt Creek O “Vb Sunnyside 9 & ek )/0 £ Cre g ower wel- Otay Lake » TATES ..- Otay __ RW $ - Imperial & each ° - City o San Ysidro __ 32°30 117° 116° 1216 a20e _ ise 118° san I, i Lus '- OBISPO -- __ KERN i Sant xll‘ | SANTA ba - _- _- BARBARA |&, \ ~ Los | y 0 5 10 MILES ————— }—'_-1fi.—| RIVERSIDE 0 5 10 KILOMETERS EXPLANATION =m -t- IMPERIAL CITY OF SAN DIEGO 29 [___| PHOTOGRAPH LOCATION-Number indicates figure FIGURE 22. -Major reservoirs and streams in San Diego County, Calif., and in the Tijuana River basin of Mexico. CALIFORNIA FLOODS 31 300 250 |- - 200 |- - 150 |- 100 |- DISCHARGE, IN CUBIC FEET PER SECOND 50 |- 0 3 E 4 [. 1 1 10 20 31 10 20 29 10 _ 20 31 JANUARY FEBRUARY MARCH 1980 FiGuUurRE 23. -Daily discharge for East Twin Creek near Arrowhead Springs, Calif. (station 11058500; site 52, pl. 1), January- March 1980. At most gaging stations in southern California, the peak discharge that resulted from the January storm was much less than those in previous years, but at a few stations the peak became the new peak of record. These stations can be identified in table 23 by the fact that the year given under the heading "Maximum prior to Feb- ruary 1980" is 1980. At 8 or 10 other sites, the January peak was greater than the February peak but was less than the peak of record. None -of the January peaks at these sites was outstanding, and those data are not presented in this report. The peak discharge of 3,710 ft*/s (cubic feet per second) in January at the gaging station on East Twin Creek near Arrowhead Springs (site 52, pl. 1) is the highest since at least 1919. The daily discharge hydro- graph for East Twin Creek near Arrowhead Springs is shown in figure 23. Farther south, in the Tijuana River basin in Baja California, Mexico, the severe rain of January 29-30 produced heavy runoff from the Rio de las Palmas, which flows into Rodriquez Reservoir about 10 mi southeast of Tijuana. The reservoir is formed by a thin-shell, concrete-arch dam completed in 1936; storage began in 1937. The reservoir stores water for irrigation of about 3,000 acres downstream and also for the municipal supply for the city of Tijuana. The large amount of runoff caused concern for the safety of the dam and necessitated large but controlled releases of floodwater. Records of con- tents since 1937 indicate that the reservoir had spilled previously only during March 1938, September 1940, February to May 1941, March 1942, and February and March 1944. Reservoir contents and elevation records supplied by the Ministry of Hydraulic Resources, Government of Mexico, through the International Boundary and Water Commission, United States Section (written commun., 1981) show that on January 29, at 0600 hours, Rodriquez Reservoir was at an elevation of 388.58 ft, its contents was 84,570 acre-ft, and it was not spilling. Twenty-four hours later, on January 30, the reservoir had risen 26 ft to an elevation of 414.69 ft, the contents had increased to 118,000 acre-ft, and there was a maximum spill of 28,600 ft*/s. Releases on January 30 combined with the flood- waters from the Tijuana River to produce an estimated peak discharge of 32,000 ft°/s at Tijuana River near Nestor (site 19), where the previous peak of record was 17,700 ft°/s in 1937. Flooding was widespread along the Tijuana River downstream from the end of the levees (about 2 mi from the international boundary and 0.5 mi upstream from Dairy Mart Road) to the Pacific Ocean (fig. 24). This is a sparsely populated area, and most damage occurred to farmland and livestock. FLOODS OF FEBRUARY 13-21, 1980 As a result of the six storms that struck California during February 13-21, large quantities of rain fell over the western part of the Salton Sea basin and coastal basins south of San Francisco. This series of storms, like that at the end of January, was most severe in southern California and Baja California, but it also produced some flooding to the north in the San Francisco Bay area and in the Salinas River basin. Although the pattern followed by the individual storms of January-February 1980 is not unusual, the number of storms and the short intervals between them are unusual. Soils became saturated, and each succeeding rainfall produced substantial runoff. Few of the storms alone would have caused major flooding; however, the rapid sequence of storms resulted in extreme volumes of runoff and severe flooding. Each of the six storms caused peaks on small streams. Distinct peaks occurred at one or more sites each day from February 14 through February 21, except Febru- ary 17. Each peak was followed by a recession to near base flow. The maximum peaks generally occurred late on February 20 or early on February 21 in the Salton Sea 32 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 24A. -Flooding along the Tijuana River in California on January 30, 1980, near Interstate Highway 5 and Dairy Mart Road looking southwestward at outlet to Pacific Ocean. (Photograph courtesy of San Diego Department of Public Works.) basin and coastal basins in San Diego County, and on February 16 in the Santa Ana River basin and in coastal basins in Ventura and Santa Barbara Counties. Out- standingly high discharges occurred spottily from near Los Angeles to the international boundary. Peaks of record occurred on three streams in the Salton Sea basin and on most streams in the Tijuana River basin. The Los Angeles River carried the highest discharge since at least 1928. The peak of record occurred at a few stations in the basins of the San Dieguito and Santa Margarita Rivers, and of Los Penasquitos and San Diego Creeks, but in most of the study area peak discharges in 1980 were small compared with discharges that occurred in 1862, 1864 (California Department of Water Resources, 1980), 1891, 1916 (McGlashan and Ebert, 1918), 1927, and 1938 (Troxell and others, 1942). Accord- ing to studies by the San Diego County Department of Sanitation and Flood Control (1975), the floods of 1862 and 1916 were the largest ever in San Diego County. In the San Diego River basin, the peak discharges in 1938 also exceeded those of 1980; in the Santa Ana River basin and basins north of Los Angeles, discharges in 1966 (Waananen, 1971) and 1969 (Waananen, 1969, 1975) exceeded those in 1980. Table 5 shows peak discharges for years in which major floods occurred over a large part of the present study area. Other significant floods may have occurred on individual streams or in localized areas, such as the 1966 flood near Los Angeles. Data have not been adjusted for the change in reservoir storage. Many of the southern California dams were built after the 1938 floods. In spite of some large peak discharges, the significance of the 1980 floods in southern California lies CALIFORNIA FLOODS * w 33 wiih FIGURE 24B.-Flooding along the Tijuana River in California on January 30, 1980, at Imperial Beach Naval Air Station looking southward downstream from levees about 3 miles from international boundary. more in the volume and duration of runoff and the large economic losses than in the magnitude of peak dis- charges. Riverine flooding was only one of the problems caused by the storms. High winds and wave action caused heavy damage in several coastal areas, mudflows and slope failures due to saturated soils caused extensive property damage, and broken sewer lines caused contamination of beaches. Seven southern California countiee-San Diego, Riverside, Orange, San Bernardino, Los Ange- les, Ventura, and Santa Barbara-were declared disas- ter areas. VOLUMES OF RUNOFF AND EFFECT ON RESERVOIRS Many streams south of Los Angeles discharged the highest 7- and 15-day volumes of record. Streams to the (Photograph courtesy of San Diego Department of Public Works.) north, although unusually high, discharged volumes sub- stantially less than those previously recorded for 7 and 15 days. Table 6 shows, for selected sites, the highest average discharge for periods of 7 and 15 consecutive days in 1980, their rank compared with other 7- and 15-day averages during the period of record, and the previous highs. The large volumes of runoff had a major impact on the numerous reservoirs in the study area. Most major streams in the report area are regulated at reservoirs used for either municipal supplies, irrigation (conservation reservoirs), or flood control. Although not specifically designed for such, the conservation reser- voirs normally provide a great deal of flood control. Above-average runoff in 1978 and 1979 had significantly increased the contents of the reservoirs. At the end of December 1979, most reservoirs in the southern part of the study area were filled to about 50 to 70 percent of 34 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA capacity. Some reservoirs farther north held more than 85 percent of capacity. The January runoff caused many reservoirs to reach nearly full levels. The runoff from the February storms brought most conservation reservoirs to a full state, and water was spilled from many of them. At most major flood-control reservoirs, the contents did not exceed 60 percent of capacity. The maximum outflow from most reservoirs was less than the peak inflow. Evelyn (1982) credits flood-control reservoirs in the Santa Ana, San Gabriel, and Los Angeles Rivers with having prevented $900 million in damage during the 1980 water year. Recorded and estimated inflow and outflow at selected reservoirs are given in table 7. FLOODS IN MAJOR RIVER BASINS The following sections discuss peak discharge, reser- voir spills, and physical damage in major basins in geographical order, starting at the Salton Sea basin, moving to the Tijuana River basin, and proceeding northwesterly through Santa Barbara County. Sarron SEa Basin The natural drainage area of the Salton Sea is unusual, as about one-fifth of the basin is below or only slightly above sea level. Most major streams originate in the mountains that rim the basin on the western and north- eastern sides. From these mountains, which range from 3,000 to 11,500 ft in altitude, the streams flow in diverse terrain to below sea level and into the Salton Sea. Because the Salton Sea basin is extremely arid, natural runoff is insufficient to maintain streamflow, and most streams are intermittent and experience periods of no flow each year. On most streams in the Salton Sea basin, peak dis- charges in 1980 did not approach the peak of record; however, San Felipe Creek near Julian (site 2, pl. 1), in the western part of the basin, did have a peak discharge almost six times the previous peak of record. The peak discharge at Palm Canyon Creek near Palm Springs (site 11) is almost double the previous peak of record. Flood- water from this normally almost-dry tributary to the Whitewater River ripped out levees, damaged a road crossing, and inundated parts of a golf course in the Palm Springs area. Newspapers reported that on February 18, floodwater from a flood-control channel near Palm Springs destroyed greens and fairways on four well- known golf courses-Tamarisk, Cathedral Canyon, Ran- cho La Palomas, and Ironwood Country Clubs. TuaNa River Basin In the upper Tijuana River basin, large spills from Barrett and Morena Reservoirs (fig. 22) caused dis- charges at Cottonwood Creek above Tecate Creek, near Dulzura (site 16) and at Tijuana River near Dulzura (site 18) to be nearly twice as large as those that occurred in January 1980. The January discharges were much larger than those of 1937 (peak of record for 1986-79). Peak discharges during the February flood have a recurrence interval of about 100 years. Little damage resulted because both streams flow through wide valleys, and because the adjacent flatlands are used primarily for livestock grazing. As in late January, high runoff from the Rio de las Palmas (in the Tijuana River basin in Mexico) into Rodriquez Reservoir caused concern for the safety of Rodriquez Dam, and again large amounts of water were spilled from the reservoir. The daily mean spills on February 20 and 21, 16,400 ft*/s and 16,200 ft*/s, respec- tively, were slightly greater than the daily mean spill of 15,600 ft°/s on January 30. Although the maximum spill from Rodriquez Reservoir on February 21 was only 18,400 ft°/s, it produced an estimated peak discharge downstream on the Tijuana River near Nestor (site 19) of 33,500 ft"/s, slightly larger than the previous record peak that had occurred 3 weeks earlier on January 30, 1980. Flooding was extensive downstream from San Ysidro. The Tijuana River reenters the United States from Mexico near San Ysidro and flows northwestward in an improved, 200-ft-wide channel between earthen levees lined with rock riprap. The unlined channel bottom is composed of sand and is at natural grade, except for a concrete cutoff wall near the downstream end of the levees. The improved channel extends from the interna- tional boundary downstream 2,500 ft. Channel degrada- tion and migration occurred downstream from where floodwaters left the confines of the levees, about 0.5 mi upstream from Dairy Mart Road. Flooding similar to that on January 30 (as shown in fig. 24) occurred. A new river channel formed between the end of the levees and the Pacific Ocean, a distance of about 5 mi. This new channel, located south of the former channel, averaged about 500 ft wide and 4 ft deep. Farmlands were obliterated by channel migration, roads were sev- ered, bridges on Dairy Mart Road and Hollister Street (location of gaging station near Nestor) were left unus- able, and sewer lines were broken. Some of the ocean beaches in the city of Imperial Beach were posted and placed under quarantine for almost 14 months because of pollution. Figure 25 is the hydrograph of daily discharge on the Tijuana River near Nestor at the international boundary. Otay anp SweetwaTER Rivers The 1980 runoff caused the first spill from the present Lower Otay Reservoir, which is formed by Savage Dam on the Otay River. This reservoir was completed in 1919 CALIFORNIA FLOODS 35 30,000 t t T t t t T t u t T-t u u t 25,000 |- 1 20,000 |- 4 15,000 |- 10,000 |- DISCHARGE, IN CUBIC FEET PER SECOND 5,000 |- | § " 1 i i £s i 1 o 1 5 10 15 20 25 31 5 10 15 20 2529 5 10 15 20 25 31 JANUARY FEBRUARY MARCH 1980 FIGURE 25.-Daily mean discharge for Tijuana River near Nestor, Calif. (station 11013500; site 19, pl. 2), January-March 1980. after an earlier dam washed out in 1916. It has a capacity of 56,520 acre-ft and a drainage area of 99.0 mi". The maximum spill from Lower Otay Reservoir, 350 ft*/s, did not occur until March 11. The Sweetwater River heads in the Laguna Mountains of south-central San Diego County and flows southwest- ward to the southern part of San Diego Bay. Two reservoirs, Loveland and Sweetwater, which are located about 20 river miles apart, regulate the discharge. Upstream from Loveland Reservoir, the Sweetwater River and its major tributaries flow in narrow valleys and deep canyons; except for erosion near Descanso, little damage occurred along the Sweetwater River. However, some tributaries east and upstream from Loveland Reservoir had large peak discharges that destroyed small bridges and grade-level crossings, thus isolating ranches. Downstream from Loveland Reser- voir, roads and golf courses were damaged. Discharges in the lower 8 mi of the Sweetwater River are controlled by Sweetwater Dam, which was completed in 1888. The left side of the dam has always had a spillway; water has spilled on several prior occasions. The right end of the dam washed out in 1916 and was replaced by an overflow siphon system that was completed in 1921. During the February 1980 storms, water flowed through the siphons for the first time. Downstream from the reservoir, floodflows destroyed two grade-level crossings near Sunnyside. San DirEco River Basin The San Diego River heads between the northern edge of the Laguna Mountains and the southern edge of the Volcan Mountains in central San Diego County and flows southwestward into El Capitan Reservoir. That reser- voir, which has a capacity of 112,000 acre-ft and a drainage area of 188 mi", spilled for the first time since 1941. Boulder Creek, the major tributary from the east, joins the San Diego River 2 mi upstream from El Capitan Reservoir. The flow of Boulder Creek is regulated by Cuyamaca Reservoir, which is formed by an earthfill dam completed in 1887. The reservoir has a capacity of 12,150 acre-ft and a drainage area of 12 mi". Cuyamaca Reservoir spilled from February 23 to April 8, 1980 (M. Brown, Helix Water District, oral commun., 1982). The 1980 spill from San Vicente Reservoir on San Vicente Creek is the largest since the dam was finished in 1943. Crossings at Vigilante Road (immediately downstream) and Moreno Avenue (near the mouth of San Vicente Creek) were washed out; the floodflows inundated homes and stranded many residents. Figure 26 shows flooding in Moreno Valley. San Vicente Creek enters the San Diego River from the north near Lakeside, about 8 mi downstream from El Capitan Reservoir. Many small tributaries to the San Diego River have a major part of their drainage basin in residential communities of the San Diego metropolitan area. Figure 27 shows flooding along Los Coches Creek, which enters the San Diego River from the south at Lakeside and is typical of these streams. In some reaches of the San Diego River, channel scour was extreme. The flood tore out a 20-ft-diameter steel culvert at Channel Road crossing near Lakeside and deepened the channel by 10 to 20 ft at Riverford Road. The San Diego River caused havoc in San Diego, especially in Mission Valley between Interstate High- ways 5 and 15. From State Highway 163 to Interstate Highway 5, commercial development has encroached on the several-hundred-foot-wide valley floor and narrowed the river channel to approximately 50 ft. Water reported to be 7 ft deep in places closed most secondary streets. Businesses, shopping centers, hotels, and golf courses were damaged (fig. 28). Thousands of individuals were evacuated. Pryde (1982) estimated a peak discharge at Mission Valley of 27,000 ft*/s, which is much larger than the discharge of 3,420 ft*/s 5 mi upstream at the gaging station near Santee (site 21). The rapid increase in discharge is attributed to the highly urbanized drainage area downstream from the station. The rapid increase occurred even though (1) the drainage area at the gaging station is nearly 90 percent of the area at Mission Valley, (2) the river flows through many small ponds enroute from the gaging station, and (3) only three tributaries of any significant size-Alvarado Canyon Creek from the 36 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 26. -Moreno Valley, Calif., looking northward up San Vicente Creek downstream from San Vicente Reservoir, February 21, 1980. (Photograph courtesy of San Diego Department of Public Works.) east and Murphy Canyon and Murray Canyon Creeks from the north-enter the river between the gaging station and the downstream end of Mission Valley. The peak discharge at the gaging station, 3,420 ft"/s, has a recurrence interval of approximately 9 years and is far less than the peak of 70,200 ft°/s in 1916. The peak discharge in Mission Valley in 1916 was 75,000 ft*/s. After major floodflows had passed, the water level of El Capitan Reservoir was lowered about 30 ft for safety in case of a damaging earthquake. The water released in CALIFORNIA FLOODS 37 FIGURE 27. -Lakeside, Calif., looking westward, February 21, 1980. Los Coches Creek flows from lower left and joins San Diego River in upper right. (Photograph courtesy of San Diego Department of Public Works.) this safety effort and wasted to the ocean was valued at more than $4 million (San Diego County Flood Control District, 1980). San DiEcurro River Basin Santa Ysabel Creek joins Santa Maria Creek to form the San Dieguito River, which enters Lake Hodges south of Escondido. Peaks of record occurred at Santa Maria Creek near Ramona (site 29) and at Guejito Creek near San Pasqual (site 28). Guejito Creek is tributary to Santa Ysabel Creek. Santa Maria Creek is one of the few streams that had a higher discharge in 1980 than in 1916. At Santa Ysabel Creek near Ramona (site 27), the 1980 discharge was slightly more than one-third of the 1916 discharge. Sutherland Reservoir, located on the headwaters of Santa Ysabel Creek, spilled for the first time since it was completed in 1954 and contributed to an estimated spill of 22,000 ft*/s at Hodges Dam (Lake Hodges); this was the largest spill since 1927, when an estimated 47,500 ft*/s was spilled. Downstream from Hodges Dam, the San Dieguito River damaged two bridges near the mouth and inundated the Del Mar horse track and fairground (fig. 29) to a depth of 3 to 5 ft. Residents of the area and many valuable horses were evacuated. San Luis Rey River Basin The San Luis Rey River heads in the mountain area of north-central San Diego County and flows southwest- ward into Lake Henshaw above Henshaw Dam. Because 38 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 28. -San Diego River in lower Mission Valley, San Diego, Calif., looking westward, February 21, 1980. (Photograph courtesy of San Diego Department of Public Works.) the reservoir has a large capacity relative to its drainage area of 205 mi", it contained all inflow during the flood period and was the only reservoir in San Diego County that did not spill during the February 1980 floods. The dam is near Elsinore fault, and because of the possibility of earthquake damage to the dam, the State Division of Safety of Dams has ordered that large volumes of water not be stored over prolonged periods. A controlled release that followed the flood was kept small enough to avoid damage downstream from the dam. Some damage was caused downstream from the dam by tributary inflow during the flood period. The bridge at West Lilac Road near Pauma Valley and the grade-level crossing at Couser Canyon Road near Pala were washed out, and the new Interstate Highway 15 bridge near Pala was damaged. Near Oceanside, the Douglas Road bridge, the crossing at St. Francis Priory, and the Lorretta Road crossing just downstream from the gage (site 35) suffered flood damage. A large industrial-park complex, about 2 mi upstream from Interstate Highway 5 and 0.8 mi north of the San Luis Rey Mission, was inundated (fig. 30) on February 21 when a break occurred in the 3,000-ft levee along the San Luis Rey River. At most gaging stations in the San Luis Rey River basin, peak discharges were probably the highest in the last 50 to 65 years. On the San Luis Rey River itself, the peak was small compared with those in 1891 and 1916. For example, at Oceanside (site 35) the 1980 peak discharge was 25,000 ft*/s. A discharge of 95,600 ft/s occurred at Oceanside in 1916. Young and Cruff (1967, p. 60) show that a discharge of 128,000 ft*/s occurred in 1891 at a site a few miles upstream. CALIFORNIA FLOODS 39 Md Atchison, Topeka a" 4 Santa Fe R? FIGURE 29. -Racetrack and fairgrounds at Del Mar, Calif., looking eastward up the San Dieguito River, February 21, 1980. (Photograph courtesy of San Diego Department of Public Works.) Santa Marcarita River Basin Vail Lake, which is on Temecula Creek about 10 mi east of Temecula in Riverside County, spilled sometime between 0400 and 0900 hours on February 21, 1980, for the first time since the dam was completed in November 1948. Vail Lake has a drainage area of 320 mi", and the capacity of the reservoir at the spillway level is 49,370 acre-ft at an elevation of 1,470 ft. Data supplied by the Rancho California Water District (J. Schelege, written commun., 1981) indicate that the lake elevation was 1,466.8 ft when observed between 1400 and 1500 hours on February 20, 1980, and that the maximum elevation reached during spill was 1,473.00 ft. Contents at the time of maximum spill was approximately 52,000 acre-ft, and the maximum spill was estimated to be 8,000 ft*/s. Peak discharges at gaging stations in the Santa Mar- garita River basin also were generally the highest in the last 50 years, approaching the magnitudes of discharges during the 1927 floods. Murrieta Creek, which along with Temecula Creek forms the Santa Margarita River, expe- rienced a peak flow of 21,800 ft*/s at the gage at Temecula (site 37), the highest since records of peak discharges began in 1930. The daily discharge hydro- graph for this station is shown in figure 31. On the Camp Joseph H. Pendleton Marine Corps Base, the Santa Margarita River eroded reaches of the left bank below Basilone Road and destroyed sections of a railroad spur. Sections of this railroad were also destroyed during the 1978 floods. 40 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA € FIGURE 30. - Industrial-park complex near Oceanside, Calif., flooded by San Luis Rey River, looking northeastward from bluff behind San Luis Rey Mission, February 21, 1980. (Photograph courtesy of U.S. Army Corps of Engineers.) Santa Ana River Basin The Santa Ana River is the largest coastal stream in southern California and has a drainage area of about 2,470 mi" at its mouth (fig. 32). The main stem and two of the major tributaries, Mill and Bear Creeks, originate in the San Bernardino Mountains (fig. 21). The river flows westward and debouches from a canyon onto an alluvial flood plain a few miles east of San Bernardino. Several other tributaries also originate on the western slope of the San Bernardino Mountains, flow southward, and enter the main river system. Lytle Creek, another major tributary, has its source in the San Gabriel Mountains (fig. 21) and flows southeastward to join the main stem near San Bernardino. Downstream from Lytle Creek, the river flows southwestward into Prado Reservoir, which is 31 mi upstream from the mouth. Below Prado Dam the river enters Santa Ana Canyon, which lies between the Chino Hills and the Santa Ana Mountains; those highlands physically separate the inland valleys of the upper basin from the coastal plain. Farther down- stream, the river flows through large metropolitan areas and into the Pacific Ocean. The flood of January 22, 1862, the largest in the history of the Santa Ana River basin, destroyed the former settlement of Agua Mansa (southwest of Colton), which had been 9.2 mi upstream from the gaging station of Riverside Narrows near Arlington (site 62). Computa- tions based on old flood marks indicate a peak discharge of 320,000 ft"/s. Discharges at the gaging station were 100,000 on March 2, 1938, and 19,500 ft/s on February 18, 1980. The 1980 peak discharges in the Santa Ana River basin above Prado Dam were low compared with past floods. For example, the peak discharge of 5,930 ft*/s at Santa Ana River near Mentone (site 46) was much less than the 1891 peak of 53,700 ft"/s and the 1938 peak of 52,300 ft"/s. Runoff volumes, however, were among the highest of this century. The contents of the Prado Flood Control Reservoir on the Santa Ana River reached about 111,000 acre-ft on February 22, the second highest of record (fig. 33). The highest contents of record, 130,000 acre-ft, occurred on February 25, 1969. Figure 34 shows contents as a function of time for January through April 1980. Unusu- CALIFORNIA FLOODS 41 8,000 T T T T T T T T T T T T T 6,000 |- - 4,000 |- DISCHARGE, IN CUBIC FEET PER SECOND 2,000 k - o y py , u b 20 25 31 5 10 15 20 25 31 5 10 15 20 25 29 DECEMBER JANUARY FEBRUARY 1979 1980 FIGURE 31. -Daily discharge for Murrieta Creek at Temecula, Calif. (station 11043000; site 37, pl. 1), December 1979-February 1980. ally large releases from Prado Dam continued until mid-May. Mudflows and slope failures due to saturated soils caused extensive property damage throughout the Santa Ana River basin. The Harrison Canyon debris basin at 40th Street and Harrison Street in San Bernardino was filled by mudflows after the storms of January 9, 14, and 28, February 16, and March 10 (K. Mashburn, San Bernardino County Flood Control District, oral com- mun., 1981). Levees were overtopped but did not fail. This 0.6-mi" drainage basin, which is tributary to East Twin Creek (see fig. 32), virtually had been made a big sand box by a fierce fire in September 1979 that burned most of the basin. The fire destroyed the root systems of vegetation and left a loose mantle. Attempts to seed the barren hillsides before the winter storm period had been unsuccessful. Large mudflows moved downstream at high velocities, and it was not uncommon for the Harri- son Canyon debris basin to fill and spill within 20 minutes during these storms. Hampshire Avenue, immediately below the basin, was designed as an inverted "V" to carry floodwater, but it could not accommodate the large mudflows and debris flows. The mud reached depths of 6 to 7 ft on Hampshire Avenue, and more than 60 homes downstream from the debris basin were destroyed by the water and mudflows (fig. 35). San Jacinto River and Lake Elsinore. -The San Jacinto River flows northwestward from its headwaters in the San Jacinto Mountains in Riverside County, passes near the town of San Jacinto into San Jacinto Valley, and turns southwestward toward Lake Elsinore, which is 30 mi downstream from San Jacinto (see fig. 32). Many years ago the course of the river was altered and the reach past San Jacinto and through the valley was leveed. Downstream from Bautista Creek, a leveed bypass channel was constructed to the east and north of the town. On the morning of February 21, 1980, the levee southeast of (upstream from) San Jacinto failed, and the floodwater reverted to the original river channel through the center of town. Figure 36 shows the destruction to the levees and the damage sustained from the floodwater in San Jacinto. Other levees to the north also failed, thus allowing floodwater to spread out across valley farm- lands and into town. Detailed analyses of the failures are presented by Edwards (1982) and Sciandrone and others (1982). One of the major disasters during the 1980 flood occurred at Lake Elsinore, the terminus of San Jacinto River. Historically, the lake was dry for many years in succession, but since 1965, when importation of Colorado River water began, a lake of about 6 mi" has been maintained. During wet periods the shallow lake expands. Prior to 1980, outflow is known to have occurred only in 1872, 1883-84, and 1916-17; there probably was outflow in 1862. During the rare occur- rences of outflow, the direction of flow is northeastward to Temescal Wash (also called Temescal Creek). Large amounts of urbanization developed around the shores of the lake during the years of low lake levels. More history of the lake is published in Water-Supply Papers 441 and 961 (U.S. Geological Survey, 1918, 1943). The Riverside County Parks and Recreation Depart- ment recorded a lake-surface elevation of 1,246.59 ft on February 13, 1980 (contents, 61,200 acre-ft). At that time, the lake was about 13 ft below the natural outlet and 20 ft below the tops of gravel piles that had been deposited in Temescal Wash by tributary inflow, mainly from Wasson Canyon, during the many years when there had been no outflow from the lake. During the major part of the flood, the lake surface rose several inches a day. By February 23, the surface had risen to 1,259 ft (contents, 124,000 acre-ft). At this time the Corps of Engineers let a contract for clearing the Temescal Wash channel to an elevation of 1,260 ft (White, 1982). Dredg- ing progressed around the clock as the lake continued to rise. The dredging prevented about 1.5 to 2 ft of rise in the lake (White, 1982). Simultaneously with the dredg- ing, homes and other developments were being pro- tected with sandbags and levees, and residents were being evacuated. FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 42 'pge; '{juno; saroduy so7 ut utseq Joigen ueg ay} ut pue 'sopuno; pue 'outprewog wey ut sureans pue dofepy- Z8 ainBy sereoiput HdWH9OLOHd [___] 98 NOLLWNY14X3 SH313W070D4 OL S 0 r-- SITA 0L S 0 zZ ainbig surop z30 ouegstde; uenp ueg olLll s6LL e0CL dm I I poumpy 40 yodmap 2497 buysesg aipusgq a esap| 2150 Mwet _.. ) | or 'ss z use W O a uojbugunp o 11004asay “we aw % uofiup 'b * AVG a « A E> 4 pooujtoy $6$ 00é euy ejues 0 [~7] ip yoerag O |- Ying ko a P1 0 anoug 0 MW 5 & oofio b F, abuein 0 /A cmcom wu, ag [_\] 0 cqurep ueg «mofl 3&4 3 ; JavAu & e5 o ® 0 wrayrew ($ ""@, yo ey ® Y Toy § 2497 o 37 {anld % [~] ss 110n4asay weg opeiq QVV juowuneag OopP4d 43 0 0 0 72 < 0, 4 & "ay apisianiy 0 0 (6) € s o |- ofiw 3 3 S 5 § - oueju smouep auojua $52va yoyo) "_o C 2 o woulsd 1enuum WWpo s A40 puepdp /$ yieq umpjeg 0 Ton ¢ @ oue o - opuop up' Fess j o o "C: ory oumprewag & $* 4,26 & |§ ues m @ o |3 wa 3 s* /S O F 5 @) -. s aw A ove p A 6 410on4asay 12° w SC & Jougoo ung $ 4 (@] 0 /g 1 S 0 o bi x A 63 # 2907 nag big kayo & ~ ayD -| |_ 2407 __| n olll SlolLL Cb. 711 - StoEE 0 sr & Tp ainbig SlotE oll CALIFORNIA FLOODS 48 FIGURE 33. -Prado Dam and Flood Control Reservoir, Calif., looking northward from Santa Ana Canyon, February 1980, just after maximum storage had been obtained in the reservoir. (Photograph courtesy of San Bernardino County Flood Control District.) Inflow reached a maximum of slightly more than 8,000 on February 22, and then decreased steadily, except for a slight increase in early March, to less than 100 ft*/s in mid-April. Outflow started on March 7 and reached a maximum rate of almost 240 ft/s later in the month. The surface of Lake Elsinore reached a maximum elevation of 1,265.72 ft on March 20 (contents, 164,000 acre-ft), and the surface area was about 10 mi". Data from Riverside County indicate that inflow during the period when the lake was rising was about 103,000 acre-ft. Another 5,800 acre-ft flowed into the lake after the maximum lake level had been reached. The daily discharge hydrograph for the San Jacinto River near Elsinore (site 66), where inflow to Lake Elsinore is measured, is shown in figure 37. Figure 38 shows the changes in contents and stage of the lake from February 1 to September 30, 1980. Flooding from Lake Elsinore damaged many homes and facilities in low-lying areas around the lake. The environmental assessment prepared by the Federal Emergency Management Agency (V. Thompson, written commun. , 1981) lists 874 buildings and dwellings affected by the floodwater. Approximately 300 structures were 44 120 T T T T T T T T T T T - o ls] T 80 |- 60 |- 40 |- CONTENTS, IN THOUSANDS OF ACRE-FEET 20 |- JANUARY FEBRUARY MARCH APRIL 1980 FIGURE 34.-Contents of Prado Flood Control Reservoir, Calif. January-April 1980. W ze w 1 10 _ 20 31 10 20 29 10 20 31 10 20 30 U FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA damaged by the rising lake (figs. 39, 40). In addition, about 100 septic tanks serving undamaged structures were flooded and became unusable. Nearly all the approximately 400 mobile homes and travel trailers in the threatened area were relocated in time to prevent damage. An estimated 2,000 residents were displaced. Skylark Airport, at the southeastern end of the lake, and State and city parks and other recreational facilities were inundated. Santa Ana River downstream from Prado Dam. -On the Santa Ana River below Prado Dam, the highest discharge since regulation began in 1941 occurred on February 21. Extensive damage occurred in Santa Ana between 17th Street and Harbor Boulevard. Daily mean discharges of more than 4,400 ft°/s were recorded at Santa Ana (site 76) from February 17 to February 26, 1980, and daily mean discharges of 2,300 ft*/s or larger occurred during the period March 2-16, 1980. Generally, a daily mean discharge of 2,300 ft*/s is exceeded only one-half of 1 (0.5) percent of the time. The continuous high discharges scoured the riverbed to depths of up to 20 ft and undercut segments of the concrete lining along *s ai FIGURE 35A. -Flooded homes along Hampshire Avenue below Harrison Canyon debris basin in San Bernardino, Calif., February 1980, showing debris basin with Hampshire Avenue in the foreground. (Photograph courtesy of San Bernardino County Flood Control District.) CALIFORNIA FLOODS 45 the banks, thus causing it to break off. Repairs to the concrete linings and construction of grouted rock stabi- lizers are estimated to have cost the U.S. Army Corps of Engineers and local agencies about $4.5 million (R. Douglas, U.S. Army Corps of Engineers, oral commun., 1981). Scour was severe at six major bridges and numerous minor bridges. The Fifth Street bridge was closed to traffic for almost a year. Part of the reason for the long closure was concern that a combination of heavy traffic and an earthquake, which might occur while the bridge was in a weakened condition, could collapse the bridge and result in loss of life. Keeping traffic off the bridge eliminated that possibility. Piers of this bridge are supported on piling, the tops of which were 1 to 2 ft below the streambed prior to the flood. After the flood, 10 to 15 ft of piling was exposed. Nelson (1982) states that up to 18 ft of scour occurred. The photograph in figure 41A, taken from the left downstream bank, shows the site on an unknown date prior to the February 1980 storm. The photograph in figure 41B was taken on March 3, 1980, from the right bank on the upstream side of the bridge at a discharge of about 5,000 ft*/s. The photograph in figure 41C, taken from the left downstream bank after the high-water period, shows the amount of scour. San GABRIEL anp Los Anceues River Basins The San Gabriel River (fig. 32) heads in the San Gabriel Mountains north of Los Angeles and flows south- ward to the Pacific Ocean near Seal Beach. The many tributaries to the Los Angeles River head in the western part of the San Gabriel Mountains and flow south to the river (fig. 42). Part of the upper drainage is from the San Fernando Valley; the river flows eastward through the valley, then flows south through the coastal plain and enters the ocean near Long Beach (fig. 32). The San Gabriel River is regulated by several reser- voirs. The most downstream one is formed by Whittier Narrows Dam. The reservoir is fed by the San Gabriel River, Mission Creek, and Rio Hondo. Most of the inflow is from the San Gabriel River; most of the outflow is released to Rio Hondo, a tributary to the lower part of the Los Angeles River. FiGURE 35B. -Flooded homes along Hampshire Avenue below Harrison Canyon debris basin in San Bernardino, Calif., February 1980, showing extent of sediment deposits. (Photograph courtesy of San Bernardino County Flood Control District.) 46 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 36A. -Flood damage in San Jacinto, Calif., February 1980: Aerial view looking northwestward just downstream from levee break on San Jacinto River, near trailer court at Mountain Avenue and Old Mountain Avenue, February 21, 1980. (Photograph courtesy of Riverside County Flood Control and Water Conservation District.) Flood-control reservoirs in the San Gabriel River The Los Angeles River is regulated by Sepulveda Dam basin greatly reduced the peak discharge of the river and | (see fig. 42). Many tributaries that head in the mountains caused the discharge below Santa Fe Reservoir (site 77) | and join the river below the dam are also regulated by during 1980 to be much less than the previous peak of | reservoirs. The peak discharge at the Los Angeles River record, which occurred in 1969. The discharge of the 1969 | at Sepulveda Dam (site 82) was the highest since 1929, peak is 30,900 ft°/s; that of the 1980 peak is 18,500 ft*/s. | but it was only sightly larger than the former peak of Downstream from Santa Fe Dam (fig. 43), floodflows | record in 1978. By contrast, the February 16 peak were contained within the flood-control channel. discharge at Long Beach (site 87) of 129,000 ft"/s is 26 CALIFORNIA FLOODS 47 FIGURE 36B.-Flood damage in San Jacinto, Calif., February 1980: Aerial view looking northwestward near State Street and Ramona Boulevard, February 21, 1980. (Photograph courtesy of Riverside County Flood Control and Water Conservation District.) percent greater than the previous high since recordkeep- ing began in 1928. The previous peak of record occurred in 1969. Coastar Basins NortH anp West or Los AnceLEs Flood damage was extensive in the small basins between the Los Angeles and Santa Clara Rivers. Homes were damaged by mudflows and floodwaters, and newspaper accounts of these events were daily occur- rences. The Laurel Canyon area of Los Angeles sus- tained flood and mud damage to vehicles and homes, and a woman reportedly was hospitalized after her house slid off the foundation and into the street. In some areas, such as Mount Wilson, mud flowed easily and rapidly from slopes that had been denuded by brush fires of the previous summer. Wells (1982) and Davis (1982) detail amounts of movement and describe the impact of brush 48 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 36C. -Flood damage in San Jacinto, Calif., February 1980: Residential area near intersection of Camino Los Banos and First Street, February 21, 1980, shortly after levee break on San Jacinto River. (Los Angeles Times photograph.) fires on the floods. Slosson and Krohn (1982) and Weber (1982) attribute well-administered building codes and improved methods of tract development with having prevented much additional damage. Flooding and debris reportedly closed the Hollywood Freeway in downtown Los Angeles during morning rush hours of February 15; landslides closed four of the five westbound lanes of the Ventura Freeway near Los Angeles the same day. Mudslides closed the Pacific Coast Highway in Malibu, and Highway 101 was closed at many locations between Goleta (about 5 mi west of Santa Barbara) and the San Fernando Valley because of flood- ing on February 16. The Topanga Canyon area in the Santa Monica Mountains suffered awesome destruction (fig. 44) when the usually dry creek flooded after a week of rain. Flooding, mudslides, and debris flows caused suffi- cient damage in Ventura and Santa Barbara Counties to cause those counties to be eligible for disaster aid. However, peak discharges on the major streams were not unusual. Much higher discharges have occurred several times (table 5) on the Santa Clara, Ventura, Santa Ynez, and Santa Maria Rivers. Records for most small streams are too short to provide a true comparison of the 1980 flood with earlier floods; however, many of the records show higher floods in 1969 and 1978 than in 1980. Such was not the case in Calleguas Creek basin- where Arroyo Simi and Conejo and Calleguas Creeks each had a higher discharge in 1980 than in 1969 or 1978. Taylor (1982) attributes the high discharge in Calleguas Creek to the fact that Arroyo Simi and Conejo Creek, the two major tributaries to Calleguas Creek, peaked almost simultaneously. She stated that concentration time on Arroyo Simi has decreased considerably in the last 46 years. Parts of the Point Mugu, U.S. Naval Air Station, Pacific Missile Test Center, located about 50 mi west of Los Angeles on the coast, were flooded on February 17 when a dike along Calleguas Creek failed (fig. 45). About 60 percent of the low areas of the base reportedly were under 2 to 5 ft of water, causing about 3,000 residents of the housing area to be evacuated. There was no damage to the sophisticated missile-launching facilities. Taylor (1982) presents a chronology and analysis of the failure. Floods in the Ventura River basin carried extreme amounts of sediment off 13 basins that had been denuded of vegetation by fires in 1979 (Taylor, 1982). Much more severe flooding probably would have occurred had flood- fighting equipment and personnel not been mobilized quickly because of information obtained from recently CALIFORNIA FLOODS 49 FIGURE 36D. -Flood damage in San Jacinto, Calif., February 1980: Looking east toward Mountain Mobile Park and residential area from San Jacinto High School on Idyllwild Drive, just north of Tiger Lane, February 23, 1980. (Photograph courtesy of U.S. Army Corps of Engineers.) installed flood-warning systems in the Sespe Creek and Santa Ynez River basins (Bartfield and Taylor, 1982; Stubchaer, 1982). EFFECT OF FLOODS ON GROUND-WATER LEVELS In southern California, sustained high streamflow con- stitutes an important source of recharge to the ground- water basins. Because of precipitation during the winter, followed by pumping during the summer, ground-water levels tend to show large seasonal fluctuation, rising in winter and early spring and falling in summer and autumn. In addition to this seasonal cycle, recharge varies greatly from year to year as a result of large variation in annual precipitation. Figure 46 shows changes in the water level at an index well in Baldwin Park, about 15 mi east of central Los Angeles, from January 1977 to December 1980. This well is about 1.5 mi east of the San Gabriel River and 1 mi south of the Santa Fe Dam Flood Control Basin. The water level in this key observation well rose 33.7 ft between January and June 1980. Wells in many coastal basins indicated similar water-level changes as a result of recharge from the February 1980 flood. 8,000 T-T-t-t-t-t-t-t-t-t-tt-t-t-t-t-t-t -+- 6,000 |- 4,000 |- 2,000 |- 0 IIllImlllllll £000 1 5 10 15 20 25 31 5 10 15 20 2529 5 10 15 20 25 31 5 10 15 JANUARY FEBRUARY MARCH APRIL 1980 DISCHARGE, IN CUBIC FEET PER SECOND FiGurE 37.-Daily discharge for San Jacinto River near Elsinore, Calif. (station 11070500; site 66, pl. 2), January-April 1980. COASTAL DAMAGE The southern California coastline was hit hard by high winds and waves that damaged homes, marine facilities, 50 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 180 -T -T -T- TO 160 [- 140 |- 120 |- 100 |- 80 [- CONTENTS, IN THOUSANDS OF ACRE-FEET 60 C 1 5 10 15 20 25 30 SEPTEMBER 1 5 10 15 20 2529 5 10 15 20 25 31 FEBRUARY MARCH 1980 1,270 [ 1,265 |- T 1,260 1,255 STAGE, IN FEET 1,250 |- 1,245 ~ 1 5 10 15 20 25 30 SEPTEMBER 1 5 10 15 20 25 29 5 10 15 20 25 31 FEBRUARY MARCH 1980 FIGURE 38. -Contents and stage of Lake Elsinore, Calif., February, March, September 1980. and beaches. At Oceanside, several homes and small motels were almost destroyed by surf and wave action (fig. 47). The beach was reduced to a cobble pavement. At Santa Barbara, waves removed up to 2 ft of beach material from Leadbetter Beach (Shaw, 1982). Coastal residents northwest of Los Angeles suffered from heavy surf that ran as much as 8 to 9 ft above normal and threatened to erode their homes from the front, while flooding and mudslides from the rear threatened to push homes into the ocean. A sewer line running into the Tapia Sewage- Treatment Plant in Agoura (fig. 42) was broken on February 16 when the plant was flooded, and raw sewage flowed down Malibu Creek and into the ocean. Approximately 65 mi of ocean beaches in Los Angeles County, extending from the Ventura County line to Los Angeles harbor, were closed to swimmers and surfers for more than 3 weeks because of a potential health hazard. Beaches in the city of Imperial Beach, San Diego County (fig. 22), were quarantined for almost 14 months because of sewage carried to the ocean by the Tijuana River. Beaches at San Diego were closed for about 2 months. The harbor patrol reported that many of the 6,000 boats moored at Marina Del Rey, in Los Angeles, had internal flooding and required pumping, and boats at numerous other marinas were damaged. MONETARY DAMAGE AND FLOOD RELIEF The large volumes and long durations of flow were as instrumental in causing high economic damage in south- ern California as were peak discharges. The February floods were more costly than any others that have occurred. The floods caused much damage because mas- sive urban areas have developed since the last major flood. As stated earlier, San Diego, Riverside, Orange, San Bernardino, Los Angeles, Ventura, and Santa Bar- bara Counties were declared disaster areas. Eighteen lives were lost in these counties as a result of the January and February storms and floods. Once the counties had been designated disaster areas, the Federal Emergency Management Agency (FEMA) designated the disaster declaration FEMA-615-DR-CA on February 21, 1980 (C. Smith, oral commun., 1981). This act enabled cities and other governmental agencies, as well as nonprofit institutions that have State and local jurisdiction, to file damage applications with FEMA for monetary support. Damage applications were received from 335 public entities for financial assistance totaling about $113 million; more than $60 million was obligated for this disaster through August 1981. The following table gives a breakdown of the project applications by type, as designated by FEMA (D. Taiclet, written commun., 1981), and the monies requested: Amount, Class in million dollars A. Debris clearance '43.9 B. Protective measures ......................... 10.7 C. Road SysStem$ ............2.................... 24.8 D. Water-control facilities ...................... 14.4 E. Public buildings and equipment............. A F. Public utilities systems ...................... 13.9 G. Facilities under construction ................ T H. Private, nonprofit organizations ............ .2 I. rere rere errr ere.}. 3.3 X. Miscellaneous................................. 4.4 "Includes six applications totaling $1.4 million from agencies in Santa Cruz County (not covered in this report). In addition, almost $6.6 million has been specified for the following FEMA programs: (1) individual family CALIFORNIA FLOODS FIGURE 39A. -Lake Elsinore, Calif., looking eastward, cirea 1950. FIGURE 39B.-Lake Elsinore, Calif., looking eastward, February 1980. 51 52 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 40. -Residential area along Lake Elsinore, Calif., February 1980. (Photograph courtesy of U.S. Army Corps of Engineers.) grants to meet immediate needs ($4,275,000); (2) tempo- rary housing (rental costs) ($551,500); and (3) mission assignment letters, which is FEMA's means of request- ing other agencies to do work in connection with this disaster ($1,801,000). The first program is limited to $5,000 per family; 75 percent of the funds come from FEMA, and 25 percent come from the State. The second program is limited to rent for 1 year. Damage estimates and costs associated with flood- related emergency activities have been compiled and published by the U.S. Army Corps of Engineers (1981b). That report states that flood, mudslide, and beachfront- erosion damage totaled about $500 million in southern California; according to the report, about $17 million was spent for emergency operations, repair, and restoration. In Riverside County, which experienced its most costly flood period on record, the report attributes 10 deaths and property damage of more than $70 million to the floods. In addition, about $4 million was spent for flood fighting and other emergency operations, and about $6 million for rehabilitation projects following the flood. This was the largest single expenditure of funds for flood fighting and rehabilitation in any southern California county during the 1980 floods. The Corps' report further emphasizes the San Jacinto levee break as having the most serious consequence of all the effects of the 1980 floods in southern California. Many people were left homeless, residences were dam- aged and mobile homes destroyed, and many roads and streets were seriously damaged as a result of flooding. Damage was estimated at $29 million in urban areas and $1.5 million in agricultural areas. SEDIMENT TRANSPORT On several streams during the 1980 flood, channel scour, bank erosion, levee failure, channel migration, mudslides, debris-basin spills, and road overflow resulted in the transport of great quantities of sediment. Sediment transport during periods of high flow is espe- cially important because at these times the river chan- nels will try to obtain a state of equilibrium, either by aggradation or by degradation, to compensate for the ARIZONA FLOODS 58 many changes to the basin that have been induced, mainly by man. Streams that have gravel operations in the river bed, have infiltration ponds in the river chan- nel, or have artificial controls or drop structures usually undergo drastic changes from sediment movement dur- ing floods. During high-flow periods, streams also carry great quantities of sediment to the sea and replenish the beaches. However, the large number of reservoirs that have been established during the past century serve as sediment traps, reducing the rate of replenishment. As a result, many beach areas have been replenished by man at considerable expense. Sediment movement also causes problems because of channel deposition. Table 8 summarizes sediment data for the Santa Ana, Santa Clara, and Ventura Rivers (sites 76, 99, and 106) for storm periods of 25 days during the 1969 water year, 28 days during the 1978 water year, and 33 days during the 1980 water year. The percentages of annual load transported during the storm periods range from 64.3 to 76.2 for the Santa Ana River, 95.9 to 98.2 for the Santa Clara River, and 98.9 to 99.7 for the Ventura River. The lower percentages for the Santa Ana River may have resulted in part from the presence of Prado Reser- voir, which permits substantial regulation of the flow in the lower reaches of the Santa Ana River and acts as a sediment trap for upper basin flow. Also, when large quantities of water are released from the reservoir for prolonged periods of time, the released water transports large sediment loads obtained from the reservoir and from the stream channel. Large percentages of the total annual sediment load are transported during postflood releases. For example, the amount of sediment trans- ported during the postflood period in 1980 is 19 percent of the yearly total and 25 percent of what was transported during the four storm periods during the 1980 water year. Table 9 shows annual sediment loads for water years 1969-80 and compares the movement during storm periods of 1969, 1978, and 1980 with the 12-year totals. The load of sediment transported, during 86 days, ranges from 66 to 94 percent of the 12-year total. Figure 48 relates the rate of sediment discharge to the combined water and sediment discharge rate at the Santa Clara River at Montalvo (site 99). ARIZONA FLOODS Although precipitation occurred throughout most of Arizona during the storms of February 13-22, 1980, large amounts of runoff occurred only in the mountains of central Arizona (fig. 1). Minor floods occurred in local areas within the Little Colorado River, Havasu Creek, and Bill Williams River basins. Moderate to severe floods occurred on unregulated streams in the basins of the Salt, Agua Fria, and Hassayampa Rivers, which are tributaries of the Gila River (pl. 2). The most severe floods occurred on the Salt and Agua Fria Rivers down- stream from water-conservation reservoirs. Maricopa, Yavapai, and Gila Counties were declared disaster areas. The peak discharge of 170,000 ft/s on the Salt River at Jointhead Dam at Phoenix (site 45, pl. 2) is the highest since 1905, when the Salt River carried an unregulated discharge of more than 200,000 ft*/s. The highest dis- charge known for the Salt River since at least 1871 is 300,000 in 1891. The discharge of 66,600 ft*/s of the Agua Fria River below Waddell Dam (site 51) on Feb- ruary 20 is the highest since November 1919, when the unregulated discharge exceeded 105,000 ft*/s (site 51A). Discharges for sites 51A and 51B are computed from the same gage. Releases from the reservoirs on Salt, Verde, and Agua Fria Rivers in February 1980 came after large releases in March through May 1978 and December 1978 through May 1979. The 1978-80 period is the first period since regulation began in which large releases were made in three consecutive years and the first time since 1905 that floods had occurred so frequently. Regulation began in 1910 on the Salt River, in 1927 on the Agua Fria River, and in 1938 on the Verde River, the main tributary to the Salt River upstream from Phoenix. Each of the six storms during February 13-21 caused distinct peaks on small streams. A peak occurred at one or more small streams on each day during the period except February 16 and 20. Each peak was followed by a recession to near base flow. The larger streams had two distinct periods of flood- ing-one February 14-15 and the other February 19-20. During the first, the large streams began rising the morning of February 14 and peaked either late that night or early February 15. The second flood began late February 19, and streams peaked at various times between 2300 hours on February 19 and 1200 hours on February 20. The February 14-15 peak was higher in most of the Salt River basin; the February 19-20 peak was higher in the Little Colorado, Bill Williams, Agua Fria, and Hassayampa River basins and in parts of the Salt River basin. GEOGRAPHIC SETTING The central mountains of Arizona extend in an east- west direction across most of the State. (See pl. 2 for all geographic features named in this discussion.) The moun- tains make up parts of six counties (fig. 1): most of Gila and Yavapai Counties and small parts of Apache, Navajo, Coconino, and Maricopa Counties. The northern slopes of the mountains are drained by tributaries to the Little Colorado River and Havasu Creek. The southern slopes are drained by tributaries to the Salt, Agua Fria, 54 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA + S FIGURE 414. -Santa Ana River at 5th Street bridge in Santa Ana, Calif.: Dry channel prior to February 1980. View from left downstream bank. FIGURE 41B.-Santa Ana River at 5th Street bridge in Santa Ana, Calif., at discharge of about 5,000 cubic feet per second, March 3, 1980. View from right upstream bank. (Photograph courtesy of Orange County Environmental Management Agency.) ARIZONA FLOODS o Pean e ey "_. yz ed C4 r z y e / 55 FIGURE 41C.-Santa Ana River at 5th Street bridge in Santa Ana, Calif.: Extent of damage in late spring 1980. View from left downstream bank. and Hassayampa Rivers, all of which drain to the Gila River. The Bill Williams River heads in the western end of the mountains and drains to the Colorado River. The Salt River, which is the principal stream in the Arizona part of the report area, is formed by the Black and White Rivers. Downstream from the confluence of the Black and White Rivers, five main tributaries-Car- rizo, Cibecue, Canyon, Cherry, and Tonto Creeks- drain from the Mogollon Rim and enter the Salt River in a reach of 90 mi. Each tributary drains 200 to 1,100 mi. The largest tributary is Tonto Creek, which flows directly into Roosevelt Lake. These tributaries all head in or flow through Gila County. The five main tributaries are separated by steeply sloping, sparsely vegetated mountain ranges that extend southward from the Mog- ollon Rim and cause orographic uplift to the eastward- moving storms. The Salt River is joined by its major tributary, the Verde River, 25 mi upstream from Phoe- nix. The Verde River drains from the low mountains west of Williams in Coconino County and flows southeastward through Yavapai and Maricopa Counties to the Salt River. As the Verde River flows through the Verde Valley, it is joined by several tributaries from the Mogollon Rim. These tributaries produce a major part of the runoff in the Verde River. At the confluence of the two rivers, the drainage areas of the Salt and Verde Rivers are about 6,300 and 6,600 mi", respectively. Downstream from the Verde River, the Salt River flows westward through the center of the highly urbanized part of Maricopa County and joins the Gila River west of Phoenix. The Salt River is the main source of flood runoff to the Gila River, which heads in New Mexico and flows across Arizona to join the Colorado River near Yuma. Most of the streams in the mountains flow through well-defined canyons and short reaches of flood plain. The few flood plains are sparsely inhabited and are occupied by an occasional small town or community. Significant flood plains exist along the Verde River, East Verde River, and Tonto Creek and the lower reaches of the Hassayampa River. For some distance downstream from the Verde River, the Salt River flows in a broad braided channel about 0.5 to 1 mi wide, but through central Phoenix the river has a rather well defined channel. Much of that channel has been developed by manmade and natural causes during the past 15 years. Only a small part of the channel existed prior to the flood of December 1965 (Aldridge, 1970). The Salt River is crossed by many streets that connect the southern and northern parts of the metropolitan area. The Agua Fria River heads between Prescott and Camp Verde in Yavapai County and flows southward to join the Gila River west of Phoenix 3 mi downstream from the Salt River. Principal tributaries are Black 56 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 19°15 119° T L. West For 9,” GH t G fa foe Piru Creek Lake (a? ll Casitas (é; & Piru 0 A o Z C z % G got a $ o & « 3 : 4r, + o Ventura Creek "Oto C X C e€ a & C « 00 of: 0 Oxnard oF o igh ie & Pacific Missile <}\ Lake Test Center 45 __J Point Mugu 24 C/p Point Dume e 1216 20s - age ong ___ 117° 2C. sant, i Luis '- OBISPO ~- KERN ( reed | Eras/[33mm SANTA JP a peice an non B BarBARA & V _ tos | QTANGELESJ‘ ous uum nmr Ay 4 _ riversipe _____ |=~~~ - SAN _! IMPERIAL DIEGO i MAP AREA 33° 18°45 118°30° 18°15 Castaic & - que Lake a? *C Castaic x0 /- Santa Felicia Creek 00°?! Dam <0 f Santg Clard iver O’e A= - 34°15 ,o / Hansen Dam Sepulveda __, SAN Flood Control GABRIEL Basin MoUNTAINS Sepulveda Dam a o o ® 3 a g Joins Figure 32 Los Angel Topanga Beach % on he's Malibu Beach 0 Santa Monica OCEAN Manhattan Beach 5 10 MILES 5 10 KILOMETERS 0 Redondo Beach - 33°45 EXPLANATION 44 |___| PHOTOGRAPH LOCATION-Number indicates figure FIGURE 42. -Los Angeles River basin and other major coastal stream basins in Los Angeles and Ventura Counties, Calif. Canyon Creek and the New River. Black Canyon Creek drains the Bradshaw Mountains and enters the Agua Fria River upstream from Lake Pleasant. The New River drains the New River Mountains and enters the Agua Fria River downstream from Lake Pleasant within the urban part of Maricopa County. The Agua Fria River flows through several cities west of Phoenix and sepa- rates much of the metropolitan residential area from downtown Phoenix. From the time regulation began on the Agua Fria River in 1927 to 1978, the river carried a maximum of a few thousand cubic feet per second between Lake Pleas- ant and the New River. During these years of low flow, deposits of alluvium gradually accumulated along the river, and a narrow channel developed. The channel is incised only a few feet below a fairly wide, easily erodible flood plain. Downstream from the Agua Fria River, the channel of the Gila River is overgrown with dense phreatophytes, and extensive flooding occurs during moderate dis- charges. The third major tributary to the Gila River in the study area is the Hassayampa River, which also heads near Prescott and flows southward through west- ern Yavapai County and northwestern Maricopa County to join the Gila River west of Buckeye. The Hassayampa River is unregulated. Four reservoirs on the Salt River and two reservoirs on the Verde River store water for irrigation. The principal reservoir is Roosevelt Lake-above Theodore Roosevelt Dam-on the Salt River just below Tonto ARIZONA FLOODS 57 Creek. Roosevelt Lake has a capacity of 1,337,000 acre-ft. Three downstream reservoirs on the Salt River-Apache Lake above Horse Mesa Dam, Canyon Lake above Mormon Flat Dam, and Saguaro Lake above Stewart Mountain Dam-have a combined capacity of 373,000 acre-ft. Two reservoirs on the Verde River- Horseshoe and Bartlett-have a combined capacity of 309,600 acre-ft. Granite Reef Dam on the Salt River east of Phoenix and Gillespie Dam on the Gila River south of Buckeye-low-head diversion dams near the upstream and downstream limits of the metropolitan area-are the principal points where streamflow into and out of the metropolitan area is computed. Most of the flood damage in Maricopa County occurred between the two dams. Streamflow is also measured at Jointhead Dam, located in Phoenix 20 mi downstream from Granite Reef Dam. Jointhead Dam serves only as a low-flow control for the gaging station. There is no reservoir behind the dam. Lake Pleasant (another reservoir for storing irrigation water) on the Agua Fria River partially controls flood- flows of the Agua Fria River. During most years, all inflow is stored. Water is released to the Agua Fria River only when the volume of water stored in the reservoir approaches the capacity of the reservoir and the inflow is greater than the amount needed for irriga- tion. Flood protection for the lower reaches of the Gila River is provided by Painted Rock Reservoir west of Gila Bend. The reservoir has a capacity of 2.5 million acre-ft. Alamo Reservoir on the Bill Williams River reduces floodflows into the Colorado River. MINOR FLOODS IN LITTLE COLORADO, BILL WILLIAMS, AND UPPER GILA RIVER BASINS Minor floods occurred near Show Low, Winslow, and a few other places in the Little Colorado River basin. Peak discharges occurred on February 15 and February 20, 1980. The second peak was generally higher except near the mouth of the Little Colorado River. At Winslow, the Little Colorado River was high enough on the dikes to cause concern about overtopping or failure, although the dikes held. Minor leakage caused a few inches of water to reach low-lying subdivisions. The peak discharge at Winslow was computed as 28,000 ft*/s. By comparison, the peak in December 1978 was 57,600 ft*/s. Several highways along the north side of the Mogollon Rim were closed because of the flood. High flows occurred throughout the Bill Williams River basin. Large amounts of inflow to Alamo Lake caused the reservoir to reach a high level. An above- normal preflood level had resulted from large carryover storage caused by high flow in 1978 and 1979. The U.S. Bureau of Reclamation was concerned about a possible spill from Alamo Dam and a subsequent spill from Parker Dam on the Colorado River, and the water level in Lake Havasu (above Parker Dam) was lowered in order to provide additional flood control for the lower reaches of the Colorado River. High water, but no outstanding floods, occurred in one or two tributaries to the Gila River upstream from the Salt River. The only significant damage was the washout of approaches to a State highway bridge near the mouth of the San Carlos River. Inflow to San Carlos Reservoir, when added to the high carryover storage from the preceding year, was sufficient to cause that reservoir to spill for the second consecutive year, but the spill did not occur until March 1980. The 1979 and 1980 spills are the first that occurred after the reservoir was constructed in 1929. The Gila River upstream from the Salt River peaked at less than 700 ft"/s, several days after the flood on the Salt River. Peak discharges in the Little Colorado River, Bill Williams River, and upper Gila River basins were generally much less than those in past years; therefore, peak data have not been summarized in this report. Data are given in "Water Resources Data for Arizona, Water Year 1980" (U.S. Geological Survey, 1982). MAJOR FLOODS IN LOWER GILA RIVER BASIN ANTECEDENT CONDITIONS To trace the development of conditions leading to the 1980 floods near Phoenix, it is necessary to start in March 1978, when extremely large volumes of runoff exceeded the unfilled capacity of reservoirs on the Salt, Verde, and Agua Fria Rivers. Water released from the reservoirs in March 1978 caused a severe flood in Phoe- nix, where the Salt River was the highest since 1920 (Aldridge and Eychaner, 1984). Large volumes of runoff during the spring of 1978 kept the reservoirs, which usually begin to drop in April or early May, essentially full until June 1978. The reservoirs on the Salt and Agua Fria Rivers were more than 70 percent full at the end of the 1978 irrigation season; the Verde River reservoirs were 50 percent full. Another period of high water began in November 1978. Runoff in December 1978 again exceeded the capacity of the reservoirs and caused another flood. The December 1978 flood was higher than the March 1978 flood at Phoenix (Aldridge and Hales, 1984). Reservoirs were essentially full in June 1979, and they retained a large volume of water after the irrigation season of 1979. Reservoirs on the Verde and Agua Fria Rivers remained 50 to 70 percent full, and those on the Salt River remained more than 80 percent full. Storms in January 1980 caused above-average runoff that began to fill the reservoirs again. The January storms left large amounts of snow at altitudes above 58 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 43A. -San Gabriel River below Santa Fe Dam, Calif., looking upstream prior to the 1980 flood. about 6,000 ft. Below about 8,000 ft, the snow was extremely dense; that is, a high percentage of the snow was water. Snow surveys on February 1 showed the water content of the snowpack of the Salt River basin to be 148 percent of normal. The soil under the snowpack was saturated. Above-average runoff that followed the January storms continued to increase the contents of reservoirs. The unfilled capacities on February 13 were: Unfilled Reservoir system (521255237 Fzzfizfg’ls (acre-ft) Salt River....................... 1,755,000 194,000 Verde River ...........2.2....... 309,600 36,000 Lake Pleasant (Agua Fria River) ........................ 157,000 3,600 The potential for reservoirs to fill, spill, and cause flooding during any significant storm period was extremely high. The probabilities of the reservoirs filling during a single flood were 1.0 for the Verde and Agua Fria River reservoir systems and about 0.3 for the Salt River reservoir system. SALT RIVER UPSTREAM FROM ROOSEVELT DAM Runoff in the Salt River basin during the February 14-15 flood originated mainly below an altitude of 5,000 ft, although the snowline remained near 7,000 ft during most of the storm period and may have reached 10,000 ft early in the storm period. The high-altitude parts of the basin that had contributed heavily to the December 1978 flood (Aldridge and Hales, 1984) contributed little to the February 1980 flood. Peak discharges on streams drain- ing less than 20 mi" were small relative to past floods from convective summer storms. The relative magnitude of the flood increased as the drainage area increased and flow from large areas concentrated (table 24). Large quantities of runoff came from tributaries to the Salt River between the confluence of the Black and White Rivers and Roosevelt Dam. The peak discharge of the Salt River near Roosevelt (site 11, pl. 2), 99,000 ft*/s, is the third highest since records began in 1913. The high flow combined with a peak of record on Tonto Creek and ARIZONA FLOODS 59 FIGURE 43B.-San Gabriel River below Santa Fe Dam, Calif., looking upstream during February 1980 release. a large inflow from ungaged tributaries to produce a peak inflow to Roosevelt Lake of more than 150,000 ft/s. This is probably the second highest inflow to Roosevelt Lake since storage began in 1910. Most of the inflow to the system of reservoirs on the Salt River is measured at gaging stations on the Salt River near Roosevelt and Tonto Creek above Gun Creek, near Roosevelt (site 14; tables 10, 11). This was the third time in 2 years that the inflow to Roosevelt Lake had exceeded 150,000 ft*/s. To compare inflow rates during floods of March 1978, December 1978, and February 1980, the inflow to the reservoir during each flood was computed from hourly reports of lake levels and reservoir releases. Although 2-hour incre- ments were used in the computation, the computed discharge fluctuated considerably because lake-level readings are affected by wind, gate openings, wedge storage, and observational error. Small variations in lake levels caused large variations in computed discharges. The fluctuations are great enough to make accurate determinations of inflow impossible. Peak inflows com- puted on the basis of 2-hour periods were 170,000 ft*/s on March 2, 1978, 152,000 ft"/s on December 18, 1978, and 167,000 ft"/s on February 15, 1980. The computations do not account for traveltime that would have existed had tributaries been flowing into the Salt River rather than into the reservoir; therefore, they tend tc overestimate the natural flow of the Salt River at Roosevelt Dam. Computations for the flood of March 1978 indicate that peak discharges that would have passed the damsite if the dam did not exist are probably about 10-15 percent less. Four floods of comparable magnitude occurred on the Salt River between 1890 and 1977. Aldridge (1970) reported discharges for the floods as follows: Estimated discharge, Date in cubic feet per second February kkk. 150,000 November 1905. kk. 145,000 March 1941 ekke eee... 140,000 January 1951 ekke. ... 140,000 The volume of water flowing into Roosevelt Lake from Salt River and Tonto Creek-that is, the gaged inflow - was 550,000 acre-ft during the 7 highest consecutive days 60 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA FIGURE 44. -House along Topanga Canyon, Santa Monica Mountains, near Santa Monica, Calif., February 20, 1980. (Los Angeles Times photograph.) during the February 1980 flood period and is the third largest in 7 days since storage began in Roosevelt Lake in 1910 (table 12). Greater 7-day volumes of gaged inflow occurred in January 1916 and March 1978. The total volume of inflow (including ungaged flow) during the 7 highest days in February 1980 was about 740,000 acre-ft and may have exceeded the corresponding volumes in 1916 and 1978. The 7-day volume was particularly high because it encompassed the two periods of high runoff on February 15 and February 20, 1980. The 3-day volume was the fifth largest in the period of record. Table 12 shows several additional periods between 1913 and 1980 when the gaged 7-day inflow to Roosevelt Lake exceeded 200,000 acre-ft. Inflows given in table 12 were computed by summing the daily discharges of the Salt River near Roosevelt and Tonto Creek near Roosevelt for 1913-40 or Tonto Creek above Gun Creek, near Roosevelt for 1941-80. On both streams, records prior to 1925 are from staff gages and have the normal uncertainties associated with staff-gage records. A water-stage recorder was installed on the Salt River in 1925, but the staff gage on Tonto Creek continued in use until December 1940. Thereafter, both streams were equipped with water-stage recorders. There is little likelihood that any inflows exceeded 200,000 acre-ft from 1906 to 1913, but several inflows of this magnitude occurred between the mid-1880's and 1905. Large flows in 1980 from tributaries to the Salt River caused crests at downstream stations on the Salt River to occur before the crest at the upstream station, thereby masking the traveltime between gaging stations (fig. 49). The February 15 flood at the gaging station at Salt River near Roosevelt had one general crest with several minor fluctuations. The highest crest at Salt River near Roosevelt occurred before the single crest upstream at the gaging station at Chrysotile (site 8). The pattern is typical of most floods on the Salt River. VERDE RIVER BASIN UPSTREAM FROM HORSESHOE DAM Both the February 15 and February 20 floods were extremely high in the upper part of the Verde River basin. Some streams had the higher peak on February 15; others had the higher peak on February 20. Within any given geographical area, the date of the higher peak differed from stream to stream. An example is found among streams that drain to the Verde River from the north between Clarkdale and Camp Verde. Woods Can- ARIZONA FLOODS 61 FIGURE 45. -Flooding at Point Mugu, U.S. Naval Air Station, Pacific Missile Test Center, Calif., February 18, 1980. (Photograph courtesy of U.S. Army Corps of Engineers.) yon (site 29), Rattlesnake Canyon (site 31), and Dry Beaver Creek (site 32) had the higher peak on February 14-15; Oak Creek (site 25), Wet Beaver Creek (site 27), Bar M Canyon (site 30), and West Clear Creek (site 34) had the higher peak on February 19-20. Woods Canyon and Bar M Canyon are adjacent basins having similar drainage characteristics. The peak of February 14 on Rattlesnake Canyon is the peak of record. Peaks of February 15 and February 20 exceeded the previous peak of record since 1965 at Williamson Valley Wash near Paulden and since 1963 at Verde River near Paul- den; the February 20 peak was the higher of the two peaks at those stations. The February 15 peak was the higher of the two peaks at all other stations on the Verde River. The peak of record occurred on February 19 or 20, 1980, at Oak Creek near Cornville and at Wet Beaver O bo FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA §300II{NNIIIIIITI{I{II\III[XIIIIIVIIIIIWIIIIIII t -! Precipitation much below normal Precipitation much above normal Precipitation near normal Precipitation much above normal a W LJ - & 280 O c w > pik: > G c CC (C > WW > -E > G c CC (C > W > -k > Go c CC (C > W > - b > o < < B R 3 * 214 333 4g 0 2 07" 3< 3 3 2 @ g 0 2 O7 "* s< 3 3 32 a J 0 2 O o "*~ 3 <4 = 3 2 a [J O 2 1977 1978 1979 1980 FIGURE 47. -Damage to residential structures and severe erosion of beach from surf activity south of Oceanside Harbor breakwater at Oceanside, Calif., February 1980. (Photograph courtesy of U.S. Army Corps of Engineers.) ARIZONA FLOODS 63 g 100,000 T--+T-T-TTTT T-T-TTTT T-T-T-4T-7TTTH A 3 [- A m ® [- O 7 W (- O - & [~ aA - Ac -I [m A A8 5 - F fn - ° { o m 2 A_ [P m 2 19,000 - O gq O 7 5 - A RDH - I |- o€ 7 C [- & o, _ C a 2 Cho 3 = | ao ® - > "4 Z (- - 3 c /A EXPLANATION > 0C, C DATA TAKEN FROM THESE PERIODS th 1,000 |- ©, (@ - g (- O ‘fifl £] /A January - February 1969 - Fe [_ O January - March 1978 - [est - |- January - February 1980 E |_ 0 [] January - February - Bouse C J CS. CTT #0 Io / 1 I ~-~.§_,\_ ...... A\ I‘Vj'!” / \. 20 / bic._. =-- me ( af (eth det" * / "‘ i law L_ / hey h ~, - 20 ofp} _/ ;~" l Verde River below Bartlett Dam \ r- 2427 i (09510000, site 42) ~f 0 Pa L2 a I TCT -| ‘ 1 CI ‘ CI I C F TT C ¢ TT CI ‘ T-I| CI I T-|T CI ‘ T| CI 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 13 14 15 16 17 18 19 20 21 22 FEBRUARY 1980 FIGURE 51. -Discharge of Salt, Verde, and Gila Rivers, Ariz., downstream from reservoirs, February 13-22, 1980. AGUA FRIA AND HASSAYAMPA RIVERS High discharges occurred on the Agua Fria and Has- sayampa Rivers on February 14-15 and 19-20. The February 14-15 flow on the Agua Fria River caused Lake Pleasant to fill and necessitated release of large volumes of water from Waddell Dam (fig. 52). Water reached the mouth of the Agua Fria River about 12 hours after the major release began at Waddell Dam. From February 15 to February 20, outflow from Lake Pleasant was approximately equal to inflow. The peak of record occurred on February 19, 1980, at stations on the Agua Fria River near Mayer (site 47, pl. 2) and Rock Springs (site 50, pl. 2). Data for these stations are given in tables 18 and 19. Inflow to Lake Pleasant was computed by the Maricopa County Metro- politan Water District no. 1 (written commun., 1981) from lake levels and gate openings. Inflow to the lake is equivalent to Agua Fria River above Waddell Dam (site 51A, pl. 2). Peak inflow to Lake Pleasant was 73,300 ft*/s (table 20) and is less than the 79,500 ft*/s computed for the December 1978 flood (Aldridge and Hales, 1984). The lower inflow occurred because Black Canyon Wash and streams tributary to Lake Pleasant had lower peak discharges in February 1980 than in December 1978 and did not peak simultaneously with the Agua Fria River as in 1978. The peak discharges into Lake Pleasant in December 1978 and February 1980 are probably the highest since the reservoir was completed in 1927, but they are considerably less than the peaks of January 1916 and November 1919. The peak discharge in January 1916 was 105,000 The 1919 flood was 3 ft higher than the 1916 flood; discharge was not determined. The volume of runoff into Lake Pleasant during the 7 highest days of the flood period in February 1980 was 220,000 acre-ft. The peak discharge out of Lake Pleasant on February 20, 1980, was 66,600 ft/s, the highest since regulation began. The outflow is equivalent to Agua Fria River below Waddell Dam (pl. 3). The peak discharge decreased to 41,800 ft*/s at El Mirage (Grand Avenue). The New River and other tributaries increased the peak to 44,200 ft*/s at the gage near Avondale (table 21). The rise at Avondale occurred about 8 hours after the major release from Waddell Dam. Locations where bridges were damaged by the Agua Fria River and times when the flood waves of February ARIZONA FLOODS 67 80 Inflow to Lake Pleasant (09513000, site 51A) ---} Release from Lake Pleasant (09513000, site 51B) 20 |- DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND [3 I Agua Fria River near Rock Springs (09512800, site 50) Agua Fria River near Mayer (09512500, site 47) Agua Fria River at Avondale (09513970, site 57) : U i . |I 1 \¢'V'\‘ K ) \ 28 I~. Z '\ \\ £05 . \ 1 ll“-f“/' Y \ a pe. \o © Pos R Cyg 2] & 4 0 ff 2 ce > , oo ll R T «-. , * Z- - 0 I [ I I I N T ‘ I [ | i | [ I ‘ I | I I I I ‘ I ‘ I 1 T [ I ‘ I I I 1200 1200 1200 1200 1200 1200 1200 1200 1200 14 15 16 17 18 19 20 21 22 FEBRUARY 1980 FIGURE 52. -Discharge of Agua Fria River, Ariz., February 14-22, 1980. 14-15 and February 19-20 reached gaging stations on the Agua Fria and Gila Rivers are shown on plate 3. Num- bers 4 through 8 identify parts of the two flood events as follows: 4. When water was first released to the river at Waddell Dam or when water first reached the Avondale station, 5. The leveling off of the release rate on February 14, 6. The crest of the flood of February 15, 7. The beginning of the February 19 rise, and 8. The crest of the February 20 flood. All of the above were identifiable at the Agua Fria River at Avondale gaging station, but only the crest on February 20 was identified on the Gila River down- stream from the Agua Fria, because flow from the Agua Fria mingled with flow from the Salt River. Water was first released into the river downstream from Waddell Dam at 0900 hours on February 14. Small quantities of water released from the reservoir earlier were routed into irrigation canals. Number 4 identifies that release to the river or the time when the first water reached the Avondale station. At Waddell Dam, the release rates represented by numbers 5, 6, and 8 are constant for several hours. Times are for the beginning of that constant rate. These parts of the flood wave can be seen on the hydrograph of release from Lake Pleasant in figure 52. Local residents in the upper part of the Hassayampa basin reported that the river was the highest it had been in many years, but they did not state a specific number of years. At the gaging station at Box damsite near Wick- enburg (site 59, pl. 2), the peak discharge of 24,900 ft"/s is the third highest since 1946. Higher discharges occurred in August 1951 and September 1970 (Roeske and others, 1978). The 1970 discharge of 58,000 ft"/s is considered an extremely rare event. FLOOD DAMAGE The floods caused three deaths in Arizona. One person drowned trying to raft down Oak Creek when it was at flood stage. Two men drowned when their car was washed off a bridge over Granite Creek in Prescott. Preliminary estimates of damage from the February 15 flood amounted to about $1 million each in Gila and Yavapai Counties. Damage in Gila County included destruction of 3,000 ft of sewer line in Miami, flooded boat ramps and campgrounds at Roosevelt Lake, and damage to many roads. All roads from Payson to Phoenix were closed. The estimated cost of repairs to streets in 68 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA Payson was $250,000. Several homes were isolated in the village of Pine. In Yavapai County, about $400,000 damage occurred in Prescott, and more than $500,000 damage occurred in Verde Valley near Bridgeport and Cottonwood. In Sedona, a gasline was cut and the town was without gas for several days. Damage to the gasline was about $150,000. Residents were evacuated along the Verde River, Granite Creek, Oak Creek, Beaver Creek (down- stream from the confluence of Wet Beaver and Dry Beaver Creeks), and West Clear Creek. The flood of February 20 increased the damage in Yavapai County to about $6 million, mostly in the Verde Valley. At Bridgeport, the flood reportedly did less damage than did the March 1978 flood, although the stage was about 0.5 ft higher in 1980. About 15 to 20 rural highways were closed by one or both of the February floods. The most severe damage occurred in the Phoenix area. About 25 streets and highways cross the Salt River between Granite Reef Dam and the mouth of the river; 6 streets cross the Gila River between the Salt River and Gillespie Dam (pl. 3). In February 1980, three of the crossings had large bridges; the remainder had grade- level crossings or small-capacity bridges. The small- capacity bridges were designed to handle a maximum of about 35,000 ft*/s. The floods in March 1978, December 1978, and January 1979 damaged all but two crossings. Most crossings had been put back in service prior to the 1980 flood by replacing approaches or constructing grade-level crossings through the dry streambed. The flood on February 15, 1980, destroyed all grade-level crossings, damaged or destroyed small-capacity bridges and Interstate Highway 10, and brought crosstown traffic to a near standstill. Bridges at Mill and Central Avenues were the only ones crossing the Salt River that were kept open. Traffic jams several miles long and delays of 6 to 8 hours occurred as traffic was funneled across these two bridges. Cross-river traffic dropped from the normal volume of 400,000 vehicles per day to 187,400 per day. Special buses and a commuter train were put into service for 2 weeks until Interstate High- way 10 was reopened. Some bridges were repaired in March, but grade-level crossings were kept closed until flow ceased on June 2, 1980. Following the flood, a concrete pad and cutoff wall were constructed at Inter- state Highway 10 to prevent further scour around piers of the bridges (McDermid and others, 1982). The Salt River flooded the eastern end of the runways at Sky Harbor Airport in Phoenix, washed out sewage- treatment and disposal facilities, destroyed several com- mercial buildings, and damaged gravel operations in the riverbed. Two thousand families were evacuated, and 155 homes reportedly sustained damage. Downstream from the Salt River, the Gila River flooded farmland and the two low-lying subdivisions of Holly Acres and Allen- ville, where an area as much as 2% mi wide was flooded (U.S. Army Corps of Engineers, 1981a). The area flooded by the Agua Fria River on February 20 was as wide as 1/4 mi (Thomsen, 1980; U.S. Army Corps of Engineers, 1981a). The flood inundated two small subdivisions in the rural part of Maricopa County north- west of Phoenix and other residential areas. About 650 families were evacuated from along the Agua Fria River. The flood eroded extensive amounts of channel. Before the flood in February 1980, the river was crossed by 14 major streets and highways between Lake Pleasant and the mouth of the Agua Fria River (pl. 3). Six were bridges, and the rest were grade-level crossings. The flood of February 20 destroyed all grade-level crossings and three bridges and damaged road grades at the other three bridges. Two bridges-Grand Avenue and Glen- dale Avenue-remained open during the flood. About 5 mi above the mouth of the Agua Fria River, the bridge for the continuation of Interstate Highway 10 was under construction, but the embankments had not been con- structed. The river cut a new channel about 4,000 ft to the east of the bridge and bypassed the bridge (fig. 53). Damage in the Phoenix area from the flood amounted to $63.7 million (U.S. Army Corps of Engineers, 1981a). Damage to roads and bridges amounted to $22.0 million; damage to other public facilities amounted to $13.3 million. Other types of losses, in millions of dollars, were transportation delays, $8.4; business and income losses, $5.5; agricultural, $5.0; commercial, $3.1; industrial, $2.8; residential, $1.9; and emergency costs, $1.6 (table 22). The damage was a severe blow to an area that was recovering from damages of $39 million in March 1978 and $52 million in December 1978. The floodwaters scoured most trout streams below an altitude of about 8,000 ft and removed aquatic insect life, moss-covered rocks, rubble, and the mud-covered bot- toms where the trout lie (Avery, 1980). In places, streams were stripped to bedrock. Trees, shrubs, and other riparian vegetation were removed from flood ter- races, and in many places the terraces were removed completely. The scouring caused severe shifting of high- water controls at many gaging stations. POSTFLOOD RESERVOIR RELEASES Several considerations influenced decisions about the magnitude and duration of postflood releases from the Salt and Verde River reservoirs. A need existed for reservoirs to be drawn down enough to allow operators to manage the release of possible subsequent high flows. A strong consideration was the amount that the reser- voirs could be drawn down and still be filled by spring ARIZONA FLOODS 0 1000 2000 3000 FEET | | | ] | I I OT 0 300 600 900 METERS FIGURE 53. -Agua Fria River at Interstate Highway 10 near Avondale, Ariz., February 20, 1980. (Photograph courtesy of Arizona Department of Transportation.) 69 70 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA runoff. Some local governmental agencies wanted flood- waters shut off so that flood damage could be repaired. Other agencies wanted the release kept high to dilute the raw sewage that was pouring into the Salt River from broken sewer lines. Sewer lines remained unusable until April 22, 1980. Releases from the reservoirs were held high enough to keep the discharge past Phoenix above 6,000 ft°/s through February 22. The discharge was decreased gradually from February 23 to March 10. Flow was stopped temporarily on March 10 and was started again on March 27. Small discharges of 2,500 ft*/s or less continued until June 2, when flow ceased. Lake Pleasant, on the Agua Fria River, remained full, and water was released from the reservoir for several weeks after the flood. The release was approximately equal to the inflow. Part of the water released from Lake Pleasant was diverted into irrigation canals at a low-head dam 1 mi downstream from Waddell Dam; the remainder flowed over the diversion dam into the Agua Fria River channel. Water was released over the diversion dam from February 13 to April 13, but the flow reached the mouth of the Agua Fria River only during February 14-26. During the rest of the release period, all flow infiltrated into the streambed. Between January 30 and May 15, 1980, 2.6 million acre-ft of water was released from the reservoirs on the Salt and Verde Rivers. One-half million acre-ft was diverted into canals at Granite Reef Dam, and 2.1 million acre-ft was released to the Salt River below Granite Reef Dam. Another 0.3 million acre-ft was released into the Agua Fria River at the diversion dam below Waddell Dam. About 2.3 million acre-ft reached Gillespie Dam, and 0.1 million acre-ft was lost to infiltration or evapo- ration. During past releases from the reservoirs, much larger quantities of water infiltrated into the ground. The low infiltration rate in 1980 is probably a result of the aquifers having been recharged by the floods in 1978 and 1979 (Mann and Rohne, 1983; Aldridge and Eychaner, 1984; Aldridge and Hales, 1984). In spite of the previous recharge, the water level in wells along the Salt River rose as much as 35 ft near Phoenix and 55 ft near Scottsdale during the 1980 flood. The contents of Painted Rock Reservoir, a flood- control reservoir downstream from Gillespie Dam, reached an all-time high of 1.85 million acre-ft on March 6, 1980. Water was released to the Gila River at a rate that was generally less than 5,000 ft*/s. Releases from the reservoir began on February 7, 1980, and continued through November 1980. Normally, several weeks pass before water released from Painted Rock Dam reaches the mouth of the Gila River, near Yuma. In February 1980, the discharge at the mouth began to increase 5 days after the release began at Painted Rock Dam, because the channel and adjacent land had been saturated by the large quantity of water released during the two preced- ing years. The last of the water stored from floods of December 1978 to March 1979 was released from the reservoir only 1 week before the 1980 release began. From February through November 1980, 2.1 million acre-ft of water was released from Painted Rock Dam; about 76 percent, or 1.6 million acre-ft, reached the mouth of the river. Streamflow losses were about 170,000 acre-ft between Painted Rock Dam and the Mohawk gaging station, 200,000 acre-ft from Mohawk to Dome, and 120,000 acre-ft from Dome to the mouth of the Gila River. Release of water from Painted Rock Reser- voir for a long period caused flooding and waterlogging of extensive areas of farmland along the Gila River near Wellton and Mohawk. Water-level measurements in wells near the Gila River downstream from Painted Rock Dam show water-level increases of as much as 22 ft between January 1980 and January 1981. The sustained flow from the Gila River was added to water released from reservoirs on the Colorado River and caused the Colorado River to incise a new connection to the Gulf of California through sandbars near the mouth in Mexico (Hodge, 1980). For the preceding two decades, water had rarely reached the gulf because storage in upstream reservoirs and many diversions along the Colorado River depleted the flow. In the early stages of the channel cutting that occurred in 1980, water flooded hundreds of acres of farmland and several vil- lages that had developed on the Colorado River delta during the two decades of no flow. RECURRENCE INTERVALS OF PEAK DISCHARGES The probability of a given discharge being equaled or exceeded in any given year is frequently used as an indication of a flood's severity. The severity can also be expressed in terms of recurrence interval, which is the reciprocal of the probability. A discharge that will be equaled or exceeded on an average (over a long period of time) of once in 10 years and has a recurrence interval of 10 years is termed a "10-year flood" and has a probability of 0.1. A 100-year flood has a recurrence interval of 100 years and a probability of 0.01. Recurrence intervals of floods of February 1980 in both California and Arizona differ greatly from site to site. The recurrence intervals for floods in southern California range from 2 to more than 100 years (table 23). Peak discharges with the highest recurrence intervals (lowest probabilities) occurred in the Salton Sea, Tijuana River, and San Luis Rey River basins. One small stream in the Santa Ana River basin-Bautista Creek (site 64, pl. 1)-also had a flood with a recurrence interval greater PHOTOGRAPHIC COVERAGE 71 than 100 years. At most stations on principal streams in the Salt River basin, the recurrence interval for the February 1980 peak discharges ranges from 20 to 25 years; for the Agua Fria River near Mayer, the recur- rence interval is greater than 100 years (table 24). Part of the variation among stations can be explained by the nonuniform distribution of runoff, but there is also a large degree of uncertainty in the computed recurrence intervals. Values given in tables 23 and 24 have been computed mainly from records for the respective gaging stations rather than from any of the regional frequency relations that have been developed (Patterson and Som- ers, 1966; Young and Cruff, 1967; Arizona Water Com- mission, 1973; Waananen and Crippen, 1977; Roeske, 1978). The uncertainty is largely a function of the period over which the records were collected. Many of the records cover only the last 15-25 years. During this period, high flood peaks have occurred more frequently, especially in Arizona, than during the preceding 40 years. Frequency estimates based on data collected mainly during this wet period indicate discharges for given recurrence intervals that are up to three times greater than those computed from long-term records that included many of the dry years. Also, many streams are regulated. Operational patterns are not adequately defined to permit recurrence intervals to be computed for peak discharges on most regulated streams. SUMMARY OF FLOOD STAGES AND DISCHARGES Maximum gage heights (stages) and discharges during the 1980 floods at continuous-recording stations, crest- stage stations, and miscellaneous sites are summarized in table 23 for California and table 24 for Arizona. The tables also show how these maximums compare with the previously known maximums. The number in column 1 of each table identifies the site on plate 1 or 2. The second column is the U.S. Geological Survey downstream order number. The column headed "Period" shows the calendar years for which gage heights or discharges shown in the seventh and eighth columns are known to be a maximum. The period of record does not necessarily correspond to the period during which continuous records of discharge were obtained. Where available, records of historical floods are included, as are years when records may have been collected at other sites on the same stream. Years during which large floods may have occurred, but are not recorded, may be omitted even though some record of low to medium discharges may have been obtained during that year. For some sites, two or more periods are given. A comma between the periods indicates a break in the period of record. Peak discharges during the intervening period are unknown. It is possible that one or more peaks during that period exceed the maximums shown in the seventh and eighth columns. One maximum gage height and (or) discharge is given for the entire period. No comma is used where the first period repre- sents unregulated discharges and the second, regulated. For this case, a maximum is given for each period. The sixth column shows the calendar year during which the maximum occurred. Separate listings are made when maximum discharge and gage height did not occur con- currently. Also, separate listings are given for periods having different degrees of regulation. The last four columns present data for the maximums in February 1980. The data include the day in February on which the maximum occurred, maximum gage height, maximum discharge, and the recurrence interval of the maximum discharge. More detailed information is given in "Water Resources Data for California, Water Year 1980" (U.S. Geological Survey, 1981) and "Water Resources Data for Arizona, Water Year 1980" (U.S. Geological Survey, 1982). PHOTOGRAPHIC COVERAGE Part of the U.S. Geological Survey's flood plan in its major offices in southern California is to coordinate photographic documentation of floods, and to communi- cate frequently with other Federal, State, and local agencies to increase coverage and reduce duplication of effort. During the February 1980 floods, communication and coordination activities were very successful and resulted in flights over a large number of rivers to obtain aerial photography. Most areas of significant flooding were photographed. The Geological Survey not only coordinated the activities for the flood photographic functions, but also contracted for aerial photography on several reaches of rivers in San Diego County. Agencies other than the Geological Survey handled coordination in Arizona. The Arizona Department of Transportation photographed flood areas in the metropolitan part of Maricopa County. Some photographs were taken by private companies. Large numbers of photographs from both ground and air were taken by newspapers, televi- sion stations, and government agencies. Table 25 lists known aerial photographic coverage available from government agencies for the floods dis- cussed in this report. Data were either furnished directly by the ageney or made available for tabulation by U.S. Geological Survey personnel. All photography is in the files of the originating agency. 72 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA SUMMARY Severe floods occurred in the coastal basins of south- ern California and in central Arizona after six Pacific storms struck the Southwestern United States during February 13-21, 1980. The storms were preceded by large amounts of precipitation in January, when many places received two to four times the average. The floods caused 18 deaths and more than $500 million damage in California. Seven southern California counties that were hard hit by floods, mudflows, slope failures, and beach erosion were declared eligible for Federal disaster aid. San Diego and Los Angeles Counties were hit especially hard. The floods caused three deaths and about $80 million damage in Arizona. Outstandingly high discharges occurred spottily near and south of Los Angeles, Calif., and downstream from reservoirs on the Salt, Verde, and Agua Fria Rivers in Arizona. On many streams, the peaks were the highest in 40 to 60 years but less than the highest known. At least one stream had a higher discharge in 1980 than during the 1916 flood, which is the most widespread and highest known flood during the 20th century in southern Califor- nia. Two streams that drain to the Salton Sea had extreme peaks. The peak discharge of San Felipe Creek near Julian is almost six times the former peak of record, and that of Palm Canyon Creek near Palm Springs is nearly twice the previous peak of record. The peak discharge on the Tijuana River near Nestor, Calif., was 89 percent greater than the peak of record between 1936 and 1979. In Arizona, peaks of record occurred at a few gaging stations on unregulated streams for which the period of record is relatively short. Floods that occurred upstream from Roosevelt Lake on the Salt River and Horseshoe Reservoir on the Verde River had been exceeded three to five times over the past 100 years and were of a magnitude that would occur on an average of about once every 20 to 30 years. The meteorological circulation pattern immediately preceding the February storms was characterized by a strong 500-mb ridge over Alaska and a trough extending from about 50° N. latitude and 158° E. longitude to 30° N. and 143° W. Low pressure dominated the northeastern Pacific. A cold airmass moved into the Pacific from Siberia, and a strong temperature gradient developed between there and the tropics. Pacific subtropical west- erly winds were strong enough to displace the Great Basin High and to divert storms into a path over southern California. Rapid increases in precipitable water, average relative humidity, and the K index, along with a decrease in the lifted index, indicated a very unstable weather structure. Short-wave perturbations moved through long-wave patterns as storm centers were continually generated to the north of the jetstream. On February 12 and 13, a subtropical jetstream formed and penetrated below the Alaskan ridge, and over a period of 9 days it brought six short-wave troughs, and the associated storm systems, to the Southwestern United States. As each storm moved through California another formed over the Pacific. Thunderstorms of high water content were embedded in the cloud systems and produced large amounts of rain. A ridge of high pressure had developed over the central Pacific by February 21 and diverted subsequent storms to a more northerly track. The storms produced an average of 5 to 10 in of rain in the coastal plains and valleys of California and 15 to 30 in over the mountains. Most stations in the central moun- tains of Arizona received 3 to 12 in. In Arizona, the precipitation fell mostly as snow above an altitude of about 7,000 ft. In places, the water equivalent of the snowpack increased as much as 15 in during the Febru- ary storms. Precipitation amounts for periods of 24 hours or less had recurrence intervals of 5 to 10 years, but 10-day totals exceeded the 100-year rainfall at some stations. The large cumulative amount of precipitation was more instrumental in producing floods than was any short period of extreme rainfall. The volumes of runoff over 7 and 15 days in many streams south of Los Angeles in California are the highest ever recorded. The 7-day volumes on the Salt and Verde Rivers in Arizona are, respectively, the third and second highest since at least 1906. The above-average volumes of runoff caused all reser- voirs in San Diego County except Lake Henshaw to spill. The newer reservoirs spilled for the first time, and the older ones spilled for the first time in several decades. Seven conservation reservoirs on the Salt, Verde, and Agua Fria Rivers in Arizona filled and spilled for the third consecutive year. Inflows during the floods were several times greater than the unfilled capacities at the start of the floods. Releases from the Salt and Verde River reservoir systems on February 15 caused the Salt River at Phoenix to have the highest discharge since 1905. Releases from Lake Pleasant on February 20 caused the Agua Fria River to have the highest dis- charge since 1919. The San Diego River flowed 7 ft deep through Mission Valley in San Diego. Thousands of individuals were evacuated as businesses, shopping centers, and hotels were flooded. The San Jacinto River, which in the past was diverted to the northeast around the city of San Jacinto in Riverside County, reverted to its former channel through the city. Lake Elsinore, which is fed by the San Jacinto River, rose 19 ft after February 13, 1980, and reached a maximum level of 1,265.7 ft. The surface area of the lake increased from about 6 mi" before the floods to 10 mi" SELECTED REFERENCES 73 after them. Water flowed out into Temescal Wash for the first time since 1917. The lake flooded or otherwise affected 874 buildings; 300 permanent structures were damaged, and about 400 mobile homes and trailers were relocated. 6 A large industrial complex about 0.8 mi north of San Luis Rey Mission was inundated when a levee along the San Luis Rey River broke. The Santa Margarita River eroded long reaches of bank and destroyed sections of the railroad at Camp Joseph H. Pendleton Marine Corps Base. The Santa Ana River scoured its bed to depths of 20 ft and caused the concrete bank lining to give way. Severe scour occurred around the supports of six major bridges in the city of Santa Ana. Flood damage was extensive in small basins between the Los Angeles and Santa Clara Rivers. Parts of the Point Mugu, U.S. Naval Air Station, Pacific Missile Testing Center were flooded. Mudflows and slope failures were prevalent in Los Angeles and San Bernardino and to the north of Los Angeles. Mudflows were especially severe in basins that had been denuded by intense fires during the preceding year. High winds and wave action caused severe coastal damage, and broken sewer lines caused beach contami- nation. A number of homes and small hotels at Oceanside were damaged by surf and wave action, and the beach was reduced to a cobble pavement. Coastal residents near Marina Del Rey, in Los Angeles, suffered heavy damage from an 8- to 9-ft surf on one side of their property and flooding and mudslides on the other. About 150 ft of seawall was lost at Sea Cliff State Beach. Beaches near Imperial Beach, Calif., were quarantined for 14 months because of sewage carried to the ocean by the Tijuana River. Approximately 65 mi of beach in Los Angeles County was closed for 3 weeks because raw sewage from a broken line in Agoura was carried to the ocean by Malibu Creek. Most of the flood damage in Arizona occurred in Maricopa County, where streets and roads that cross the Salt, Gila, and Agua Fria Rivers were destroyed. Only two bridges over the Salt River and two over the Agua Fria River remained open during and following the floods. More than 2,600 families were evacuated from along the Salt and Agua Fria Rivers. The floods severely damaged trout streams, and the Colorado River in Sonora, Mexico, cut a new channel through sand bars that had blocked the mouth of the river for two decades. From February to May 1980, 2.6 million acre-ft of water was released from the Salt and Verde River reservoirs (of which 0.5 million acre-ft was diverted into canals at Granite Reef Dam) and 0.3 million acre-ft was released from Lake Pleasant; 2.3 million acre-ft reached Gillespie Dam. The storage in Painted Rock Reservoir (for flood control) reached an all-time maximum of 1.85 million acre-ft on March 6, 1980. Water was released from the reservoir for 10 months at a maximum dis- charge of about 5,000 ft*/s. A total of 2.1 million acre-ft was released from Painted Rock Dam; 1.6 million acre-ft reached the mouth of the Gila River. The prolonged high flows contributed to extreme amounts of recharge to aquifers, especially those within a few miles of major stream channels. Ground-water levels rose as much as 55 ft along the Salt River in Scottsdale, Ariz. In one well near the San Gabriel River east of Los Angeles the water level rose nearly 34 ft between January and June 1980. SELECTED REFERENCES Aldridge, B.N., 1963, Floods of August 1963 in Prescott, Arizona: U.S. Geological Survey open-file report, 12 p. 1970, Flood of November 1965 to January 1966 in Gila River basin, Arizona and New Mexico, and adjacent basins in Arizona: U.S. Geological Survey Water-Supply Paper 1850-C, 176 p. Aldridge, B.N., and Eychaner, J. H., 1984, Floods of October 1977 in southern Arizona and March 1978 in central Arizona: U.S. Geolog- ical Survey Water-Supply Paper 2223, 143 p. Aldridge, B.N., and Hales, T.A., 1984, Floods of November 1978 to March 1979 in Arizona and west-central New Mexico: U.S. Geo- logical Survey Water-Supply Paper 2241, 149 p. Arizona Water Commission, 1973, Floodplain delineation criteria and proceedings: Arizona Water Commission Report 4, 12 p. Avery, Ben, 1980, State flood damage severe, but trout streams surviving: The Arizona Republic, March 14, 1980, p. D7. Bartfield, Ira, and Taylor, D.B., 1982, A case study of a real-time flood warning system on Sespe Creek, Ventura County, California, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Labora- tory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 165-176 [available from National Academy Press]. California Department of Natural Resources, 1954, Geology of south- ern California: California Department of Natural Resources Bul- letin 170, Chapter 1, General Features, 53 p. California Department of Water Resources, 1957, The California water plan: California Department of Water Resources Bulletin 3, 246 p. (reprint) 1980, California flood management: An evaluation of flood damage and prevention programs: California Department of Water Resources Bulletin 199, 277 p. Cooper, W. S., 1967, Coastal dunes of California: The Geological Society of America Memoir 104, 131 p. Davis, J.D., 1982, Rare and unusual postfire flood events experienced in Los Angeles County during 1978 and 1980, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 243-256 [available from National Academy Press]. Edwards, K.L., 1982, Failure of the San Jacinto River levees near San Jacinto, California, floods of February, 1980, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: 7A FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA Symposium, September 17-18, 1980, Proceedings, p. 347-356 [available from National Academy Press]. Evelyn, J.B., 1982, Operation and performance of Corps of Engineers flood control projects in southern California and Arizona during 1978-80, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 131-150 [available from National Academy Press]. Franklin, E., Moreland, R., and Lao, P., 1981, Hydrologic data report 1979-1980 season: Orange County (Calif.) Environmental Manage- ment Agency, v. 16, 129 p. Gray, T.I., Jr., Irwin, J. R., Krueger, A.F., and Varnador, M.S., 1976, Average circulation in the troposphere over the tropics, January 1968-August 1972: U.S. Department of Commerce, National Oce- anic and Atmospheric Administration, 110 p. Hely, A.G., Hughes, G.H., and Irelan, Burdge, 1966, Hydrologic regimen of Salton Sea, California: U.S. Geological Survey Profes- sional Paper 486-C, 32 p. Hodge, Carle, 1980, Colorado River again pouring into gulf along ancient course: The Arizona Republic, March 30, 1980, p. C1-C2. Mann, L.J., and Rohne, P. B., Jr., 1983, Streamflow losses and changes in ground-water levels along the Salt and Gila Rivers near Phoe- nix, Arizona, February 1978 to June 1980: U.S. Geological Survey Water-Resources Investigations Report 83-4043, 15 p. McDermid, R.M., Geiser, G.J., Simons, D. B., and Li, Ruh-Ming, 1982, Flood control work on the Salt River in Phoenix, Arizona, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Labora- tory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 401-411 [available from National Academy Press]. McGlashan, H. D., and Ebert, F.C., 1918, Southern California floods of January 1916: U.S. Geological Survey Water-Supply Paper 426, 80 p. Miller, J. F., 1964, Two- to ten-day precipitation for return periods of 2 to 100 years in the contiguous United States: U.S. Department of Commerce, Weather Bureau Technical Paper 49, 29 p. Miller, J.F., Frederick, R.H., and Tracey, R.J., 1973, Precipitation- frequency atlas of the Western United States: U.S. Department of Commerce, National Oceanic and Atmospheric Administration Atlas 2, v. 8 for Arizona, 41 p., and v. 11 for California, 71 p. 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R., 1982, Comment on peak floodflows in San Diego's Mission Valley, 1978-80, in National Research Council Committee on Natural Disasters and California Institute of Technology Environ- mental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 205-206 [available from National Academy Press]. Roeske, R.H., 1978, Methods for estimating the magnitude and fre- quency of floods of Arizona: Arizona Department of Transportation Report ADOT-RS-15(121), 81 p. Roeske, R.H., Cooley, M.E., and Aldridge, B.N., 1978, Floods of September 1970 in Arizona, Utah, Colorado, and New Mexico: U.S. Geological Survey Water-Supply Paper 2052, 135 p. San Diego County Department of Sanitation and Flood Control, 1975, Storms in San Diego County: San Diego County (Calif.) Depart- ment of Sanitation and Flood Control, 19 p., 6 app. San Diego County Flood Control District, 1980, Storm report February 1980: San Diego County (Calif.) Flood Control District report, 26 p. Sciandrone, Joe, and others, 1982, Levee failures and distress, San Jacinto River levee and Bautista Creek channel, Riverside County, Santa Ana River basin, California, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 357-386 [available from National Academy Press]. Scott, M.B., 1977, Development of water facilities in the Santa Ana River basin, California, 1810-1968: U.S. Geological Survey Open- File Report 77-398, 231 p. 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M., 1982, The Santa Barbara County flood experience in storms of 1978 and 1980, in National Research Council Committee on Natural Disasters and California Institute of Technology Envi- ronmental Quality Laboratory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 257-270 [available from National Academy Press]. Taylor, D. V., 1982, Floodflows in major streams in Ventura County, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Labora- tory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 151-164 [available from National Academy Press]. Thomsen, B.W., 1980, Flood of February 1980 along the Agua Fria River, Maricopa County, Arizona: U.S. Geological Survey Open- File Report 80-767, 1 sheet. 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White, C.R., 1982, Lake Elsinore flood disaster of March 1980, in National Research Council Committee on Natural Disasters and California Institute of Technology Environmental Quality Labora- tory, Storms, floods, and debris flows in southern California and Arizona, 1978 and 1980: Symposium, September 17-18, 1980, Proceedings, p. 387-400 [available from National Academy Press]. Young, LE., and Cruff, R.W., 1967, Magnitude and frequency of floods in the United States, Part 11, Pacific slope basins in California, Volume 1, Coastal basins south of Klamath River basin, and Central Valley drainage from the west: U.S. Geological Survey Water-Supply Paper 1685, 272 p. TABLES 1-25 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TABLE 1. -Meridional-temperature gradient, per 10 degrees of latitude, observed at 0400 hours P.s.t., February 15, 1980, compared with long-term climatological averages for February (in parentheses) over the Pacific Ocean at various pressure levels [In degrees Celsius. mb, millibar] Longitude ... 140° E. 160° E. 180° W. Latitude. .... 20-30° N. 30-40° N. 20-30° N. 30-40° N. 20-309 N. 850 mb 13 (9) 18 (13) 9 (7) 13 ( 8) 9 (5) 700 mb 12 (9) 20 (15) 9 (7) 18 (13) 7 (6) 500 mb 6 (6) 25 (17) 7 (6) 22 (12) 3 (7) Longitude ... 180° W. 160° W. 140° W. Latitude. .... 30-40° N. 20-30° N. 30-40° N. 20-30° N. 30-40° N. 850 mb 12 (7) 11 (4) 4 (5) 9 (4) 5 (4) 700 mb 19 (9) 12 (4) 6 (1) 9 (7) 6 (5) 500 mb 24 (9) 11 (6) 12 (6) 12 (6) 5 (5) NOTE.--Climatological averages of meridional-temperature gradient, shown in parentheses, were derived from "Selected Level Heights, Temperatures and Dew Points for the Northern Hemisphere" NAVAIR-50-1C-52, published by direction of Commander, Naval Weather Service, for sale by Government Printing Office, Washington, D.C. TABLES TaBur 2. -Precipitation at selected stations in southern California and Arizona during January and February 1980 [February maximum daily: Amount is for date (24-hour period) indicated by number in parentheses; for example, (17/0600) indicates rainfall during the 24-hour period ending at 0600 hours on February 17. Climatic divisions shown in fig. 13. California stations shown in fig. 14. Arizona stations shown in fig. 15. --, data not available] January February Eleva Depar- Depar- Maximum Feb. Station Latitude - Longitude tion Total ture Total - ture dail 13-22 (deg min) (deg min) (ft) (in) from (in) from - Amount Date amount normal normal (in) (in) (in) (in) CALIFORNIA South Coast Drainage climatic division Burbank Valley pumping | 34 11 118 21 6550 7.43 4.28 14.45 11.36 5.60 (17/0600) 14.45 plant Campo 32 38 116 28 2,630 11.82 9.40 8.82 6.52 2.72 (18) 8.82 Chula Vista 32 36 117 05 9 4.72 3.11 2.24 . 97 .60 (18) 2.24 Cuyamaca 32 59 116 35 4,640 22.37 16.78 22.90 17.49 5.90 (21/1200) 22.90 Henshaw Dam 33 14 116 46 2,700 18.77 14.54 _ 21.40 17.67 3.85 (20) 21.40 La Mesa 32 14 117 01 530 9.70 7.49 7.43 5.51 1.87 (21) 7.43 Long Beach 33 49 118 09 34 7.17 4.91 9.40 7.24 2.37 (16) 9.37 Los Angeles Airport 33 56 118 23 100 _ 9.97 4.45 9.13 6.81 2.63 (13) 9.13 Los Angeles Civic Center 34 03 118 14 257 7.50 4.50 12.75 9.98 3.03 (16) 12.75 Lytle Creek Ranger 34 14 117 29 2,730 26.12 18.70 30.89 24.82 6.60 (14/1100) 30.89 Station Mt. Wilson 2 34 14 118 5,709 21.01 14.66 30.71 24.65 5.42 (16) 30.71 Palomar Mt. Observatory - 33 21 116 52 5,550 18.63 13.78 - 23.10 18.44 5.20 (21/1000) 23.10 Pasadena 34 09 118 09 864 11.10 7.09 19.70 15.87 3.53 (15) 19.70 San Diego 32 44 117 52 13 5.58 3.70 4,47 2.99 1.41 (20) 4,47 San Gabriel Dam 34 12 117 52 1,481 18.96 12.89 26.76 21.58 7.75 (17) 26.76 Topanga Patrol Station 34 05 118 36 745 12.30 6.50 17.00 12.37 8.30 (17) 17.00 Torrance 33 48 118 20 110 _ 8.90 6.16 9.57 7.01 1.98 (18) 9.57 UCLA 34 04 118 27 430 7.35 3.49 18.37 14.74 4.14 (18) 18.37 Southeast Desert Basins climatic division Crestline Fire Station 34 14 117 18 4,900 14.40 -- - 30.10 -- 6.80 (17/0600) 30.10 Lake Arrowhead 34 15 117 11 5,205 22.15 14.01 24.26 16.64 4.55 (21) 24.26 Palmdale 34 35 18 06 2,596 - 3.14 1.66 6.42 5.05 1.46 (14) 6.42 Palm Springs 33 50 116 30 42500 4.14 3.01 5. 41 4.75 1.14 (14) 5.41 ARIZONA Northwest climatic division Truxton Canyon 35 23 113 40 3,820 2.47 1.61 2.43 1.44 0.60 (14) 2.43 Tuweep 36 17 113 04 4,775 - 3.62 2.52 3.89 - 2.99 .70 (14, 19) 3.89 Northeast climatic division Flagstaff 35 08 111 40 7,006 _ 6.52 4.63 7.81 6.34 2.37 (14) 7.81 Fort Valley 35 16 111. 44 7,347 5.66 5.60 6.44 4.78 2.00 (14) 6.42 Junipine 34 58 111. 45 5,134 10.13 7.34 13.94 11.67 2.90 (14) 13.94 Winslow 35 01 110 44 4,890 _ 1.18 .76 1.36 . 98 .57 (19) 1.36 North Central climatic division Childs 34 21 111. 42 2,650 7.43 5.64 9.17 7.90 2.77 (20) 9.14 Crown King 34 12 112 20 5,920 13.54 10.56 16.63 14.38 3.71 (20) 16.53 Jerome 34 45 112 07 5,245 6.30 4.74 8.42 7.06 1.96 (15) 8.35 Prescott 34 34 112 28 5,510 _ 5.91 4.21 6.59 5.23 2.35 (15) 6.59 Seligman 35 19 112 53 5,250 - 3.1 2.21 2.70 _ 1.99 .70 (20) 2.70 Walnut Grove 34 56 112 49 5,090 5.51 4.16 5.30 4.19 2.31 (14) 5.30 East Central climatic division Miami 33 24 10 53 3,560 _ 4.16 2.10 8.11 6.86 2.32 (15) 8.11 Pleasant Valley 34 06 110 56 5,050 _ 5.60 3.65 7.20 5.93 2.01 (15) 7.20 Southwest climatic division Parker 34 10 114 17 425 1.78 1.25 2.36 2.04 0.66 (14) 2.36 South Central climatic division Bartlett Dam 33 49 111 38 1,650 _ 5.39 4.00 8.57 7.60 2.61 (19) 8.57 Florence 33 02 111 23 1,505 2.46 1.53 2.46 1.65 .85 (15) 2.43 Mormon Flat 33 33 111 27 1,715 4.04 2.58 5.07 4.03 1.20 (16) 5.07 Phoenix Airport 33 26 112 01 1,110 _ 1.58 .87 2.09 - 1.49 79 (15) 2.09 Superior 33 18 111 06 2,995 4.10 1.95 6.04 4.64 1.23 (15) 6.01 Wikenburg 33 59 112 44 2,095 3.21 2.19 5.00 4.04 1.20 (14) 5.00 Southeast climatic division Ajo 32 22 112 52 1,800 0.64 -O0 . 06 1.57 1.04 0.75 (16) 1.56 Clifton 33 03 109 17 3,460 - 1.15 . 20 3.55 - 2.93 ~~ -- 3.55 Duncan 32 45 109 07 3,660 .80 .01 3.12 2.53 1.36 (14) 1.96 Palisade Ranger Station 32 25 110 43 7,945 5.70 -- 10.81 -- 4.83 (14) 9.32 Sabino Canyon 32 18 110 49 2,640 _ 1.65 .60 3.47 _ 2.65 .99 ( 8) 2.31 Tucson Airport 32 08 110 57 2,584 .73 -. 04 2.90 2.20 .86 ( 8) 2.04 79 80 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBuE 3. -Average precipitation and departure from normal in California and Arizona during January and February 1980, by climatic division [Climatic divisions shown in fig. 13] January February Climatic Depar- Percent Depar- Percent division Mean ture of Mean ture of (in) (in) normal (in) (in) _ normal CALIFORNIA North Coast Drainage 7.38 -1.11 87 9.30 3.54 161 Sacramento Drainage 8.92 2.04 130 11.19 5.78 207 Northeast Interior Basins 8.61 4.79 225 7.01 4,26 255 Central Coast Drainage 5.54 1.26 129 7.13 3.83 178 San Joaquin Drainage 8.26 4.73 234 6.50 3. 48 215 South Coast Drainage 9.21 6.12 298 11.82 8.96 413 Southeast Desert Basins 3.04 1.77 239 4,26 3.12 374 ARIZONA Northwest 3.19 2.34 375 2.98 - 2.09 335 Northeast 3.64 2.54 331 4.05 _ 3.16 455 North Central 5.97 4.62 442 6.58 - 5.41 562 East Central 4.69 2.68 233 7.05 _ 5.70 522 Southwest 1.12 0.65 238 1.56 _ 1.20 433 South Central 2.33 1.38 245 3.11 2.34 404 Southeast 1.21 0.27 129 2.90 - 2.17 397 TABLES TaBue 4. -Comparison of precipitation amounts observed during the storms of February 1980 with estimated 100-year amounts at selected stations in southern California and Arizona [In inches. Stations shown in figs. 14 and 15. --, data not available] Station 24 hour 1 day 10 day Observed 100 yr Observed 100 yr Observed 100 yr CALIFORNIA Burbank Valley 5. 60 8.0 4.15 -- 14.45 17.0 pumping plant Crestline Fire 6.80 17.0 -- -- 30.10 32.0 Station Cuyamaca 5.90 13.0 3.03 =- 22.90 19.5 Henshaw Dam -- -- 3.85 7.1 21.40 20.0 Lake Arrowhead -- -- 4,55 15.9 24.26 30.0 Mt. Wilson 2 &~ -- 5. 42 16.1 30.71 29.0 Palomar Mt. 5.20 11.0 4.09 -- 23.10 20.0 Observatory San Gabriel Dam -- -- 7.75 12.8 26.76 30.0 Topanga Patrol -- -- 8.30 10.8 17.00 21.0 Station UCLA a e 4.14 -- -- -- ARIZONA Childs -- -- 2.77 -- 4,2 9.14 Crown King -- -- 3.71 5.8 16.63 9.0 Junipine -- -- 2.90 4.9 13.94 8.0 Palisade Ranger -- -- 4.83 -- 4,2 9.32 Station 81 82 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBL® 5.-Peak discharges at selected gaging stations during major floods in southern California [For peak discharges prior to 1916, year is indicated in parentheses. Sites shown on pl. 1. --, data not available] Drainage Peak discharge in indicated year, area, in cubic feet per second Site Station name in Prior - square _ to 1916 1916 1927 1938 1969 1978 1980 miles 20 Sweetwater River near 45, 4 -- 9,870 11,200 -- 1,750 1,150 6,750 Descanso 21 San Diego River near 377 -- 70,200 45,400 7,350 1,830 3,010 3, 420 Santee 27 Santa Ysabel Creek near 112 -- 28 , 400 -- -- 6,180 4,000 10,700 Ramona 29 Santa Maria Creek near 57.6 -- 7,140 -- -- 1,400 2,850 15,200 Ramona San Luis Rey River: 33 at Monserate Narrows, 373 -- 275,000 -- ~- 3,250 4,340 _ 15,500 near Pala 35 at Oceanside 558 2128,000 95,600 -- 16,500 - 11,500 9,780 25,000 (1891) 40 Santa Margarita River at 740 -- -- 33,600 31,000 19,200 21,200 24,000 Ysidora 41 San Juan Creek at San 117 -- ~~ inter 13,000 - 22,400 14,700 _ 11,400 Juan Capistrano Santa Ana River: 46 near Mentone 210 53,700 29,100 24,000 52,300 - 15,300 2,170 5,930 (1891) 62 at Riverside Narrows, 855 320,000 -- -- 100,000 41,000 19,500 19,500 near Arlington (1862) 47 Mill Creek near Yucaipa 42, 4 =- -- 4,500 18,100 _ 35,400 5, 400 35,550 49 City Creek near Highland 19.6 -- -- 1,930 6,900 7,000 2,510 - 33,630 52 East Twin Creek near 8.8 -- -- 480 3,360 2,300 1,480 _ 33,710 Arrowhead Springs 66 San Jacinto River near 723 -- 14,000 16,000 2,790 6,260 6,270 9,010 Elsinore 77 San Gabriel River below 236 -- - *40,000 418,200 465,700 30,900 14,200 18,500 Santa Fe Dam, near Baldwin Park Los Angeles River: 82 at Sepulveda Dam 158 -- -- -- 12,000 13,800 14,700 15,100 87 at Long Beach 827 -- -- -- 99,000 102,000 94,800 129,000 84 Arroyo Seco near Pasadena 16.0 -- 3,150 1,400 8,620 8,540 5,360 3,080 97 Sespe Creek near Fillmore 251 -- - 518,600 -- 56,000 60,000 73,000 40,700 98 Santa Paula Creek near 40.0 -- -- -- 13,500 21,000 16,000 11,800 Santa Pala 99 Santa Clara River at 1,612 -- -- -- 120,000 165,000 102,000 81,400 Montalvo 106 Ventura River near 188 -- -- -- 39,200 58,000 63,600 37,900 Ventura 126 Santa ¥nez River at 789 120,000 -- -- 45,000 80,000 63,200 16,300 Narrows, near Lompoc (1907) 133 Sisquoc River near Sisquoc _ 281 -- -~ -- 11,000 _ 21,400 _ 15,900 5,120 1 Near Pala, drainage area 317 mi'. 2 Near Bonsall, drainage area 513 mi'. 3 Maximum in 1980 occurred January 29. 4 Near Azuza, drainage area 214 mi. 5 Near Sespe, drainage area 210 mi. TABLES TABLE 6.-Mean discharges for 7 and 15 consecutive days at selected sites in southern California during floods of 1980 [Average flows for highest 7 and 15 consecutive days; rank of 1 indicates highest event during period of record, 2 indicates second highest, and so forth. Flows in 1980 began during the period February 13-19. Sites shown on pl. 1. Mean discharge in cubic feet per second] 83 Period High 7 days High 15 days of daily discharge 1980 Previous high 1980 Previous high Site Station name record (water Mean Rank _ Mean Year Mean Rank _ Mean Year years) _ discharge discharge discharge discharge 17 - Campo Creek near Campo 1937-80 217 1 88 1941 149 1 67 1941 19 _ Tijuana River near Nestor 1937-80 _ 16,300 1 5,670 1941 9,610 1 4,250 1941 20 - Sweetwater River near 1907-27, 1,120 2 1,260 1916 618 2 1,040 1916 Descanso 1956-80 37 - Murrieta Creek at Temecula _ 1931-80 2,860 1 2,170 1969 _ 1,610 1 1,030 1969 66 _ San Jacinto River near 1917-80 5,560 1 4,490 1927 _ 3,920 1 2,360 1927 Elsinore 70 Santa Ana River below 1941-80 5,910 1 5,320 1969 4,750 1 3,580 1969 Prado Dam 84 _ Arroyo Seco near Pasadena 1914-80 549 4 1,230 1914 349 4 639 1914 97 - Sespe Creek near Fillmore 1928-80 5,090 7 - 11,500 1969 _ 2,850 8 - 7,220 1969 99 _ Santa Clara River at 1950-80 _ 14,200 3 - 25,400 1969 _ 8,340 3 13,700 1969 Montalvo 106 _ Ventura River near Ventura _ 1930-80 4,770 4 6,970 1969 _ 2,670 5 - 3,960 1969 125 - Salsipuedes Creek near 1942-80 523 3 925 1978 270 4 523 1962 Lompoc 133 Sisquoc River near Garey 1942-80 3, 440 6,250 1969 1,990 2 3,780 1969 ® no 84 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBLE 7.-Peak inflow and outflow from selected reservoirs in southern California, 1980 [Discharges provided by Big Bear Municipal Water District; County of San Diego, Department of Public Works, Flood Control Division; International Boundary and Water Commission, United States Section (for Rodriquez); and U.S. Army Corps of Engineers, Los Angeles District. >, greater than. Locations of reservoirs shown in figs. 22, 32, and 42, and on pl. 2] Inflow Outflow Date of River basin Reservoir (ft3/s) (ft3/s) - peak outflow Tijuana Barrett (1) 8,000 - February 21 Morena (1) 2,900 - February 21 Rodriquez? (1) 28,000 - January 30 Sweetwater Loveland (1) 5,000 - February 21 Sweetwater (1) 7,000 - February 21 San Diego El Capitan 40 , 000 1,080 _ February 24 San Vicente 11,500 6,000 February 21 San Dieguito Sutherland (1) 6,100 - February 21 Lake Hodges 28,000 22,000 - February 21 Santa Ana Big Bear 1,160 1,270 - February 19 Prado 342,200 7,440 _ February 21 San Gabriel, Santa Fe 315,000 18,500 - February 17 Los Angeles Whittier Narrows: San Gabriel "13,800 511,000 _ February 17 Rio Hondo 618,200 23,700 - February 14 Sepulveda 362,000 15,100 February 16 Hansen 39,300 5,020 - February 17 Santa Clara Piru 6,900 422 - February 19 Ventura Casitas >9,000 643 February 21 Santa Ynez Jamison 3,150 2,020 - February 20 Gibraltar 13,800 13,600 February 16 Cachuma 20,900 17,900 February 20 Santa Maria Twitchell >4 ,000 391 June 27 (max. daily) 'No estimate made. 2In Mexico. From Evelyn (1982). "February 17. "From Joseph B. Evelyn, U.S. Army Corps of Engineers, oral ©February 16. communication, 1984. TABLES TABLE 8.-Sediment loads at selected stations in southern California during major storm periods, 1969, 1978, and 1980 water years [In tons. Sites shown on pl. 1] Santa Ana River Santa Clara River Ventura River Storm period at Santa Ana at Montalvo near Ventura (site 76) (site 99) (site 106) 1969 water year Jan. 19-29 ............... 1,172,793 22,154,200 3,650,975 Feb. 5-8 282,200 1,482,302 68,910 Feb. 18-27 ............... 5,994,780 25,941,870 2,864,371 Total __ ................ 7,449,773 49,578,372 6,584,256 Percent of yearly total .. 64.3 98.2 98.9 1978 water year Dec. 25-29 ............... 9,165 55,384 536 Jan. 14-19 ............... 40 , 640 588,190 94,763 Feb. 5-15 ............... 579,480 9,738,297 2,084 , 444 Mar. 1-6 ..... a a e e e e e e e ee 897,400 17,651,000 1,297,320 Total ___ ................ 1,526,685 28,032,871 3,477,063 Percent of yearly total .. 68.2 95.9 98.9 1980 water year Jan. 9-19 ............ » » +. 60,285 144,695 1,254 Jan. 28-Feb.1 ............ 152,530 237,262 266 Feb. 14-24 ..... a a e e e e e e e 1,247,100 8,279,900 1,743,198 Mar. 2-7 .............}.... 550,000 769,500 13,990 Total ___ ................ 2,009,915 9,431,357 1,758,708 Percent of yearly total .. 76.2 96.1 99.7 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 9. -Annual sediment loads at selected stations in southern California for 1969-80 water years [In tons. Sites shown on pl. 1. --, data not available] Santa Ana River Santa Clara River Ventura River Water year at Santa Ana at Montalvo near Ventura (site 76) (site 99) (site 106) 1969. kk}... 11,585,094 50,490,604 6,658,137 1970. sss ss e..} 22,470 664,220 32,768 1971 ...s ks kvs s kerk sissies 17,066 2,411,145 37,263 1972. ske} }.} -- 476,051 7,094 1973... esses... 43,751 4,312,720 491 , 242 1974. 74,824 493 , 457 -- 1975. 27,224 536,080 35,703 1976. sss. .}. 6,934 67,601 1,605 1977 ..... .... .sk ses ese 5,026 61,879 956 1978. es ese .}} 2,238,835 29,218,506 3,514,054 1979. sre nea ves 71,955 2,258,110 36,714 1980. .........sks kk kkk ls 2,636,012 9,810 , 441 1,764,103 Total ............ 16,729,191 100,800,814 12,579,639 1969 as percent of total...... 69 50 53 1978 as percent of total..... 13 29 28 1980 as percent of total..... 16 10 14 Sum of 1969, 1978, and 1980 storm periods (from table 8) as percent of the 12-year total.. 66 86 94 TABLES TaBuE 10.-Gage height, in feet, and discharge, in cubic feet per second, February 14-22, 1980, at gaging station 09498500, Salt River near Roosevelt, Ariz. (site 11, pl. 2) 87 Hour hiigfil Discharge | Hour Agigft Discharge | Hour Agigft Discharge Feb. 14 Feb. 16 Feb. 19--Con. 0700 7.9 697 0100 26.7 87,400 1100 13.4 11,300 1000 8.1 841 0200 25.2 74,900 1400 13.7 12,500 1200 8.2 916 0300 24.8 71,800 1500 13.6 12,200 1400 8.7 1,370 0400 25.1 74,100 2300 14.2 14,300 1800 12.9 9,250 1200 20.2 40,800 2400 14.7 15,800 2200 16.7 20,600 2400 15.2 17,500 Feb. 20 2400 17.8 28,300 0300 17.4 26,500 Feb. 17 0600 21.1 46,100 Feb. 15 0600 14.2 12,500 1000 20.3 41,200 0400 18.9 33,700 0700 14.4 13,100 1400 20.9 45,000 1000 22.4 54,400 0800 14.1 12,200 2400 18.1 29,500 1100 22.6 55,800 2100 13.9 11,600 Feb. 21 1300 22.6 55,800 2400 14.0 11,900 0900 17.2 25,600 1700 26.1 82,300 1000 18.8 33,100 1800 25.4 76,500 Feb. 18 1100 16.5 22,500 1900 27.2 91,800 2200 12.8 8,610 2200 15.0 16,800 1930 28.0 99,000 2400 13.1 9,450 2400 15.3 17,800 2000 27.2 91,800 2100 26.7 87,400 Feb. 19 Feb. 22 2200 27.1 90,900 0200 13.8 12,800 0100 15.5 18,500 2400 26.1 82,300 0300 14.1 13,700 2400 13.5 11,600 88 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBLE 11.-Gage height, in feet, and discharge, in cubic feet per second, February 14-22, 1980, at gaging station 09499000, Tonto Creek above Gun Creek, near Roosevelt, Ariz. (site 14, pl. 2) Hour hcéiggst Discharge | Hour hailsrst Discharge| Hour h2?§:‘t Discharge Feb. 14 Feb. 16--Con. Feb. 19--Con. 0400 3.73 216 0400 7.50 7,430 1700 7.10 5,980 0600 4.00 357 0800 6.65 4,450 2000 9.50 - 15,600 0800 6.00 3,020 1600 5.80 2,610 2200 12.00 _ 27,200 1100 7.00 5,390 2400 5.55 2,160 |Feb. 20 1400 10.00 - 17,800 |Feb. 17 0030 16.50 - 57,200 1800 13.00 _ 32,200 1200 5.65 2,330 0400 10.00 _ 17,400 2300 11.30 - 23,900 2400 5.50 2,070 0600 9.80 - 16,400 2400 12.00 - 27,200 |Feb. 18 1200 8.50 - 11,000 Feb. 15 0900 5.25 1,600 2400 7.90 8,800 0500 10.70 _ 21,400 1300 5.30 1,680 |Feb. 21 0800 12.20 _ 28,300 1600 6.00 3,120 0500 7.00 5,680 0900 12.20 - 28,300 1800 8.00 8,980 1200 8.80 - 12,100 1200 14.90 _ 45,300 1930 9.00 _ 13,400 1400 8.00 9,330 1500 17.00 _ 61,400 1400 7.40 7,090 1700 10.00 _ 17,800 1800 14.00 _ 38,100 |Feb. 19 1400 8.80 - 12,100 2200 10.00 _ 17,800 0900 6.00 3,120 |Feb. 22 2400 9.00 _ 13,400 1400 6.80 5,110 1100 7.20 5,680 Feb. 16 1500 6.60 4,450 1800 6.60 4,450 0300 7.10 5,980 1600 7.50 7,430 2400 6.50 4,140 TABLES 12. -Gaged inflow to Roosevelt Lake and outflow from Stewart Mountain Dam, Ariz., for periods when the 7-day gaged inflow exceeded 200,000 acre-feet, 1913-80 [Flow in thousands of acre-feet. Total 7-day inflows generally are 5 to 10 percent greater than gaged inflows. In March 1978, January 1979, and February 1980, total inflows were 18, 39, and 35 percent, respectively, greater than gaged inflow. Total inflow not available prior to 1941. Outflow not available prior to 1937. Locations shown on pl. 2] Gaged inflow to Outflow from Stewart Flood period Roosevelt Lake Mountain Dam Highest consecutive days Highest consecutive days 1 3 7 1 3 7 January 30- 96 159 224 -- -~ -- February 5, 1915 January 16-22, 1916 212 502 693 -- -- -- January 25-31, 1916 155 302 383 -- -- -- March 23-29, 1916 57 129 206 -- -- -- December 5-11, 1919 118 201 241 -- -- -- February 21-27, 1920 131 292 394 -- -- a December 27, 1923- 104 191 285 -- -- -- January 2, 1924 February 15-21, 1927 81 216 280 -- -- -- February 9-15, 1932 84 212 290 -- e -- February 7-13, 1937 97 190 210 0.05 0.1 0.2 March 13-19, 1941 152 328 404 . 06 . 08 . 2 January 14-20, 1952 116 246 350 0 0 0 December 25-31, 1959 103 188 207 . 2 & 4 . 5 December 22-28, 1965 111 196 229 7 19 26 December 30, 1965- 80 171 207 77 171 1240 January 5, 1966 October 19-25, 1972 122 237 275 29 50 53 February 28- 216 514 658 32 53 56 March 6, 1978 December 18-24, 1978 152 345 397 75 271 1408 January 17-23, 1979 95 190 228 1107 1291 24133 February 14-20, 1980 184 316 550 127 1326 1620 'iExceeds measured inflow but is less than total inflow. Exceeds total inflow because reservoirs were being drawn down to allow for additional runoff. 89 90 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TABLE 13.-Gage height, in feet, and discharge, in cubic feet per second, February 13-22, 1980, at gaging station 09508500, Verde River below Tangle Creek, above Horseshoe Dam, Ariz. (site 37, pl. 2) Hour hiiagfit Discharge| Hour hifghet Discharge | Hour hcefggrft Discharge Feb. 13 Feb. 16 Feb. 19--Con. 2400 4.07 547 0200 17.45 44,600 2300 17.77 47,700 Feb. 14 0400 16.98 - 40,300 2400 18.62 - 56,600 0400 4,23 612 0600 16.52 36,400 Feb. 20 0700 4,78 846 0800 15.94 32,000 0100 18.91 60,000 1000 6.81 2,170 1000 15.40 28,200 0200 18.21 53,200 1200 9.08 4,780 1200 14.87 _ 24,800 0300 18.41 43,300 1300 10.37 7,120 1600 14.00 19,900 0400 19.03 61,400 1400 11.18 9,070 2000 13.44 _ 17,100 0500 19.28 - 64,400 1500 11.72 10,560 2400 12.86 14,500 0600 19.39 65,800 1700 13.10 _ 15,600 | Feb. 17 0700 19.20 - 63,400 1900 14.02 - 20,000 0500 12.46 _ 13,000 0800 19.12 _ 62,500 2000 14.14 20,580 0700 12.46 13,000 0900 19.26 64,200 2100 13.96 - 19,700 0900 12.62 - 13,600 1000 19.35 - 65,300 2300 13.07 _ 15,400 1100 12.62 - 13,600 1100 19.08 - 62,000 2400 12.81 14300 1400 12.52 13,200 1200 18.64 _ 56,900 1900 12.92 14,800 1400 18.16 51,600 Feb. 15 2400 12.63 _ 13,600 1600 17.33 - 43,500 0100 12.67 13,800 1800 16.65 37,500 0200 12.71 13,900 |Feb. 18 2000 16.48 _ 36,100 0300 13.27 16,300 0800 12.24 12,200 2100 16.59 37,000 0500 15.04 _ 25,800 1200 12.32 - 12,500 2300 16.48 - 36,100 0700 17.48 44,900 1600 12.16 12,000 1400 16.33 34,900 0900 19.22 - 63,700 1800 12.39 12,800 |Feb. 21 1100 20.34 _ 78,500 2100 13.29 - 16,400 0400 15.25 - 27,200 1300 21.04 _ 88,900 2400 14.43 _ 22,200 0700 14.73 _ 23,900 1400 21.21 91,600 1600 14.97 _ 25,400 1530 21.41 94,800 | Feb. 19 2000 14.69 _ 23,700 1700 21.08 - 89,600 0500 14.99 _ 25,500 2400 14.67 _ 23,600 1800 20.81 85,400 0900 14,70 23,700 Feb. 22 2000 19.82 71,300 1500 13.69 18,300 0400 14.66 23,500 2200 18.36 - 53,800 1800 13.66 _ 18,100 0800 14.78 _ 24,200 2300 18.39 54,100 1900 13.85 19,100 1600 13.84 19,000 2400 18.06 _ 50,600 2100 16.10 _ 33,200 2400 13.29 - 16,400 TABLES 91 TaBuE 14. -Gage height, in feet, and discharge, in cubic feet per second, February 13-25, 1980, at gaging station 09502000, Salt River below Stewart Mountain Dam, Ariz. (site 17, pl. 2) [Outflow from Salt River reservoir system] Hour hgiagfit Discharge| Hour £133; Discharge| Hour hazaggfit Discharge Feb. 13 Feb. 16--Con. Feb. 22 1000 3.34 938 2400 22.9 62,000 0200 20.5 48,600 1600 3.35 947 |Feb. 17 1500 20.0 46,000 1800 4.01 1,620 0600 22.7 60,800 2400 19.6 44,000 1900 4,2 1,880 1330 22.0 56,800 2400 4,27 1,910 1600 21.9 56,200 |Feb. 23 Feb. 14 2030 20.9 50,700 0600 9.3 42,500 1800 4,27 1,910 2400 21.3 52,900 1200 18.9 40,600 1900 4.60 2,290 |Feb. 18 1800 18.1 36,900 2000 10.85 12,600 0800 20.0 46,000 2100 17.6 34,600 2100 11.08 _ 13,200 2000 18.4 38,200 2400 17.5 34,200 2200 11.06 _ 13,100 2200 16.4 29,600 2300 10.95 _ 12,900 2300 18.0 36,400 | Feb. 24 2400 10.81 12,500 2400 17.9 36,000 0600 16.99 - 32,010 Feb. 15 Feb. 19 1200 15.79 - 27,300 0100 10.7 12,300 0800 17.3 33,300 1400 15.59 - 26,600 0200 10.9 12,700 1900 17.0 32,100 2400 15.59 - 26,600 0900 10.5 11,900 2400 17.3 33,300 |Feb. 25 1000 11.3 13,700 |Feb. 20 0500 15.39 _ 25,800 1200 18.4 38,200 0200 17.4 33,800 0900 14.59 _ 23,000 1300 20.0 46,000 1100 16.45 _ 29,800 1200 14.29 _ 22,000 1400 21.2 52,300 1600 16.8 31,200 1600 18.89 - 20,720 1500 20.9 50,700 2100 18.0 36,400 1800 9.99 10,880 1800 24.0 68,800 2400 18.5 38,700 1900 6.99 5,400 2100 25.0 75,200 1915 9.99 10,900 2400 24,4 71,200 |Feb. 21 2000 13.09 _ 18,300 Feb. 16 1200 19.6 44,000 2100 13.29 - 18,800 0700 23.2 63,800 1900 20 46,000 2300 12.99 - 18,000 1100 23.0 62,600 2400 20.4 48,000 2400 12.39 - 16,400 92 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBLE 15.-Gage height, in feet, and discharge, in cubic feet per second, February 13-25, 1980, at gaging station 09510000, Verde River below Bartlett Dam, Ariz. (site 42, pl. 2) Gage Gage Gage Hour height Discharge| Hour height Discharge| Hour height Discharge Feb. 13 Feb. 17--Con. Feb. 20--Con. 0600 2.82 780 0430 13.07 _ 24,100 1500 15.60 _ 35,100 1230 3.5 1,520 0530 11.58 - 19,000 1700 16.30 _ 38,500 1500 3.87 1,970 0830 11.47 _ 18,600 2030 16.80 _ 41,100 1715 5.1 3,950 0900 9.20 12,400 2100 14.87 _ 31,700 1815 6.25 5,800 1000 7.33 8,000 2200 14.81 _ 31,400 1915 7.40 8,090 1130 7.24 7,760 2400 14.96 _ 32,100 2145 8.5 10,600 1200 10.30 - 15,400 | Feb. 21 1230 10.68 _ 16,400 0100 15.03 _ 32,400 Feb. 14 1800 10.69 _ 16,400 0415 15.16 - 33,000 0900 8.58 10,800 1830 11.30 _ 18,200 1045 15.20 - 33,200 1815 10.25 _ 15,200 1900 11.40 _ 18,400 1515 16.50 _ 39,500 2145 10.36 _ 15,500 1930 14.30 _ 29,200 1615 17.60 _ 45,300 2400 10.39 _ 15,600 2000 14.60 _ 30,500 1845 17.60 _ 45,300 2100 14.67 - 30,800 2215 17.57 - 45,100 2400 14.52 _ 30,100 2400 17.50 _ 44,500 Feb. 15 Feb. 22 0800 10.45 _ 15,800 | Feb. 18 0430 17.15 - 42,900 0830 14.20 _ 28,800 1330 14.30 _ 29,200 0915 14.60 _ 30,500 0900 16.80 _ 41,070 1400 16.50 _ 39,500 1030 12.75 - 22,800 0930 19.40 _ 55,600 1430 19.30 _ 55,000 1200 13.15 _ 24,400 1000 20.83 _ 64,100 1530 23.00 - 78,900 1245 12.90 _ 23,400 1100 20.81 64,000 1700 21.20 - 66,500 1430 12.39 - 21,500 1200 21.92 - 71,300 1900 19.00 _ 53,200 1700 11.85 _ 19,800 1300 21.90 - 71,200 2100 17.30 - 43,700 1845 10.95 _ 17,200 1330 23.25 - 80,600 2400 15.75 _ 35,800 2000 9.00 _ 11,900 1500 22.90 - 78,100 2115 8.75 11,300 1530 24.50 - 89,900 |Feb. 19 2300 7.07 7,420 1600 24.88 - 92,900 0100 15.30 - 33,700 | Feb. 23 1700 24.95 - 93,400 0300 14.70 _ 31,000 0300 7.10 7,460 1830 25.40 - 97,300 0500 14.38 - 29,500 0800 7.87 7,130 2030 25.36 - 96,600 0830 14.30 _ 29,200 1100 8.30 - 10,100 2230 25.09 - 94,500 1130 14.43 _ 29,800 1600 9.12 - 12,200 2400 24.10 - 86,900 1545 14.34 _ 29,400 2100 9.78 - 13,900 2100 14.29 _ 29,100 2300 10.88 _ 17,100 Feb. 16 2315 14.65 _ 30,700 0030 23.80 - 84,700 2400 14.83 _ 31,500 |Feb. 24 0430 23.40 - 81,700 0500 10.74 _ 16,700 1100 22.80 - 77,400 |Feb. 20 1300 10.93 _ 17,300 1200 22.00 - 71,900 0330 16.20 _ 38,000 2000 11.93 _ 20,200 1300 21.00 _ 65,200 0430 15.15 - 33,000 1400 19.00 _ 53,200 0500 15.25 - 33,500 | Feb. 25 1500 14.13 _ 28,400 0530 14.60 _ 30,500 0430 11.45 _ 18,700 1900 14.19 _ 28,700 0600 14.63 _ 30,600 0915 12.30 - 21,300 2400 14.20 _ 28,000 0630 14.25 _ 28,000 1230 12.95 - 23,800 0800 14.92 _ 31,900 1545 12.00 - 20,400 Feb. 17 1000 15.20 - 33,200 1630 8.50 - 10,630 0200 13.94 _ 27,600 1230 15.03 - 32,400 1715 6.15 5,590 0230 13.13 _ 24,300 1400 16.40 _ 39,000 2045 6.12 5,530 TABLES TaBLE 16. -Gage height, in feet, and discharge, in cubic feet per second, February 14-24, 1980, at gaging station 09512170, Salt River at Jointhead Dam, at Phoenix, Ariz. (site 45, pl. 2) [For 2400 February 20 to 2400 February 24, stage-discharge relation is undefined. Discharge values given for that period are estimated from summation of Salt River below Stewart Mountain Dam and Verde River below Bartlett Dam and shape of recorder trace at Jointhead Dam. --, data not available] Hour hce?ggr?t Discharge Hour £533; Discharge| Hour [Exist Discharge Feb. 14 Feb. 16--Con. Feb. 20--Con. 0700 -- 0 2400 6.30 - 90,000 1200 5.01 63,000 0800 2.75 5,000 Feb. 17 1700 5.10 - 65,000 0900 3.07 6,600 0300 6.46 _ 92,000 2400 5.77 - 72,000 1000 3.13 6,940 0600 6.56 - 94,000 | Feb. 21 1400 3.26 8,000 1400 5.75 - 78,000 0200 5.92 - 76,000 1800 3.33 8,580 1700 5.00 - 63,000 0500 5.75 _ 72,000 2000 3. 40 9,200 2000 5.28 - 69,000 1500 6.17 _ 75,000 2300 3.70 - 12,000 2300 5.08 - 65,000 1900 6.25 76,000 2400 4.20 - 17,300 2400 5.15 _ 66,000 2100 6.45 _ 85,000 Feb. 15 Feb. 18 2400 6.95 _ 95,000 0200 -- 24,000 0200 6.00 - 83,000 | Feb. 22 0400 4.84 _ 25,800 0400 6.17 - 87,000 0200 7.36 100,000 0900 4.78 - 25,000 0800 6.05 _ 84,000 0800 7.20 - 97,000 1400 4.87 - 26,200 1700 5.50 - 73,000 1400 6.93 - 92,000 1500 5.50 - 35,900 2000 6.60 _ 95,000 1800 5.95 - 75,000 1600 7.00 - 63,100 2200 7.60 115,000 2400 5.42 - 67,000 1800 9.50 113,100 2400 7.00 103,000 |Feb. 23 2000 10.60 144,000 |Feb. 19 0400 4.85 - 58,000 2200 11.15 160,000 0600 5.50 - 73,000 0600 4.50 - 54,000 2400 11.3 _ 165,000 0900 5.10 - 65,000 1000 4.17 - 49,000 Feb. 16 1200 4.98 - 63,200 1400 4.03 _ 49,000 0100 11.45 170,000 1400 4.97 _ 63,000 1600 4.02 _ 50,000 0400 10.75 148,000 2000 5.27 - 69,000 2200 4.12 - 52,000 0800 9.30 135,000 2400 5.13 - 66,000 2400 4.12 - 52,000 1400 9.30 135,000 |Feb. 20 Feb. 24 1600 9.10 129,000 0200 5.30 - 69,000 0400 4.02 _ 50,000 1800 8.90 123,000 0400 5.75 - 78,000 1200 4.09 _ 52,000 2200 6.30 - 90,000 0700 5.75 _ 74,000 2100 3.77 - 46,000 2300 6.20 - 87,000 0800 5.58 75,000 2400 3.83 - 47,000 94 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 17.-Gage height, in feet, and discharge, in cubic feet per second, February 15-23, 1980, at gaging station 09519500, Gila River below Gillespie Dam, Ariz. (site 62, pl. 2) Hour hag—(met Discharge| Hour h2?gg:t Discharge| Hour hgfggfit Discharge Feb. 15 Feb. 18--Con. Feb. 21--Con. 0000 10.20 332 1100 15.10 _ 73,700 0800 15.71 91,300 0400 10.20 332 1400 15.23 79,700 1000 15.75 92,300 0800 10.41 1,050 1800 15.45 _ 85,000 1200 15.70 91,000 1200 11.07 4,820 2000 15.51 86,400 1400 15.73 91,800 1600 12.04 14,900 2200 15.51 86,400 1600 15.66 90,000 2000 12.54 _ 21,900 2400 15.49 89,900 2000 15.70 _ 91,000 2400 13.00 _ 29,300 Feb. 19 2400 15.88 95,500 Feb. 16 0400 15.31 81,600 0400 13.56 _ 39,200 0800 15.49 _ 85,900 |Feb. 22 0600 13.96 47,100 1230 16.12 102,000 0400 16.08 100,500 0800 14.71 63,000 1400 16.11 101,000 0800 16.28 105,700 1000 16.08 95,400 1600 15.95 97,200 1200 16.55 113,000 1200 17.32 134,000 2000 15.45 _ 85,000 1445 16.72 117,000 1300 17.86 149,000 1400 15.18 _ 78,600 1600 16.63 115,000 1500 18.38 165,000 | Feb. 20 2000 16.58 114,000 1830 18.81 178,000 0400 15.09 76,500 2400 16.36 108,000 2400 18.36 164,000 0800 15.31 81,600 Feb. 17 1200 16.08 100,000 |Feb. 23 0600 17.92 151,000 1600 16.78 119,000 0400 15.89 - 95,700 1200 16.72 117,000 1800 17.05 126,000 0800 15.48 _ 85,700 1600 16.16 103,000 2000 16.85 121,000 1200 15.11 _ 76,900 2400 15.74 _ 92,000 2400 16.33 107,000 1600 14.74 _ 68,500 Feb. 18 Feb. 21 2000 14.54 _ 64,100 0600 15.34 _ 82,300 0400 15.94 _ 97,000 2400 14.47 _ 62,600 TABLES 95 TaBLE® 18.-Gage height, in feet, and discharge, in cubic feet per second, February 13-21, 1980, at gaging station 09512500, Agua Fria River near Mayer, Ariz. (site 47, pl. 2) Gage Gage Gage Hour height Discharge] Hour height Discharge| Hour height Discharge Feb. 13 Feb. 15--Con. Feb. 19--Con. 2400 3.23 16.3 0400 9.27 9,580 2230 15.56 - 32,200 Feb. 14 0700 7.90 6,310 2300 14.96 _ 29,500 0330 3.30 24.3 1000 8.80 8,390 2400 13.41 _ 23,100 0400 3. 68 111 1100 9.19 9,370 | Feb. 20 0430 3.70 118 1300 8.55 7,780 0130 13.61 23,900 0600 3.95 239 1430 9.17 9,320 0200 12.66 _ 20,300 0630 4.60 830 1600 9.00 8,880 0300 10.80 _ 14,000 0730 5.20 1,620 1800 8.00 6,530 0500 8.60 7,900 0900 6.18 3,110 2100 6.65 3,880 0730 9.86 11,200 1000 6. 40 3, 460 2400 5.87 2,630 1000 7.66 5,800 1130 7.70 5,890 | Feb. 16 1300 6.72 4,000 1230 7.82 6 , 140 0600 5.03 1,380 1500 6.29 3,280 1330 8.13 6,810 1200 4.51 728 1800 5.93 2,720 1600 7.68 5,840 1800 4.19 414 2000 5.77 2 , 480 1700 10.00 11,600 2400 4.02 285 2400 5.30 1,760 1730 10.00 11,600 Feb. 19 Feb. 21 1830 10.79 _ 13,900 1300 3.40 41 0530 4.93 1,240 2000 10.10 11,800 1830 4.91 1,220 0700 5.48 2,030 2030 10.10 _ 11,800 1900 6.10 2,990 0930 6.48 3,590 2200 8.80 8,380 1930 7. 40 5 , 270 1030 6.55 3,710 2300 8.95 8,750 2000 10.20 _ 12,140 1300 6.36 3,400 2400 8.80 8,380 2030 12.26 - 18,300 1700 6.49 3,610 Feb. 15 2100 13.98 _ 25,400 2100 5.82 2,550 0130 8.6 7,900 2130 15.36 31,300 2300 5.80 2,520 0230 9.15 9,270 2200 15.76 33,100 2400 5.65 2,290 96 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBur 19.-Gage height, in feet, and discharge, in cubic feet per second, February 14-22, 1980, at gaging station 09512800, Agua Fria River near Rock Springs, Ariz. (site 49, pl. 2) [Gage height: Recorded gage height by manometer; large amounts of drawdown at high stages. Peak outside stages are 19.79 ft February 15 and 28.15 ft February 19] Hour h2?§f$t Discharge| Hour £235; Discharge| Hour hiiqgfit Discharge Feb. 14 Feb. 16 Feb. 19--Con. 0000 7.62 628 0400 12.0 4,970 2400 21.08 - 59,500 0300 7.79 698 1100 10.81 3,640 Feb. 20 0700 11.19 3,190 1900 10.15 2,950 0200 20.12 _ 27,800 0930 11.99 4,150 2400 9.84 2,630 0300 19.82 - 25,000 1200 14.66 8,360 | Feb. 17 0600 19.71 24,300 1500 17.76 _ 15,700 0400 10.16 2,780 0900 20.01 26,800 1530 18.88 19,800 0800 11.42 4,500 1200 18.55 _ 18,400 1730 16.66 - 12,700 1145 12.21 5,210 1500 16.35 12,000 2000 18.01 16,400 1800 10.84 3,550 1800 15.04 9,000 2130 17.01 13,600 | Feb. 18 2400 13.45 6,040 2400 16.27 - 11,800 0100 10.11 2,920 Feb. 15 0600 9.80 2,600 Feb. 21 0100 16.66 12,700 1200 9.85 2,650 0400 12.80 5,030 0330 16.36 - 12,000 1300 10.08 2,890 0800 14.57 8,060 0430 17.16 _ 14,000 1800 10.85 3,680 1200 15.54 _ 10,100 0630 19.18 - 21,100 1945 11.70 4,620 1600 15.83 10,800 0830 18.48 _ 18,100 2100 11.42 4,280 2000 14.88 8,670 0930 18.70 - 19,000 2400 11.04 3,890 2400 14.48 7,890 1030 19.38 - 22,200 Feb. 19 1230 19.44 _ 22,600 0400 10.66 3,500 Feb. 22 1400 18.64 _ 18,700 1400 10.48 3,320 0600 13.37 5,910 1800 16.26 - 11,800 1900 12.01 4,970 1200 12.61 4,760 2100 14.34 8,230 2000 14.99 9,300 1800 11.76 3,640 2400 13.12 6,390 2200 20.54 _ 36,800 2400 11.42 3,220 TABLES TaBue 20.-Inflow and outflow, in cubic feet per second, February 14-22, 1980, Lake Pleasant, Agua Fria River at Waddell Dam, Ariz. (sites 51A and 51B, pl. 2) [Furnished by Maricopa County Municipal Water Conservation District no. 1. --, data not available] Hour Inflow _ Outflow Hour Inflow _ Outflow Hour Inflow _ Outflow Feb. 14 Feb. 15--Con. Feb. 20--Con. 0200 697 1,550 2400 18,000 18,000 1400 25 , 400 28,800 0600 1,550 1,550 1600 -- 14,400 0800 3,730 1,550 | Feb. 16 1800 16,100 14,400 1000 5,280 3,100 0200 -- 14,400 2000 14,800 14,400 1200 12,400 9,600 0400 -- 14,400 2200 -- 9,000 1400 20,500 15,600 0500 12,900 14,400 2400 -- 9,000 1600 27,700 23,400 0700 9,950 10,800 1800 25,200 25,200 0800 5,850 5,000 | Feb. 21 2000 26,100 25,200 1000 7,620 0 0200 -- 9,000 2200 25,200 25,200 1200 -- 2,950 0330 11,500 9,000 2400 23,900 25,200 -- (1) (1) 0600 -- 9,000 Feb. 19 0800 16,000 9,000 1600 - 7,200 1000 17,000 14,400 Feb. 15 1800 9,320 14,400 1200 16,300 18,000 0400 20,300 25,200 2000 e 25,200 1400 18,000 18,000 0600 21,100 25,200 2200 41,500 44,000 1600 -- 18,000 0800 24,300 25,200 2400 59,600 52,000 1800 17,600 18,000 1000 41,400 44,000 | Feb. 20 2000 16,300 18,000 1130 42,300 44,000 0100 73,300 -- 2400 -- 18,000 1400 36,200 44,000 0200 71,700 66,600 | Feb. 22 1600 33,500 -_ 40,000 0400 58,100 66,600 0400 -- 18,000 1700 30,600 40,000 0600 43,700 46,200 0600 -- 14,400 1800 33,200 40,000 0800 37,700 36,000 0800 8,470 14,400 2000 17,500 25,200 1000 -- 28,800 1000 8,890 7,200 2200 20,500 18,000 1200 31,300 28,800 1200 8 , 470 7,200 'From 1200 February 16 to 1500 February 19, inflow ranged from 3,920 to 11,600 and outflow ranged from 1,800 to 10,600 ft}/s. See figure 52. 97 98 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TABLE 21.-Gage height, in feet, and discharge, in cubic feet per second, February 14-22, 1980, at gaging station 09513970, Agua Fria River at Avondale, Ariz. (site 57, pl. 2) Hour h2?ggfit Discharge | Hour hailgfit Discharge | Hour hcéiggfit Discharge Feb. 14 Feb. 16--Con. Feb. 19--Con. 0000 0.32 0 0700 2.38 7,100 2400 0.65 380 2100 . 32 0 0800 2.46 7,600 |Feb. 20 2200 4.50 19,500 0900 2.48 7,700 0200 1.90 4,520 2330 5.09 _ 23,500 1000 2.20 6,100 0400 3.00 - 11,400 2400 5.00 - 23,000 1200 1.70 3,550 0600 4.85 _ 26,700 1800 1.2 1,500 0700 6.65 - 43,500 Feb. 15 2400 . 7 430 0800 6.77 - 44,200 0200 4.77 - 21,400 1000 5.20 - 32,000 0300 4.63 _ 20,500 |Feb. 17 1200 3.55 - 20,500 0400 4.31 18,500 1400 &1 150 1400 3.05 - 17,300 0500 4.60 _ 20,100 1500 1.90 4,550 1500 2.75 - 15,400 0600 4.43 _ 19,000 1600 2.33 6,800 1800 3.25 - 18,500 0800 4.07 _ 16,800 1700 2.25 6,400 2400 2.40 - 13,300 0900 3.95 _ 16,300 1800 2.38 7,100 |Feb. 21 1000 4.04 _ 16,700 1900 2.32 6,700 1400 1.80 9,800 1100 4,12 17,100 2000 2.10 5,600 1500 2.85 16,000 1200 4.02 _ 16,600 2200 1.60 3,100 1900 2.60 - 14,500 1400 4.35 - 18,600 2400 1.57 2,950 2400 2.95 16,700 1600 5.62 - 27,300 Feb. 22 1800 6.15 31,000 Feb. 18 0300 3.10 17,600 2000 5.60 - 27,000 0800 1.68 3 , 450 0600 2.65 - 14,800 2200 4,45 19,300 1200 1. 40 2,210 0800 2.55 14,200 2400 3.50 - 13,500 1800 . 95 840 1000 2.28 - 12,600 2400 . 70 430 1200 2.25 12 , 400 Feb. 16 Feb. 19 1400 2.13 - 11,700 0200 2.80 9,400 0200 1.64 3,240 1600 1.38 7,500 0400 2.40 7,200 0500 1.74 3,700 1800 1.25 6,700 0500 2. 42 7,300 0700 1.67 3,400 2000 1.25 6,700 0600 2.35 6,900 1200 1.17 1,400 2400 1.18 6,400 TABLES Taste 22.-Summary of flood damage in the Phoenix, Ariz., area, February 1980 [Modified from U.S. Army Corps of Engineers, 19812] Damage, in dollars Type of damage Salt Gila Agua Fria Total River River River Residential . . . . . . 873,000 769,000 248,000 1,890,000 Commercial . . . . . . 2,806,000 284,000 31,000 3,121,000 Industrial: Sand and gravel . . 1,710,000 23,000 62,000 1,795,000 Other. . . . . . . . 1,012,000 0 0 1,012,000 Public: Roads and brldges R 16,399,000 1,360,000 4,242,000 22,001,000 Other. . . . 20. 11,639,000 619,000 1,053,000 13,311,000 Agricultural: Soil restoration . . . 33,000 1,925,000 195,000 2,153,000 Income losses. . . . -- 75,000 195,000 270,000 Other. . . . . . 108,000 1,361,000 1,113,000 2,582,000 Business and mcome Losses . . . . . . . 5,282,000 11,000 239,000 5,532,000 Emergency costs: Public . . . . . . . 615,000 8,000 2,000 625,000 Other. . . . 694,000 64,000 231,000 989,000 Transportation delays 1 Additional driver time. . . R 6,500,000 -~ -- -- Additional dlstance traveled _ . . . . 1,600,000 -- -- -- Additional operatmg costs . . . . & 280,000 -- -- -- Total, transpor— tation delays . 8,380,000 -- -- 8,380,000 Grand total . . . 49,551,000 6,499,000 =7L,611,000 63,661,000 'Transportation delays were not computed for Gila and Agua Fria Rivers. 100 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA Tasue 23. -Summary of flood stages and discharges [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Salton Sea basin 1 10254050 Salt Creek Near seee eee seee seee c}} 269 2 10255700 San Felipe Creek near Julian seee esse esse es ees 89.2 3 10255800 Coyote Creek near Borrego Springs 144 4 10255810 Borrego Palm Creek near Borrego Springs .................}..}. 21.8 5 10255850 Vallecito Creek near JUIN esses eee seee ees ees 39.7 6 10255885 San Felipe Creek near WestmorIand sees ke} }} 1,693 7 10256500 Snow Creek near White Water se ees seee }s 10.8 8 10257600 Mission Creek near Desert Hot Springs ........................ 35.7 9 10257710 Chino Canyon Creek near Palm Springs ........................ 3.88 10 10258000 Tahquitz Creek near Palm Springs 16.8 11 10258500 Palm Canyon Creek near Palm Springs 93.3 12 10259000 Andreas Creek near Palm Springs ..............ssssssssses eee. 8.61 13 10259200 Deep Creek near Palm Desert sees esses esse eee} 30.6 14 10259300 Whitewater River at INGdiQ ees sees ees ees eee ces 1,073 15 10259540 Whitewater River near M@CC@ ce}. 1,495 Tijuana River basin 16 11012000 Cottonwood Creek above Tecate Creek, near Dulzura .......... 310 17 11012500 Campo Creek near CAMPO seee se eee e e eee ee eee ee ees 85.0 18 11013000 Tijuana River near DulIZzUr@...........s.s.sessss esses seee s ss esse ees 481 19 11013500 Tijuana River near ses esse eee eee e eee eee ees 1,695 See footnotes at end of table. at selected gaging stations in southern California TABLES 101 on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft] (ft/s) (years) Salton Sea basin 1961-80 1976 14.3 9,900 21 9.44 1,290 6 1958-80 1967 4.08 1,050 21 7.85 6,150 >100 1950-80 1977 =~~ 3,840 21 7.50 3,890 18 1950-80 1979 9.8 2,640 21 5.42 279 8 1963-80 1976 6.30 1,160 18 16.22 231 5 1960-80 1976 19.0 100,000 21 8.65 3,440 2 1921-31, 1969 213.8 13,000 16 5.64 1,040 4 1959-80 1967-80 1969 6.40 1,660 19 3.30 749 8 1974-80 1977 5.93 247 21 5.38 95 --- 1947-80 1965 12.34 2,900 21 --- 1,690 15 1969 1930-42, 1979 6.38 4,400 21 7.29 7,000 30 1947-80 1948-80 1954 7.11 1,960 18 4.38 411 6 1962-80 1976 7.84 7,100 21 5.08 1,170 6 1938, 1938 --- 29,000 17 4.12 6,100 7 1965-80 1960-80 1969 --- 32,500 21 --- 1 32,100 CCC Tijuana River basin "1936-80 1980 9.70 5,980 21 11.15 11,700 >100 1936-56 1937 4.80 880 20 4.36 652 14 "1957-80 1958 3.70 367 "1936-80 1980 10.20 6,780 18 11.19 ~~~ ~~~ 21 --- 112,200 100 1914-15, 1980 11.50 32,000 21 8.70 33,500 h "1936-80 102 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TasBue 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Sweetwater River basin 20 11015000 Sweetwater River near DeSC@NSO 45 . 4 San Diego River basin 21 11022500 San Diego River near SaNt@@ .............eesse sees e eee eee ee e}} 377 Los Penasquitos Creek basin 22 11023250 Poway Creek Near POW@Y sees seee esses esses ees 7.92 23 11023310 Rattlesnake Creek at POW@Y eee 8.13 24 11023325 Beeler Creek at Pomerado Road, near Poway 5.46 25 11023330 Los Penasquitos Creek below Poway Creek, near Poway ........ 31.2 26 11023340 Los Penasquitos Creek near Poway 42.1 San Dieguito River basin 27 11025500 Santa Ysabel Creek near Ramon@ 112 28 11027000 Guejito Creek near San Pasqual }}} 22.5 29 11028500 Santa Maria Creek near RaMON@ 57.6 San Luis Rey River basin 30 11031500 Agua Caliente Creek near Warner Springs ..................... 19.0 31 11033000 West Fork San Luis Rey River near Warner Springs ........... 25.5 32 11037700 Pauma Creek near Pauma Valley .......... ra 11.0 33 11040000 San Luis Rey River at Monserate Narrows, near Pala .......... 373 34 11040200 Keys Creek tributary at Valley Center 7.65 35 11042000 San Luis Rey River at Oceanside 558 See footnotes at end of table. TABLES selected gaging stations in southern California-Continued 103 on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft) (ft3/s) (years) Sweetwater River basin 1905-27, 1927 213.2 11,200 20 12.31 6,750 25 1956-80 San Diego River basin 1863-1932 1916 225.1 70,200 21 12.82 3,420 9 "1933-80 1937 29,4 14,200 Los Penasquitos Creek basin "1977-80 1978 6.15 375 21 7.26 755 --- 1970-80 1980 1.74 567 21 2.88 1,430 --- "1977-80 1980 9.20 1,410 21 9.00 1,240 --- "1970-80 1978 9.85 3,530 21 11.11 4,990 --- "1964-80 1978 --- 14,700 21 10.26 4,750 30 San Dieguito River basin 1863-1953 1916 214.0 28,400 21 14.25 10,700 27 "1954-80 1969 11.55 6,180 1946-80 1980 7.11 3,710 20 7.22 3,940 50 1885-1946 1916 14.1 7,140 21 14.39 15,200 65 "1946-80 1958 5.42 5 , 220 San Luis Rey River basin 1961-80 1966 5.18 1,200 21 4.80 1,440 40 1913-15 , 1966 --- 4,200 21 15.60 6,200 33 1956-80 1978 14.35 --- 1964-80 1980 --- 2,320 20 8.51 3,170 65 1966 8.60 eke "1935-41, 1980 9.97 12,100 21 9.68 15,500 e "1946-80 1969-80 1980 8.59 1,580 21 8.80 1,680 --- 1891-1929 1891 --- 128,000 21 14.00 25,000 =-- "1929-80 1980 15.83 21,000 104 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBur 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Santa Margarita River basin 36 11042400 Temecula Creek near Aguanga ..... sxe vec ses 131 37 11043000 Murrieta Creek at Temecula seee}. 222 38 11044000 Santa Margarita River near Temecula .................. 588 39 11044500 Santa Margarita River near Fallbrook ............. - sa sa ress ae .> 644 40 11046000 Santa Margarita River at Ysidora ......... s lase ara 740 San Juan Creek basin 41 11046550 San Juan Creek at San Juan Capistrano ....................... 117 42 11047000 Arroyo Trabuco near San Juan Capistrano ..................... 35.7 43 11047200 Oso Creek at Crown Valley Parkway, near Mission Viejo ....... 14.0 Aliso Creek basin 44 11047500 Aliso Creek at El TOFO bis ele a we've ia le le e 7.91 San Diego Creek basin 45 11048500 San Diego Creek at Sand Canyon Avenue, near Irvine ......... 40 . 5 Santa Ana River basin 46 11051500 Santa Ana River near Mentone........ ¥¥+aass sah ese sess ra a's a ess a 210 47 11054000 Mill Creek near Yucaipa .............. ras 42,4 See footnotes at end of table. TABLES 105 selected gaging stations in southern California-Continued on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft] (ft3/s) (years) Santa Margarita River basin 1957-80 1958 --- 3,540 21 12.0 3,420 27 1969 10.6 -_- "1930-80 1943 13.82 17,500 21 13.70 21,800 23 1923-47 1927 14.6 25,000 21 16.5 22,000 15 "1948-80 1969 15.32 14,600 1924-47 1927 215.6 33,100 21 14.4 21,000 12 "1948-80 1969 14.18 20,000 1923-47 1927 218.00 33,600 18 "18.80 24,000 10 "1948-80 1969 15.89 19,200 San Juan Creek basin 1928-80 1969 25.6 22,400 18 17.8 kc --- 20 -- 11,400 --- 1930-65 1937 6.80 9,240 18 3.18 3,140 12 "1966-77 1969 5. 42 8,000 1970-80 1973 57.67 16 7.60 5,150 23 1979 --~ 2,400 Aliso Creek basin 1930-80 1969 211.00 2,500 16 --- 1,870 12 18 53.82 --- San Diego Creek basin 1949-80 1969 --- 6,700 16 21.17 7,720 70 1978 18.41 --- Santa Ana River basin "1891-1980 1891 =-- 53,700 21 7.85 5,930 6 1919-80 1969 16.8 35,400 16 9.85 --~ --- 18 --- 2,480 6 106 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Santa Ana River basin--Continued 48 11055500 Plunge Creek near East Highlands ............................. 16.9 49 11055800 City Creek near Highland .......................... 19.6 50 11056500 Little San Gorgonio Creek near Beaumont ...................... 1.74 51 11057500 San Timoteo Creek near Loma Linda ........ 125 52 11058500 East Twin Creek near Arrowhead Springs ..................... 8.80 53 11058600 Waterman Canyon Creek near Arrowhead Springs .............. 4.65 54 11059000 Warm Creek Floodway at San Bernardino........... 47.8 55 11059300 Santa Ana River at E Street, near San Bernardino ............ 532 56 11060400 Warm Creek near San Bernardino .................... 15.0 57 11062000 Lytle Creek near Fontana ............ e s e e e ees 46.3 58 11063000 Cajon Creek near Keenbrook ..... 40 . 6 59 11063500 Lone Pine Creek near Keenbrook ................... rire s 15.1 60 11063680 Devil Canyon Creek near San Bernardino ........ 5.49 61 11065000 Lytle Creek at Colton ............. ssa sere ss 172 62 11066500 Santa Ana River at Riverside Narrows, near Arlington......... 855 63 11069500 San Jacinto River near San Jacinto ......... 141 64 11070050 Bautista Creek at Valle Vista .............. si sass sharers t sees +» 47.2 65 11070375 San Jacinto River at Railroad Canyon Weir, near Elsinore...... 562 66 11070500 San Jacinto River near Elsinore ...................... 723 67 11072000 Temescal Creek near Corona........... 6164 68 11073200 San Antonio Creek below San Antonio Dam............ sak 26.9 69 11073360 Chino Creek at Schaefer Avenue, near Chino ..... 48.9 70 11074000 Santa Ana River below Prado Dam ........ s sars rraasissssss 61,490 See footnotes at end of table. selected gaging stations in southern California-Continued TABLES 107 on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft) (ft3/s) (years) Santa Ana River basin--Continued 1919-80 1938 -== 5,340 16 5.65 1,200 5 1919-80 1969 9.39 7,000 16 8.44 2,790 15 1948-80 1969 8.50 5,900 16 3.46 65 3 1927-80 1969 28.2 15,000 16 8.50 3,400 27 1919-80 1980 8.35 3,710 16 5.30 919 2 1911-14, 1938 --- 2,350 16 4.41 545 2 1919-80 "1961-80 1969 6.75 9,600 16 5.65 4,510 8 "1939-80 1969 211.9 28,000 18 13.40 14,500 --- 1964-80 1978 --== 112,000 16 2.88 2,330 6 1918-80 1969 15.0 35,900 16 9.22 10,300 30 1919-80 1938 226.0 14,500 16 9.59 4,240 9 1919-38, 1938 --- 6,180 16 5.91 713 7 1949-80 1911-14, 1969 25.40 3,720 19 6.70 672 12 1919-80 "1957-80 1978 14.8 17,500 16 8.90 8,070 8 1862-1926 1862 e-- 320,000 18 10.40 19,500 --- "1927-80 1938 === 100,000 "1920-80 1927 ~~ 45,000 21 12.70 17,300 48 "1969-80 1979 3.30 1,390 21 6.40 8 , 320 >100 "1951-80 1969 === 5,330 22 7.27 5,700 34 "1916-80 1927 11.8 16,000 22 9.53 9,010 30 "1927-80 1938 --= 14,900 18 --- 3,500 k= "1962-80 1969 11.22 8 , 420 20 ~== 1470 --- "1969-80 1969 couped 79,200 16 7.07 1,260 e 1978 9.66 === d# 0 mm - "@ 00 5000 0 ra® 00 -- 108 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Santa Ana River basin--Continued 71 11075600 Santa Ana River at Imperial Highway, near Anaheim ........... 61,544 72 11075720 Carbon Creek below Carbon Canyon Dam ...................... 19.5 73 11075755 Santa Ana River at Ball Road, at Anaheim ..................... 61,587 74 11075800 Santiago Creek at 12.5 75 11077500 Santiago Creek at Santa AN@ 98.6 76 11078000 Santa Ana River at Santa 61,700 San Gabriel River basin 77 11085000 San Gabriel River below Santa Fe Dam, near Baldwin Park ..... 236 78 11087020 San Gabriel River above Whittier Narrows Dam................. 353 79 11088500 Brea Creek below Brea Dam, near Fullerton ................... 21.6 80 11089500 Fullerton Creek below Fullerton Dam, near Brea ............... 4.94 81 11090200 Fullerton Creek at Richman Avenue, at Fullerton .............. 12.1 Los Angeles River basin 82 11092450 Los Angeles River at Sepulveda Dam .......................... 158 83 11097000 Big Tujunga Creek below Hansen Dam ......................... 153 84 11098000 Arroyo Seco near Pasad@n@ 16.0 85 11101250 Rio Hondo above Whittier Narrows Dam ........................ 91.2 86 11102300 Rio Hondo below Whittier Narrows Dam ........................ 124 87 11103000 Los Angeles River at Long Beach.............................. 827 Calleguas Creek basin 88 11105850 Arroyo Simi near SIMI eee eee ece e. 70.6 89 11106400 Conejo Creek above Highway 101, near Camarillo .............. 64.2 90 11106550 Calleguas Creek at Camarillo State Hospital .................... 248 See footnotes at end of table TABLES 109 selected gaging stations in southern California-Continued on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft) (ft3/s) (years) Santa Ana River basin--Continued "1973-80 1978 --- 14,000 19 4.80 10,600 --- 1927-72 1927 --- 2,500 17 4 , 44 407 --- "1973-80 1978 4.38 394 "1976-80 1979 5.40 8,380 16 5.08 11,100 --- "1961-80 1969 10.50 6,520 18 9.03 1,810 9 "1928-80 1969 29.10 6,600 16 5.82 1,560 --- 1923-40 1938 210.20 46,300 16 9.62 --- --- "1941-80 1969 6.90 19,100 18 9.10 17,800 --- San Gabriel River basin "1942-80 1969 22.20 30,900 17 19.51 18,500 --- "1955-80 1969 10.90 46,600 17 10.70 43,800 --- "1942-80 1979 =-- 1,190 18 --- 31,700 --- "1941-80 1969 7.32 313 18 7.69 299 --- "1959-80 1980 6.70 2,050 16 6.50 1,950 25 Los Angeles River basin "1929-80 1978 12.04 14,700 16 intuind 15,100 25 "1932-80 1938 s 154,000 17 4.75 5,020 --- "1910-80 1938 9.42 8,620 16 6.06 3,080 10 "1956-80 1969 7.23 17,700 16 7.35 18,200 ke "1966-80 1969 13.82 38,800 14 10.50 23,700 kw "1928-80 1969 16.00 102,000 16 17.99 129,000 f Calleguas Creek basin 1969-80 1978 7.5 7,730 16 8.80 9,310 34 1972-80 1978 20.44 9,830 16 21.67 11,800 10 1968-80 1969 8.50 --- 16 10.54 25,300 32 1978 -- 18,700 110 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Santa Clara River basin 91 11108500 Santa Clara River at Los Angeles-Ventura County line ......... 625 92 11109250 Lockwood Creek at Gorge, near Stauffer ...................... 58.7 93 11109600 Piru Creek above Lake PIU .........ssseseseesee sees sees ees ess 372 94 11109800 Piru Creek below Santa Felicia Dam............................ 425 95 11110500 Hopper Creek near PIPU esses eee seee eee ees 23.6 96 11111500 Sespe Creek near Wheeler SpringS....................}........ 49.5 97 11113000 Sespe Creek mear FillMOF@ es eee eee}. 251 98 11113500 Santa Paula Creek near Santa Paula ........................... 40.0 99 11114000 Santa Clara River at MONt@IVO . eee seee ees 1,612 Ventura River basin 100 11115500 Matilija Creek at Matilija Hot Springs 54.6 101 11116000 North Fork Matilija Creek at Matilija Hot Springs .............. 15.6 102 11117500 San Antonio Creek at Casitas Springs ......................... 51.2 103 11117600 Coyote Creek near O@K VI@W 13.2 104 11117800 Santa Ana Creek near O@K Vi@W 9.11 105 11118000 Coyote Creek near eee esse ees 41.2 106 11118500 Ventura River near Ventura seee seee. 188 Carpenteria Creek basin 107 11119500 Carpenteria Creek near Carpenteri@ 13.1 San Ysidro Creek basin 108 11119660 San Ysidro Creek at 3.07 See footnotes at end of table TABLES 111 selected gaging stations in southern California-Continued on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft}/s) (ft) (ft3/s) (years) Santa Clara River basin "1952-80 1969 19.01 68,800 16 6.50 13,900 8 1971-80 1978 7.32 1,070 16 5.45 2,490 kene "1939-80 1938 --- 35,000 16 7.92 6,900 4 "1955-68, 1958 3.66 544 19 --- 3422 --- 1973-80 1930-80 1969 12.72 8,400 16 11.60 8,120 32 1947-80 1978 14.18 10,700 16 10.82 6,780 12 1911-80 1969 924.95 --- 16 19.53 40,700 13 1978 --- 73,000 1927-80 1969 18.18 21,000 16 12.59 11,800 14 "1927-80 1969 17.41 165,000 16 10.38 81,400 --- Ventura River basin "1927-80 1969 16.5 20,000 16 11.19 10,600 10 1928-80 1969 11.0 9,440 16 7.51 3,720 10 1949-80 1969 14.30 16,200 16 10.65 7,380 12 1958-80 1969 12.00 8,000 16 513.72 5,100 10 1938, 1969 10.70 inz 16 9.49 3,830 12 1958-80 1978 --- 5,330 1927-58 1938 --- 11,500 16 9.69 --- kene "1967-80 1978 11.63 420 21 --- 643 --- 1911-14, 1969 24.3 e 16 14.60 37,900 19 "1929-80 1978 intuited 63,600 Carpenteria Creek basin 1941-80 1971 14.10 8,880 16 8.50 2,000 8 San Ysidro Creek basin "1969, 1969 --- 5,620 16 2.85 332 e 1972-80 112 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBuE 23. -Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Sycamore Creek basin 109 11119700 Sycamore Creek at Santa Barbara 3.41 Mission Creek basin 110 11119750 Mission Creek near Mission Street, at Santa Barbara........... 8.38 Arroyo Burro Creek basin 111 11119780 Arroyo Burro Creek at Santa Barbara ..................... 6.65 Atascadero Creek basin 112 11119940 Maria Ygnacio Creek at University Drive, near Goleta ......... 6.35 113 11120000 Atascadero Creek near Goleta - 18.9 San Jose Creek basin 114 11120500 San Jose Creek near Goleta ............. 5.51 115 11120510 San Jose Creek at Goleta ..... 9.42 Carneros Creek basin 116 11120530 Tecolotito Creek near Goleta.......... + at% ss + 4, 42 Gaviota Creek basin 117 11120550 Gaviota Creek near seee eee e eee seee ees 18.8 Jalama Creek basin 118 11120600 Jalama Creek near Lompoc ........ vara 20.5 Santa Y¥nez River basin 119 11123000 Santa ¥nez River below Gibraltar Dam, near Santa Barbara.... 216 120 11123500 Santa ¥nez River below Los Laureles Canyon, near 277 Santa Ynez. See footnotes at end of table TABLES 113 selected gaging stations in southern California-Continued on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft) (ft3/s) (years) Sycamore Creek basin 1970-80 1978 4.65 1,120 16 4.83 582 --- Mission Creek basin 1970-80 1973 4.97 2,580 16 5.45 1,300 =~ Arroyo Burro Creek basin "1970-80 1978 5.67 1,850 16 5.66 1,850 --- Atascadero Creek basin 1970-80 1978 5.87 1,650 16 3.69 765 -=- 1941-80 1973 --- 5,380 16 10.27 4,600 13 1974 213.3 --- San Jose Creek basin 1941-80 1943 12.74 --- 16 7.39 1,370 9 1969 m_ 2,000 1970-80 1978 5.65 2,330 16 4, 44 1,330 --- Carneros Creek basin 1970-72 1971 3.14 397 16 4,47 1,610 5 Gaviota Creek basin 1966-80 1967 n_ 4,000 19 8.13 2,560 5 1978 9.09 mew Jalama Creek basin 1965-80 1978 11.34 4,020 16 8.36 2,480 7 Santa ¥nez River basin "1920-80 1969 25.8 54,200 16 1016.63 13,600 --- "1947-80 1969 18.88 67,500 16 11.84 17,800 sa- 114 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 23.-Summary of flood stages and discharges at [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) Santa ¥nez River basin--Continued 121 11124500 Santa Cruz Creek near Santa YN@Z 74.0 122 11128250 Alamo Pintado Creek near Solvang ........ 29.4 123 11128500 Santa ¥nez River at Solvang .................... aera sai nad s 579 124 11129800 Zaca Creek near Buellton............. va kake re ik ia kers 32.8 125 11132500 Salsipuedes Creek near Lompoc ........... 47.1 126 11133000 Santa Ynez River at Narrows, near Lompoc .................... 789 127 11134800 Miguelito Creek at Lompoc .................. s va kakes aaa se 11.6 128 11135000 Santa ¥nez River at Pine Canyon, near Lompoc............... & 844 San Antonio Creek basin 129 11135800 San Antonio Creek at Los Alamos ............. iiss irises ri sss 34.9 130 11136100 San Antonio Creek near Casmalia ...... irk ias balls Calls s 135 Santa Maria River basin 131 11136800 Cuyama River below Buckhorn Canyon, near Santa Maria ...... 886 132 11137900 Huasna River near Arroyo Grande.......... iaa kara ie a+ 103 133 11138500 Sisquoc River near Sisquoc............ 281 134 11139500 Tepusquet Creek near Sisquoc ........ saas s bie d sie s aer 64k 6 %%% 28.7 135 11140000 Sisquoc River near Garey .................... isis 471 136 11141000 Santa Maria River at Guadalupe ........... € lieve bales se brs Coble k a s 1,741 1Estimated. 2Datum then in use. Maximum daily. "Regulated. ©Backwater or tide affected. TABLES 115 selected gaging stations in southern California-Continued on pl. 1] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft) (ft3}/s) (years) Santa ¥nez River basin--Continued 1941-80 1969 14.45 7,050 16 11.15 2,620 6 1969-80 1969 10.32 see me 19 5.34 397 --- 1970-80 1978 6.80 724 "1928-80 1969 17.1 1g2,000 19 7.16 21,600 --- 1963-80 1969 --- 1,390 19 3.83 96 4 1978 9.66 --- 1941-80 1952 20.8 11,400 16 8.77 4,890 6 41947-80 1969 24.20 80,000 19 11.35 16,300 --- 1969-80 1969 5.83 680 16 6.30 787 mre "1941-80 1969 24.91 178,000 20 9.66 16,200 --- San Antonio Creek basin 1970-80 1978 9.58 1,270 19 3.42 228 --- 1955-80 1978 13.22 3,440 16 8.98 967 7 Santa Maria River basin 1929-80 1969 --- 17,800 17 9.42 ~- --- 1978 14.74 ke- 19 8.97 3,130 5 1929-80 1969 15.90 21,000 18 7.66 2,560 5 1929-80 1966 15.75 23,200 19 7.57 5,120 4 1943-80 1966 5.48 788 18 6.05 301 8 1940-80 1966 13.50 sss 19 7.80 7,980 7 1969 --- 24,500 "1940-80 1952 ««« 32,800 20 7.40 9,700 10 1969 10.00 sus 6Excludes 768 mi above Lake Elsinore. At site 6.1 mi downstream. SAt site 2.5 mi downstream. debris wave. '"Recorded gage height; gage height from flood marks is 18.5 ft. 116 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBur 24. -Summary of flood stages and dis- [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) 1 09479500 Gila River near LaVve@N a.... 220,615 2 09489000 Santa Cruz River near Laveen.............. a a a e e e e e e ees 8,581 3 09489100 Black River near Maverick ...... 315 4 09489500 Black River below pumping plant, near Point of Pines ......... 560 5 09489700 Big Bonito Creek near Fort Apache..... s ras ass ses is 119 6 09490500 Black River near Fort Apache 1,232 7 09494000 White River near Fort Apache ....... 632 8 09497500 Salt River near ChrySOtil@..........sssesees esses eee ee seee ee ces 2,849 9 09497800 Cibecue Creek near ChrySOtil@ 295 10 09497980 Cherry Creek near see eee es 200 11 09498500 Salt River near ROOSe@V@It } - 4,306 12 09498508 Upper Parker Creek near Roosevelt3 ......... 1.09 13 09498870 Rye Creek near GiSQ@IA ese eee 122 14 09499000 Tonto Creek above Gun Creek, near Roosevelt ................ 675 15 ___ _ _«eccc=_« Fish Creek above Lewis and Pranty Creek, 32.2 near Tortilla Flat. 16 09501300 Tortilla Creek at Tortilla Flat ...... 24.3 17 09502000 Salt River below Stewart Mountain Dam .......... vas sas i ¥a #s ass 6,232 18 09502800 Williamson Valley Wash near Paulden ........................... 255 19 09503700 Verde River near Paulden ........ 52,530 20 09503740 Hel! Canyon tributary near AshfOrk .75 21 09503750 Limestone Canyon near Paulden........................ 14.50 22 09503800 Volunteer Wash near Bellemont ...... s » 131 23 09504000 Verde River near Clarkdale ............. 0 ©3,520 24 09504400 Munds Canyon tributary near Sedona ....... is tik hs 1.19 See footnotes at end of table. TABLES 117 charges in the Gila River basin of Arizona on pl. 2) Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft) (ft3/s) (ft] (ft3/s) (years) 1940-80 1941 --- 11,900 23 7.49 545 1 1978 10.20 -== 1940-80 1962 17.50 9,200 20 9.36 115 1 1962-80 1972 8.99 11,100 19 3. 46 856 1 1953-80 1972 18.0 17,900 15 10.65 6,640 7 1957-80 1978 9.09 ~~~ 15 8.19 3,440 25 1978 ~~= 4,510 1912-80 1916 ~~~ 250,000 15 24.0 40,000 25 1957-80 1978 15.71 14,600 15 12.07 8,160 11 1906-80 1916 18 74,000 15 16.06 58,300 25 1959-80 1977 17.3 22,200 15 11.67 10,600 8 1965-80 1979 === 15,700 15 13.8 13,500 16 1906-80 1941 --= 117,000 15 28.0 99,000 25 1978 29.35 --- 1934-80 1945 --- 270 15 3.86 68.8 8 1963-80 1970 14.1 44,400 19 5.75 4,550 3 1940-80 1979 17.0 61,400 15 17.0 61,400 25 1978-80 1978 hes 2,650 15 e-- 2,450 8 1942-80 1971 13.23 7,500 15 9.9 4,250 4 "1930-80 1979 23.3 65,000 15 25.0 75,200 ~~~ 1965-80 1980 8.23 7,520 20 8.93 10,100 20 1963-80 1980 10.24 8,870 20 12.72 15,700 33 1964-80 1969 7.60 84 (6) 5.78 20 --- 1969-80 1971 16.51 4,100 15 5.11 500 3 1966-80 1978 6.55 2,300 (6) 5 . 42 1,150 infured 1915-21, 1920 719.1 50,600 15 17.92 30,100 -== 1965-80 1964-80 1970 11.10 705 (6) 6.61 180 ~~ 118 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBue 24. -Summary of flood stages and discharges [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) 25 09504500 Oak Creek near COFNViII@ 357 26 09504800 Oak Creek tributary near . 048 27 09505200 Wet Beaver Creek near RimrOCK * 111 28 09505250 Red Tank Draw near RiMPOCK 49,4 29 09505255 Woods Canyon near Munds Park3 .............................. 18.9 30 09505260 Bar M Canyon near Munds Park3 25.6 31 09505300 Rattlesnake Canyon near RimrOCK ......................... 24.6 32 09505350 Dry Beaver Creek near RimrOCK 142 33 09505550 Verde Creek below Camp Verde 54,670 34 09505800 West Clear Creek near Camp Verde 241 35 09507980 East Verde River near Childs ....... 328 36 09508300 Wet Bottom Creek near Childs 36.4 37 09508500 Verde River below Tangle Creek, above Horseshoe Dam........ 55,872 3G ___ _ -----~--~~- Deadman Creek near Horseshoe Dam ........................... 36.3 39 ___ _ _----_--_-- Lime Creek near Horseshoe Dam, near Carefree................ 41.9 4Q ___ _ Davenport Creek near Horseshoe Dam ......................... 25.5 41 |___ Sheep Creek near Horseshoe Dam.............................. 34.2 42 09510000 Verde River below Bartlett Dam .................... 56,185 43 09510190 East Fork Sycamore Creek near Sunflower ..................... 4,49 44 09510200 Sycamore Creek near Fort McDowell ........................... 164 45 09512170 Salt River at Jointhead Dam, at Phoenix ....................... 13,500 46 09512280 Cave Creek below Cottonwood Creek, near Cave Creek ........ 82.7 47 09512500 Agua Fria River near M@Y@r 588 See footnotes at end of table. in the Gila River basin of Arizona-Continued TABLES 119 on pl. 2] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft] (ft3/s) (ft] (ft3/s) (years) 1885-1980 1938 823 --- 20 16.30 26,400 25 1940-80 1970 16.48 --- 1978 wen 25,100 1963-80 1969 6.51 53 (6) 4.54 24 7 1961-80 1970 12.41 7,670 19 13.96 10,900 14 1957-80 1970 13.3 10,500 (6) 10.73 6,000 12 1961-80 1970 7.9 3,990 14 5.24 1,720 --- 1961-80 1970 9.35 --- 19 4.88 1,530 ~~ 1978 --- 4,210 1957-80 1970 11.50 3,590 14 11.90 4,000 --- 1960-80 1970 14.35 26,600 14 12.53 18,600 9 1970-80 1978 21.27 55,000 15 19.30 50,900 6 1964-80 1978 11.6 22,400 19 10.42 15,100 7 1961-80 1970 20.5 23,500 20 15.10 14,100 7 1967-80 1978 15.72 6,680 19 16 6,830 11 1924-80 1938 19.0 100,000 15 21.41 94,800 20 1978-80 1978 --- 6,620 (6) --- 3,220 12 1978-80 1978 --- 5,180 (8) --- 7,860 33 1978-80 1978 --- 5,500 (6) --- 2,670 9 1978-80 1978 --- 6,660 (6) --- 2,640 8 1888-1939 1891 --- 9150,000 15 25.4 97,300 --- "1939-80 1978 25.9 101,000 1959-80 1970 9.50 1,940 19 4.82 300 6 1959-80 1970 19.7 24,200 15 11.42 10,400 6 1871-1938 1891 --- 300,000 16 2911.45 170,000 kenn "1939-80 1978 --- 126,000 1980 --- --- --- 19 9.5 7,020 --- 1940-80 1970 14.90 --- 19 15.76 33,100 >100 1978 --- +926 120 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA 24. -Summary of flood stages and discharges [Sites shown Permanent Drainage Site station Stream and place of determination area number (mi?) 48 09512600 Turkey Creek near CI@tOP ees ee 89.4 49 09512700 Agua Fria River tributary No. 2 near Rock Springs ........... 1.11 50 09512800 Agua Fria River near Rock Springs ........................... 1,130 51A 09513000 Agua Fria River at (above) Waddell Dam....................... 1,459 51B 09513000 Agua Fria River at (below) Waddell Dam ....................... 1,459 52 09513650 Agua Fria River at El Mirage 1,637 53 09513780 New River near Rock SPriNGS 67.3 54 09513800 New River at NeW RIVET esse eee ese eee eee els 83.3 55 09513835 New River at Bell Road, near Peoria .......................... 187 56 09513860 Skunk Creek mear PhO@NIX ............sssssesesesssseeeceeeces 64.6 57 09513970 Agua Fria River at Avondale 2,018 58 09515000 Hassayampa River at Walnut Grove, near Wagoner ............. 90.9 59 09515500 Hassayampa River at Box damsite, near Wickenburg ........... 417 60 09516500 Hassayampa River near MorristOWNn 774 61 09517000 Hassayampa River near ArlingtOM 1,470 62 09519500 Gila River below Gillespie el.}. 49,650 63 09519800 Gila River below Painted Rock Dam ............................ 50,910 64 09520360 Gila River near MON@WK esse eee eee eee eee e ees 55,430 65 09520500 Gila River near DOM@................ssssssese sess ese eee ee ees 57,850 66 09520700 Gila River near mouth, near Yuma......... 59,950 "Of which 7,729 mi" is downstream from Coolidge Dam. @Estimated on basis of records for Salt River near Chrysotile. 3Part of a U.S. Forest Service small watershed project. Several nearby stations are not included. "Regulated. Includes 373 mi in Aubrey Valley Playa, a closed basin. ©Date unknown. TABLES k 121 in the Gila River basin of Arizona-Continued on pl. 2] Maximum prior to February 1980 Maximum in February 1980 Period Gage Gage Recurrence Year height Discharge Day height Discharge interval (ft] (ft3/s) (ft] (ft3/s) (years) 1970-80 1970 16.0 9,000 19 11.51 5,230 -== 1963-80 1964 19.54 1,200 (6) 6.32 405 4 1970-80 1978 27.2 52,800 19 28.15 59,500 --» 1891-1980 1919 733.0 ©105,000 20 --= 73,300 --- "1927-80 1978 --- 59,500 20 --- 66,600 --- "1963-80 1978 11.70 58,400 20 10.14 41,800 --- 1960-80 1970 13.5 18,600 19 8.13 9,350 6 1960-80 1970 9.98 19,500 19 11.44 14,900 10 1960-80 1967 13.5 14,600 20 8.91 21,100 8 1959-80 1964 --- 11,500 20 7.60 1,210 3 1970 12.24 --- "1959-80 1970 11.21 ~~~ 20 6.77 44,200 infuried 1978 6.08 29,200 1980 --= --= --- 19 5.08 3,760 --- 1891-1978 1970 34.6 58,000 19 18.9 24,900 25 1916-80 1970 19.0 47,500 20 14.32 17,000 10 1961-80 1970 8 . 40 39,000 20 2.76 11,000 7 1891-1920 1891 - 250,000 17 18.81 178,000 --- 1921-80 1978 17.06 125,000 "1959-80 1979 10.57 3,340 (11) 10.02 5,060 --- "1966-80 1979 11.12 3,080 (11) 12.0 --- --- (11) --- 4,070 1903-58 1916 --- '2200,000 (11) 6.94 4,080 --- "1959-80 1979 12.17 3,330 "1975-80 1979 --- 2,580 (11) --- --- Site and datum then in use. 8Upstream from bridge; gage is on downstream side of bridge. Estimated on basis of records for Salt River above and below Verde River. iO Revised. 'lAfter February. 2Maximum daily. 122 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBLE 25. -Known aerial photographic coverage of southern California available from government agencies for the floods of January and February 1980 Area of photography Date Coachella Valley Water District, Coachella, California Whitewater River from Salton Sea to Feb. 24 and Windy Point; approximately 55 miles Feb. 25, 1980 International Boundary and Water Commission, United States and Mexico, United States Section, El Paso, Texas Tijuana River from international Jan. 31, 1980 boundary to the Pacific Ocean Mar. 20, 1980 Los Angeles County Flood Control District, Los Angeles, California Van Tassel Canyon Feb. 20, 1980 Santa Anita Canyon-Wilderness Park Do. Lannan debris basin and debris disposal area Do. Sturtevant debris basin Do. Sierra Madre Dam Do. Carter debris basin and Carter Crib Dam Do. Auburn debris basin and Floral debris basin Do. Bailey debris basin and Sunnyside debris basin Do. Sunnyside debris basin and Carriage House debris basin Do. Hastings debris disposal area and Sierra Madre Villa Do. debris basin Kinneloa debris disposal area and Eaton debris disposal area Do. Eaton Reservoir above New York Dr. Do. West of Eaton Reservoir Do. Santa Anita debris basin Do. Sturtevant debris basin Do. Yucca Canyon Do. Carter Canyon West debris basin Do. Eaton Dam and Reservoir Do. Kinneloa East and Kinneloa West debris basins Do. Gooseberry debris basin Do. Rubio debris basin Do. Las Flores debris basin Do. Devonwood debris basin Do. Eaton Canyon and Allen Reservoir Do. Allen Reservoir Do. Tanoble Crib Dam Do. Gooseberry Creek Do. TABLES 123 TABLE 25. -Known aerial photographic coverage of southern California available from government agencies for the floods of January and February 1980-Continued Area of photography Date Los Angeles County Flood Control District, Los Angeles, California--Continued Las Flores debris basin and private drain 331 Feb. 20, 1980 Tujunga Wash--Foothill Blvd. to 1,500 ft + upstream Do. Mt. Gleason Ave. ~- Mandeville Canyon--Sunset Blvd. to Mulholland Dr. Do. Rustic Canyon--Pacific Ocean to 4 miles + above Sunset Blvd. Do. Topanga Canyon--Pacific Ocean to Glenview "Community" Do. Malibu Canyon--Pacific Ocean to Piuma Rd. Do. Zuma Canyon--Pacific Ocean upstream 2.4 miles + Do. Trancas Canyon--Pacific Ocean upstream C Do. Dry Canyon--Ventura Freeway to Calabasas Highlands Do. Arroyo Seco--Slide area Do. Santa Clara River--Ventura County line to San Martinez Chiquito Do. Canyon Santa Clara River--San Martinez Chiquito Canyon to Castaic Do. Junction Santa Clara River--Castaic Junction to Bouquet Junction Do. Santa Clara River--Bouquet Junction to Sierra Highway Do. (Mint Canyon) Santa Clara River--Sierra Highway to Bee Canyon Do. Santa Clara River--Bee Canyon to Mill Canyon Do. Santa Clara River--Mill Canyon to Aliso Canyon Do. Big Tujunga Reservoir and debris disposal area Do. Cogswell Reservoir Do. Cogswell Reservoir-Devil's Canyon Do. San Gabriel River West Fork-North Fork to Big Mermaids Canyon Do. Morris Reservoir--Morris Dam to San Gabriel Dam Do. San Dimas Canyon--Puddingstone Diversion Dam to San Dimas Do. debris deposal area Thompson Creek--Live Oak debris basin to Thompson Reservoir Do. Monterey County Flood Control and Water Conservation District, Monterey, California Carmel River from Carmel Village west to Pacific Ocean, June 1980 about 12 miles (River meanders caused by flood) 124 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TABLE 25. -Known aerial photographic coverage of southern California available from government agencies for the floods of January and February 1980-Continued Area of photography Date Riverside County Flood Control and Water Conservation District, Riverside, California San Jacinto River from just above Bautista Creek, the city of Feb. 21, 1980 San Jacinto and area downstream that was underwater, to 1 mile southwest of Perris Valley Airport Salt Creek from Railroad Canyon Reservoir upstream to just Feb. 23, 1980 west of Hemet Day Creek from Santa Ana River upstream to «)2 mile south Feb. 27, 1980 of Route 10 Temescal Creek from Prado Flood Control basin upstream Feb. 22, 1980 to just beyond Magnolia Ave. in Home Gard Murrieta Creek from confluence with Temecula Creek Feb. 26, 1980 upstream to Wildomar Temecula Creek from confluence with Murrieta Creek upstream Feb. 26, 1980 about 4.0 miles, including Pechanga Creek and other smaller tributaries from the south on the Pechanga Indian Reservation Lake Elsinore--Entire lake and peripheral area, extending Mar. 13, 1980 southeasterly toward Wildomar Palm Canyon Creek from just upstream from Highway 111 in Feb. 22, 1980 Palm Springs, upstream to about Hermits Beach in the Agua Caliente Indian Reservation. (Also, see Tahquitz Creek.) Tahquitz Creek from upstream from Highway 111 in Palm Feb. 27, 1980 Springs downstream to mouth; includes Palm Canyon Creek downstream from Highway 111 to mouth San Bernardino County Flood Control District, San Bernardino, California Harrison Canyon debris basin located at 40th St. and Jan. 19, 1980 Harrison Ave. in San Bernardino and area about 0.5 mile Feb. 1, 1980 wide by 2.0 miles long lying in a northeasterly direction Feb. 23, 1980 above the basin Mar. 13, 1980 Apr. 9, 1980 Prado Dam Reservoir on Santa Ana River Feb. 24, 1980 just after maximum storage occurred; consists of five verticals and four obliques, in color TABLES 125 25. -Known aerial photographic coverage of southern California available from government agencies for the floods of January and February 1980-Continued Area of photography Date U.S. Army Corps of Engineers, South Pacific Division, Los Angeles District, Los Angeles, California Lake Elsinore, perimeter of lake defined by high-water marks Feb. 27, 1980 U.S. Geological Survey, California District, San Diego Project Office, San Diego, California San Diego River from Pacific Ocean upstream to Route 67 Feb. 22, 1980 just east of Lakeside Cottonwood Creek from Barrett Junction (below Barrett Feb. 22, 1980 Reservoir) to confluence with Tecate Creek; then Tijuana River to international boundary Tijuana River from international boundary at Interstate 5 Feb. 22, 1980 to Pacific Ocean Ventura County Public Works Agency, Ventura, California Conejo Creek--Calleguas Creek to Hill Canyon Feb. 23, 1980 San Antonio Creek--Ventura River to the East Ojai Valley Feb. 24, 1980 Sespe Creek--Santa Clara River to Devils Gate Feb. 26, 1980 Canada Larga Creek--Ventura River to 5,000 ft upstream Feb. 24, 1980 Ventura River from mouth to Matilija Dam Feb. 24, 1980 Santa Clara River from mouth to Los Angeles County line Feb. 24, 1980 Calleguas Creek from Hueneme Rd. to Seminary Rd. Feb. 22, 1980 Arroyo Las Posas from Seminary Rd. to Hitch Blvd. Feb. 23, 1980 Arroyo Simi--Hitch Blvd. to Yosemite Ave. (Simi Valley) Feb. 23, 1980 Real Canyon (Piru)--Santa Clara River debris basin Mar. 31, 1980 Harmon Barranca (Ventura)--Santa Clara River to Santa Feb. 24, 1980 Paula Freeway Santa Paula Creek--Santa Clara River to Steckel Park Feb. 24, 1980 Arundell Barranca Flood Plain--Ventura Feb. 26, 1980 Revolon Slough--Pleasant Valley Rd. to Ventura Freeway Feb. 22, 1980 Beardsley Wash--Ventura Freeway through Wright Rd. Feb. 22, 1980 Nyeland Acres--Vicinity of Santa Clara Ave. and the Feb. 22, 1980 Ventura Freeway Pleasant Valley Rd.--Highway 1 to Camarillo Airport Feb. 22, 1980 Camarillo Airport--Vicinity of Camarillo Airport Feb. 22, 1980 Rice Rd.--Vicinity of Highway 1 and Rice Rd., Oxnard Feb. 22, 1980 Brown Barranca--Santa Clara River to Santa Paula Freeway Feb. 24, 1980 126 FLOODS OF FEBRUARY 1980 IN SOUTHERN CALIFORNIA AND CENTRAL ARIZONA TaBur 25.-Known aerial photographic coverage of southern California available from government agencies for the floods of January and February 1980-Continued Area of photography Date Ventura County Public Works Agency, Ventura, California--Continued Franklin Barranca--Santa Clara River to Telegraph Rd. Feb. Arundell Barranca--Pacific Ocean debris basin Feb. Piru Creek--Santa Clara River to Southern Pacific Feb. railroad tracks Grimes Canyon (Bardsdale)--Santa Clara River to 10,000 ft Feb. southerly Thacher Creek--Highway 150 to Thacher School Feb. Reeves Creek--Sieta Robles Tract to end of Reeves Rd. Feb. McNell Creek--Santa Antonio Creek to Los Padres Feb. National Forest Orcuit Canyon--Santa Clara River to headwaters Feb. 24, 26, 26, 26, 24, 24, 24, 26, 1980 1980 1980 1980 1980 1980 1980 1980 mmemscree - Ara i a Mone he he ints * Tv M Peer g be mh a / a Lal - gs a J s £ - , j Precambrian Geology and Bedded Iron Deposits of the Southwestern Ruby Range, Montana By HAROLD L. JAMES With a section on THE KELLY IRON DEPOSIT OF THE NORTHEASTERN RUBY RANGE U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1495 A synthesis of present knowledge of the Precambrian geology and mineral deposits of the southwestern Ruby Range, Montana UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1990 DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U. S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-In-Publication Data James, Harold Lloyd, 1912, Precambrian geology and bedded iron deposits of the southwestern Ruby Range, Montana. (U.S. Geological Survey professional paper ; 1495) "With a section on the Kelly Iron Deposit of the northeastern Ruby Range." Bibliography: p. Supt. of Does. no.: I 19.16:1495 1. Geology, Stratigraphic -Precambrian. 2. Geology-Montana-Ruby Range. 3. Iron ores-Montana- Ruby Range. I. Title. II Series. QE653.136 1989 551.7'1'097866 88-6000398 For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Page ADBEFACK ... ...... .... su ul lu sa revs sa alr a eus 1 | Geologic history-Continued Introduction kkk kkk. 1 Phanerozoic ........................... lal lll. lls Previous -work . ...s PFN 3 | Mineral resources ................................... General geology .................................... 8 TFOM . ...ll. lll l lulu lee aa aa a ee aaa a a ee aaa ae ees Archean rocks .......................... .. 00> 4 Tale :.... .is is ely ar apa ae b nee edie a e a nals Older gneiss and schist ....................... 5 Graphite klk kkk... ls Quartzofeldspathic gneiss ..................... 5 Other mineral deposits ........................... Christensen Ranch Metasedimentary Suite .. ..... 7 Nickel .... siir rre Quartzite ................................ 7T Corundum Iron-formation ............................ 8 ASb@StO8 ...... ...... lll lll kill.... Marble ll... s 11 Pegmatite minerals ........................... Undifferentiated metasedimentary rocks ...... 12 Base metals ...}. Quartz-mica schist and quartzose gneiss .. _ 13 | Kelly iron deposit, northeastern Ruby Range ............ Calc-silicate gneiss and schist ........... 14 Introduction Anthophyllite schist ... ................ 14 General geology ................................. Corre'latlon ............................... 15 Strata of the Christensen Ranch Metasedimentary Suite Ultran'nafif: FOCKS -s. .u. sl. ll. sel allen reac re vk 16 Dolomite marble .... Sfagtbogntzis's """"""""""""""""" is Garnet qumt.zite .and gnfaiss ................... Late Archean and (or} Early Proterbsoit(?) pegmatite -. p Horllxblenfde-dJOPmde gneiss .................... Middle Proterozoic diabase ........................ 19 oa. @rmabion se s .s.) pe Che neem tere 9 Tertiary strata .................................. 19 Quarlzite .... - nop nas oes c OA EEO NOO OAT AT A Igneous and meta-igneous rocks ................... Quaternary deposits ............................. 20 gn a gn 0.02220. 20.0... ll aid... 20 Ultramafic rocks .... Metamorphism |..................................... 21 Quartz fhonte """""""""""""""""" Prograde metamorphism .......................... 21 Pegmatite . nyr¥x gists na} ¥gk c+ 6k $k Orv e aud ¢ aa a+ Retrograde metamorphism ........................ 22 Strata of Paleozoic age ........................... Other metamorphic effects ........................ 22 StrUCtUre ...... ...... lll lll ll lll lvl lll lla. Geologic history .................................... 22 Post-Paleozoic faults .......................... Archean lalla l 22 Precambrian structures ........................ Proterozoi¢ | 24 | References cited ILLUSTRATIONS [Plates are in pocket] PraTE 1. Geologic map of the southwestern Ruby Range. 2. Geologic map of the Kelly iron deposit. Page FiGurE - 1. Map of southwestern Montana, showing approximate distribution of Precam- brian rock, outline of area of this report, and location of Kelly area 2 2. Map showing distribution of principal belts of iron-formation, southwestern Ruby Range, and localities of analyzed samples ............... 8 3. Photographs of iron-formation in outcrop ........................... 9 4. Histogram showing carbonate ratios of 32 samples of marble and other carbonate-bearing rocks of the Christensen Ranch Metasedimentary Suite, as estimated from X-ray analyses ..................... 12 5. Photograph of outcrop of Late Archean granite gneiss ................ 17 6. Geologic map of the Carter Creek iron deposit ....................... 26 7. Map showing location of principal talc mines and prospects in the southern Ruby Range 62 eels ca r aiken g 28 8. Stratigraphic section of the Christensen Ranch Metasedimentary Suite in the Kelly area kkk kkk ekke eae e ekke 32 9. Photomicrographs of rocks from the Kelly area ...................... 34 CONTENTS III IV TABLE i m. migo po +- yo. st CONTENTS TABLES Page Chemical analyses of quartzofeldspathic gneiss ...................... 6 Complete analyses of iron-formation ............................... 10 Partial ("rapid") analyses of iron-formation ......................... 11 Chemical analyses of metasedimentary rocks ........................ 13 Chemical analyses of Late Archean granite gneiss .................... 18 Chemistry of the iron-formation of the Carter Creek deposit, compared with other iron-formations ...................................... 28 Analyses of talc from deposits in the southwestern Ruby Range .... ... 29 Chemical analyses of metasedimentary rocks from the Kelly area . ...... 33 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS OF THE sOUTHWESTERN RUBY RANGE, MONTANA By HAROLD L. JAMES ABSTRACT The Ruby Range is one of a series of uplifted blocks in southwestern Montana that are cored by Precambrian crystalline rocks, mostly of Archean age. These uplifted blocks owe their origin largely to move- ment in Late Cretaceous and Tertiary time on steeply dipping range- bounding faults, and they are separated by broad valleys and basins containing locally deformed but unmetamorphosed strata of Phanerozoic age. The Precambrian crystalline rocks of the southwestern Ruby Range, an area of about 100 square miles, can be divided roughly into three northeast-trending belts, progressively younger to the west. The oldest and most easterly belt consists of an ill-defined sequence of Early(?) or Middle(?) Archean older gneiss and schist that underlies, with struc- tural conformity, a central belt underlain in turn by a rudely tabular mass of Middle or Late Archean quartzofeldspathic gneiss that forms the crest of the range for much of its length. The quartzofeldspathic gneiss is grossly layered and certainly of complex origin, derived in part from sedimentary precursors and in part from syntectonic granitic intrusions of at least two different ages. On a regional scale, this quartzofeldspathic gneiss forms a basement complex to an overlying sequence of metasedimentary strata that make up the most westerly of the three belts. The Middle or Late Archean metasedimentary sequence, here named the "Christensen Ranch Metasedimentary Suite," consisted originally of miogeoclinal-type sedimentary rocks, now represented by dolomite marble, diopsidic and hornblendic gneiss and schist, quartzite, mica and garnet schist, and banded iron-formation. These rocks are gener- ally well bedded, and distinctive individual lithologic units can be traced for miles. The appearance of a conformable succession, however, is misleading: original stratigraphic order has in large part been destroyed by displacements on bedding-plane faults and possibly by nappe development early in the structural history of the area. Amphibolite of Middle or Late Archean age is an abundant rock type, occurring as generally conformable screens and sheets, some as much as several thousand feet in thickness, in each of the three main rock groups. Most bodies are believed to have originated as mafic sills, of at least two, and probably of several, different ages. Ultramafic rock of Middle or Late Archean age occurs as small plutons in the ""older gneiss and schist" unit and as pods and lenses in the quartzo- feldspathic gneiss and Christensen Ranch Metasedimentary Suite; most of these bodies, if not all, were emplaced by plastic flowage and diatreme-type movement. Syntectonic Late Archean granite gneiss, some of it not readily distinguishable from older quartzofeldspathic gneiss, cuts the metasedimentary strata in a number of places and occupies extensive tracts near the range front in the southwestern part of the map area. Pegmatite of Late Archean and (or) Early Proterozoic(?) age is abundant, both as sheets and dikes of simple quartz-feldspar composition and as tourmaline-bearing pods and lenses, many of which are rudely zoned. The youngest Precambrian igneous rocks are diabase dikes of Middle Proterozoic age that occupy fractures related to a northwest-trending fault system. All rocks of the area, except for pegmatites and diabase dikes, are strongly deformed and metamorphosed to amphibolite facies. The dominant structures are northeast-trending isoclines, which are re- folded on north-trending axes; these may have been preceded by grav- ity slides and possibly nappe formation. The main orogeny, which was accompanied by syntectonic granitic intrusions, culminated in Late Archean time, about 2,750 m.y. ago. Later structural deformation con- sisted mainly of displacement on northeast- and northwest-trending faults, the latter active both in Precambrian time and during range uplift in late Mesozoic and Cenozoic time. Known or potential mineral resources include talc (which has been mined in a number of places), graphite, and banded iron-formation. The iron-formation has been explored extensively in the Carter Creek area; these deposits are estimated to contain, to a depth of 300 feet, about 95 million tons of rock containing 28-29 percent iron recoverable as magnetite. The Kelly iron deposit is in the northeastern part of the Ruby Range. Beds of iron-formation are contained in a conformable sequence of strata of the Christensen Ranch Metasedimentary Suite, here in nor- mal stratigraphic order. A thick basal dolomite marble passes upward through garnet-rich strata into diopside-hornblende gneiss that con- tains the principal iron-formation, and the gneiss in turn gives way to a sequence of quartzite beds that also contain thin layers of iron- formation. These strata are folded into a broad, southeasterly plung- ing syncline, the buried axial zone of which has been squeezed up, diatreme-fashion, to form a body of lens-like cross-section that is cored by a mass of ultramafic rock. The iron-formation in this upthrust block, greatly thickened by plastic flow and internal folding, has been ex- plored by test pits and drill holes, but despite a favorable composi- tion, the economic potential is low; the quantity, to a depth of 300 feet, is estimated to be about 15 million tons of protore containing 33 percent iron recoverable as magnetite. INTRODUCTION The Ruby Range is one of a number of uplifted blocks in southwestern Montana from which younger strata have been stripped, wholly or in part, to expose a Manuscript approved for publication August 10, 1988. 2 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA 112°00' 111°00° 45° 30° 45° 00 I Rives Bozeman, Area of figure 1 wind 0 10 10 20 MILES 20 KILOMETERS FIGURE 1.-Map of southwestern Montana, showing approximate distribution of Precambrian rock (diagonal line pattern), outline of area of this report, and location of Kelly area (X). Precambrian core that consists mainly of crystalline and metamorphic rocks of Archean age (fig. 1). These uplifts, their crest elevations ranging from about 9,000 to 11,000 ft, are separated by broad valleys and basins underlain in large part by continental deposits of Ter- tiary age. The Ruby Range is bounded by the valleys of the Beaverhead River on the west, Ruby River on the east, and Blacktail Deer Creek on the south. All streams flow northerly to the Jefferson River, a major tributary of the Missouri River. The southwestern part of the Ruby Range, the locus of the present study, is an area of relatively subdued upland topography; the maximum elevation is 8,530 ft, about 3,000 ft above the broad valley floors of the Beaverhead River and Blacktail Deer Creek. The nearest town is Dillon (population about 4,500), which is on a railroad line and at a junction of major highways. From these highways, dirt roads extend southeasterly across the range, following the principal drainage systems, Stone Creek in the north and Carter Creek- Sweetwater Creek in the central part of the mapped area. Secondary and tertiary routes traversable by small trucks and four-wheel-drive vehicles enter almost all parts of the area, but access commonly is by permis- sion only; much of the land is fenced and locked gates are common. Some land on the lower slopes is cultivated, but most of the area is open range, in part covered with sagebrush. Some areas of upland, par- ticularly in the southern and northeastern parts of the area, contain tracts of conifer forest, much of which is federal land managed by the U.S. Bureau of Land Management. Valley bottoms commonly are thickly overgrown with willow, alder, and cottonwood. Bedrock is generally fairly well exposed, though rarely in spec- tacular outcrop. This report is an outgrowth of field studies that began in 1960 with detailed plane-table mapping and mag- netometer surveys of the principal areas of banded GENERAL GEOLOGY 3 iron-formation in southwestern Montana, the results of which were made available through preliminary open- file reports (James and Wier, 1961, 1962; Wier, 1965) and by follow-up map releases (James and Wier, 19722, 1972b). Later in the 1960's, when 1:24,000-scale topo- graphic base maps became available, the work was broadened to cover more general aspects of the Precam- brian geology of the region, and, again, the results were made public through release of map data in preliminary form (James and others, 1969). Since then, U.S. Geo- logical Survey field work in the southwestern Ruby Range has been limited to brief re-examination of critical areas and to sample collecting for special pur- poses, such as isotopic age dating. The aim of the pres- ent report and map (pl. 1) is to provide a comprehensive overview of the geology and mineral deposits of that part of the Ruby Range that has been studied in detail, incorporating both the studies made by the U.S. Geo- logical Survey and by a number of independent workers over the past three decades. The freedom of access granted to U.S. Geological Survey field workers by the various ranchers and land- owners in the area during the course of these studies is gratefully acknowledged. A particular debt of grati- tude is owed to Arthur and Margaret Christensen, owners and operators of the Christensen Ranch, whose hospitality and assistance to the many geologists who have worked in this area during the last 40 years is legendary and in the finest tradition of the American West. PREVIOUS WORK The basic elements of the geology of the southwestern Ruby Range were established in the late 1940's and the 1950's by E.W. Heinrich and J.C. Rabbitt, working under the sponsorship of the Montana Bureau of Mines and Geology. This work resulted in a series of papers on special aspects of geology and mineral resources (Heinrich, 1948, 1949a, 1949b, 1950a, 1950b, 1963; Rab- bitt, 1948) and culminated in a monograph (Heinrich, 1960) that has remained a key reference on the geology of the region, a foundation for all future work. Work prior to that of Heinrich consisted mainly of studies and brief reports on certain mineral deposits: graphite (Winchell, 1910, 1911, 1914; Bastin, 1912; Armstrong and Full, 1946; Armstrong, 1950), nickel (Sinkler, 1942), and tale (Perry, 1948). The work of the U.S. Geological Survey that began in 1960 has already been noted. In part stimulated by the availability of new topographic base maps and by release of geologic data acquired in these U.S. Geolog- ical Survey investigations, the southwestern Ruby Range in the 1970's became the field base for a number of thesis studies by students from Pennsylvania State University (Okuma, 1971; Garihan, 1973; Karasevich, 1980), Indiana University (Dahl, 1977), and the Univer- sity of Montana (Bielak, 1978; Desmarais, 1978). Many of these theses led to formal publications (Garihan, 1979a, 1979b; Karasevich, 1981; Dahl, 1979, 1980; Dahl and Friberg, 1980; Desmarais, 1981). Of particular value to the present report are the maps in Garihan's 1979b paper (available formally only in microfiche) and the later synthesis published in the "1981 Field Conference Guidebook of the Montana Geological Society'" (Karasevich and others, 1981). Other reports and papers dealing with specific aspects of the geology of the Ruby Range will be referred to in appropriate context later in this report. Of major im- portance in a regional sense is the monumental compila- tion of the geology of the Dillon 1 °X2° quadrangle, now available in preliminary form (Ruppel and others, 1983). GENERAL GEOLOGY The general form and outlines of the Ruby Range, like those of other ranges in southwestern Montana and east-central Idaho, were established by block uplift along northwest- and northeast-trending faults that culminated in late Tertiary time (Ruppel, 1982) and by subsequent erosion. The core area of the range is underlain mainly by crystalline and metamorphic rocks of Archean age (James and Hedge, 1980), which trend generally northeasterly and dip steeply to the north- west. These rocks are transected by undeformed dikes of Middle Proterozoic age (Wooden and others, 1978) that follow or are structurally related to northwest- trending faults. Strata of Paleozoic and Mesozoic age are abundant- ly exposed in the northeastern part of the Ruby Range (Tysdal, 1976a, 1976b; Karasevich, 1981), but have been entirely stripped in the southwestern part. Clastic deposits of Tertiary age flank the range on the north- west, either in unconformable overlap or downdropped on the steeply dipping fault or faults of the northeast- trending, range-bounding system. The upland surface of the range and the gently sloping eastern flank local- ly are studded with flat-lying remnants of once more extensive basalt flows, at least some of which are of Pliocene age (Marvin and others, 1974). The Precambrian rocks of the map area can be divided loosely into three northeast-trending belts. The northwest-facing slope of the range is underlain main- ly by well-bedded sedimentary rocks that in the past (beginning with Winchell, 1914) have been designated "Cherry Creek Group'" (or "Series," in some older 4 PRECAMBRIAN GEOLOGY AND BECDED IRON DEPOSITS, RUBY RANGE, MONTANA reports) on the basis of assumed correlation with the Cherry Creek area on the eastern flank of the Gravelly Range, south of Ennis (see fig. 1). The crest of the range and much of the easterly sloping upland is underlain mainly by quartzofeldspathic gneiss, the Dillon Granite Gneiss of Heinrich (1960). This gneiss terrane is in turn bordered in discontinuous fashion to the southeast by a varied assemblage of crystalline and metamorphic rocks that Heinrich (1960) and most later workers have labeled simply "pre-Cherry Creek rocks" or "the pre- Cherry Creek group." These stratigraphic terms ("Cherry Creek," "Dillon," "pre-Cherry Creek") will not be used in this report, for reasons discussed in suc- ceeding paragraphs: Cherry Creek.-The strata of the Cherry Creek Group in the Cherry Creek area, described initially by Peale (1896), comprise a structurally complex sequence that contains a thick unit of dolomite marble, and quartzite, schist, and gneiss, and that has an aggregate thickness estimated by Peale to be "not less than several thou- sand feet."" The Cherry Creek area has been studied and remapped by many workers over the past 90 years (for example, Runner and Thomas, 1928; Sahinen, 1939; Heinrich and Rabbitt, 1960; Hogberg, 1960; Hadley, 1969; Bayley and James, 1973). These later studies have added much new information concerning rock types that comprise the assemblage, but little or no progress has been made in establishing a verifiable stratigraphic succession or in more precisely defining age relations to other Precambrian rocks of the area. An Archean age for the group can reasonably be assumed on the basis of regional studies (James and Hedge, 1980) but, aside from this, the sole criterion for extension of the term beyond the Cherry Creek locality has been the presence of dolomite marble. It was on this basis alone that cor- relation was proposed for dolomite-bearing sequences in the Tobacco Root Mountains and the Ruby Range by Winchell (1914), at a time when the vast duration of Precambrian time was little understood or appreci- ated. As discussed later in this report (see "Correla- tion"), there are major differences in rock succession and associations between the metasedimentary assem- blages of the Ruby Range and those of the Cherry Creek area. Later workers in the Tobacco Root Mountains (for example, Vitaliano and others, 1979; James, 1981) have abandoned the term "Cherry Creek" in favor of purely lithologic groupings. In this report on the Ruby Range, the strata previously labeled "Cherry Creek Group'" will be assigned a new stratigraphic term, the "Christensen Ranch Metasedimentary Suite." At some future date, criteria may be developed to prove equivalence of this suite to the Cherry Creek Group of the Cherry Creek locality, but these criteria are not now available. Dillon Granite Gneiss.-This term was introduced in a brief abstract by Heinrich (1953) to apply to certain intrusive bodies in the Ruby Range. Later, in a mono- graphic report on the area, Heinrich stated that the pre- Cherry Creek and Cherry Creek sequences "... are separated by a thick intrusive mass of granite gneiss, named the Dillon Granite Gneiss by the writer" (Heinrich, 1960, p. 16). The problem with the use of the term stems from uncertainty as to its proper definition. The description quoted above applies to the quartzofeldspathic gneiss of this report, which now is considered to predate the metasedimentary sequence (Cherry Creek). The original 1953 definition, however, clearly specified a younger age (post-Cherry Creek). Later workers (for example, Karasevich and others, 1981) have tended to ignore the age specification and have applied the term only to the basement quartzofeldspathic gneiss. It must be recog- nized, however, that present in the area are a number of granitic bodies that do conform to the original (1953) definition; these are much younger than the regionally extensive quartzofeldspathic gneiss. Presumably, the term could be redefined so as to limit its application, but it is unlikely that the possibilities for confusion could ever be eliminated. In this report, therefore, rock bodies previously labeled "Dillon Granite Gneiss" will be simply assigned appropriate lithologic terms: "quartzofeldspathic gneiss" for the main body underlying the Christensen Ranch Metasedi- mentary Suite, and "granite gneiss" for the generally smaller bodies that are intrusive into, or developed within, the metasedimentary strata. Pre-Cherry Creek rocks.-This assemblage was first described by Heinrich (1950a, p. 6) as consisting ". . . chiefly of injected and granitized gneiss, and horn- blende and biotite gneisses of various types . . .'' that were assumed, without specific evidence, to underlie strata then assigned to the Cherry Creek Group in the southwestern Ruby Range. The term "Pony series'" was applied to the assemblage by Heinrich on the basis of an assumed correlation with somewhat similar rocks in the Tobacco Root Mountains (Tansley and others, 1933), but in later reports, he replaced this term (now largely abandoned in the type area) with the designa- tion "pre-Cherry Creek rocks." Inasmuch as the term "Cherry Creek" has been rejected for formal use in this report, it is obvious that the extension "pre-Cherry Creek" is equally unacceptable. I have, however, fol- lowed tradition in separating this rock assemblage, assigning it (despite a dearth of evidence as to relative age) to a category labeled "older gneiss and schist." ARCHEAN ROCKS Most of the Precambrian rocks exposed in the Ruby Range are of Archean age (that is, older than 2,500 m.y.) GENERAL GEOLOGY 5 and range in character from well-preserved metasedi- mentary rocks to migmatite and banded gneiss of com- plex origin. The total time span represented by this diverse assemblage is not as yet known. The minimum age is about 2,750 m.y. (James and Hedge, 1980), but the possible lower age limit has not been established. In the Beartooth Mountains, about 100 mi to the east, rocks of similar character are older than 3,100 m.y., possibly as old as 3,300 m.y. (Reid and others, 1975). As noted in a previous section, the Archean-age rocks in the southwestern Ruby Range are disposed in three northeast-trending belts. A general age progression- oldest rocks in the east, youngest in the west-is as- sumed, largely on the basis of regional considerations; in fact, however, no unequivocal direct evidence for relative ages of these three belts has been identified. OLDER GNEISS AND SCHIST The principal outcrop of this group of rocks assigned an Early(?) and Middle(?) Archean age is in the south- central part of the map area (pl. 1), in the upland bordered on the north by the eroded scarp of the Carter Creek fault (extended). A smaller area, less certainly assigned to this category, lies about 1.5 mi to the north- east, across the Sweetwater Basin. Karasevich and others (1981) identify another area south of the Elk Gulch fault, extending to the topographic limit of the range, and Garihan (19792) has assigned a "pre-Cherry Creek" status to several square miles of gneiss on the eastern flank of the Ruby Range, centering on Cotton- wood Creek about 11 mi northeast of the principal out- crop area. The Cottonwood Creek locality provides the best exposures of this rock unit; it also illustrates the difficulties in separating this assemblage from the quartzofeldspathic gneiss of the central belt adjacent to the west. The lithology of the older gneiss and schist unit can- not be simply categorized. The assemblage is diverse, comprising biotite gneiss, augen gneiss, migmatite, hornblende gneiss, and amphibolite; Garihan (1979b, p. 725) notes additionally sillimanite-biotite-garnet gneiss, some containing cordierite. Probably the most abundant rock type, well exposed in the Cottonwood Creek locality noted above, is banded gneiss in which dark layers alternate with layers and pods dominantly of quartz and feldspar, some in pegmatitic aggregates. The banded gneiss and the associated rock types do not differ in any essential way from some components of the structurally conformable quartzofeldspathic gneiss that is immediately adjacent to the west. As a whole, however, as noted by Garihan (1979b, fig. 7), the assemblage tends to be somewhat more mafic and richer in plagioclase. It also tends to be more distinctly layered, and structural deformation-generally tight complex folding-is more conspicuous than in the more massive quartzofeldspathic gneiss of the central belt. The rocks exposed in the isolated area on the north side of the Sweetwater Basin (mostly in sec. 20, T. 8 S., R. 6 W.), questionably assigned to this map unit, are even more variable in character; they include sillimanite and anthophyllite schist, and, in the NEW sec. 20, corundum-bearing schist. The latter rock, exposed in scrapings on and adjacent to the Sweetwater road, con- tains zoned barrel-shaped crystals of lilac-colored cor- undum (sapphire), commonly about -in. diameter, in a matrix consisting mainly of quartz and mica. The only other known occurrence of corundum in the area of the present report is in sec. 36, T. 8 S., R. 8 W., where it occurs in biotite schist and marble of the Christensen Ranch Metamorphic Suite (for description, see Heinrich, 1950b, and later in this report). The parent rocks of the older gneiss and schist unit probably were in large part sedimentary, though a volcanic (or even plutonic) origin cannot be ruled out, particularly for the more homogeneous felsic layers. The hornblendic rocks (amphibolite and hornblende gneiss) here, as elsewhere in the region, probably are of diverse origins, some representing original mafic volcanic material, some younger dikes and sills that were meta- morphosed along with enclosing older strata. The sillimanite- and corundum-bearing schists, however, almost certainly were derived from aluminous shale, and much of the banded gneiss could be the metamorphic equivalent of impure quartzite and graywacke. Kara- sevich and others (1981), in their review of the geology of the Ruby Range as a whole, consider the protoliths of this rock unit to have been mainly impure sandstone and shale and conclude that this sequence originally graded upward into illitic quartz mudstone and siltstone now represented by the quartzofeldspathic gneiss of the central belt. QUARTZOFELDSPATHIC GNEISS This Middle or Late Archean rock unit, encompassed under the term "Dillon Granite Gneiss" in most earlier reports, forms the central northeast-trending belt in the Ruby Range, flanked on the east by older gneiss and schist and on the west by strata of the Christensen Ranch Metamorphic Suite. It is a tabular body, struc- turally concordant with adjoining rock units. The out- crop width ranges from about 2.5 to 4 mi, but this includes separately mapped bodies of amphibolite and narrow belts of infolded (or infaulted) dolomite marble of the Christensen Ranch Metamorphic Suite. Foliation and compositional layering dip rather consistently to the northwest at moderate to steep angles. 6 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA The dominant rock type, exposed in large rounded outcrops along the crest of the Ruby Range, is massive to foliated, medium-grained, gray to reddish brown gneiss of granitic composition. Rock textures, as seen in thin section, range from irregular to allotriomorphic granular, metamorphic in origin rather than igneous. The most abundant mineral generally is potassium feldspar, slightly to moderately perthitic, commonly with characteristic microcline grid twinning. The potas- sium feldspar is intergrown with oligoclase and quartz; typical proportions are 40:30:30, but vary widely among individual samples. Minor constituents are biotite (often altered to chlorite) and muscovite in scrappy small flakes, pink isotropic garnet, albite as rims to some oligoclase, fibrous sillimanite, and, in some specimens, nonperthitic microcline as small interstitial grains. Zir- con, apatite, and magnetite are the usual accessory minerals. Foliation is due to flattening of felsic minerals and to planar concentration of micas and garnet. Local- ly the texture is granoblastic; triple junctions between feldspar and quartz are not uncommon. The chemical composition of typical massive quartzofeldspathic gneiss from three localities is given in table 1. In the field, many variations from this characteristic rock type can be observed. Pods and layers of am- phibolite, many partly granitized, are a common feature in many outcrops and are particularly evident in the ax- ial zones of northeast-trending isoclinal folds. In places the normal quartzofeldspathic gneiss grades into band- ed gneiss containing more abundant dark minerals- biotite, garnet, and (more rarely) hornblende; elsewhere it grades into a felsic gneiss speckled with garnet. Discrete beds of diopside gneiss and quartzite have been found in a few places: these, like the separately mapped belts of dolomite marble, probably are structurally in- folded strata of the Christensen Ranch Metamorphic Suite, but this cannot be proved; they may represent initial precursor components of the gneiss terrane. Structurally, the typical foliated massive gneiss may give way to more profoundly deformed rock, such as felsic sillimanite-bearing schist or strongly lineated tec- tonite, the latter particularly well developed on axes of the north-trending folds that cross the dominant northeast-trending structures. Despite these variations, however, the bulk composition of the quartzofeldspathic gneiss clearly is granitic, as shown by the chemical analyses (table 1). On the basis of point counts for 73 samples, Garihan and Williams (1976) conclude that the average composition (in terms of the principal minerals) is 42 percent potassium feldspar, 31 percent quartz, and 27 percent plagioclase. The origin and even the relative age of the quartzo- feldspathic gneiss remains problematical. Heinrich (1960) unequivocally classed it as igneous, a "tabular TABLE 1.-Chemical analyses of quartzofeldspathic gneiss from the southwestern Ruby Range, Mont. [In weight percent. Analyst, Ann Vlisidis] 1 2 3 4 5 $10, 73/60: ... .. 74.048 «73:54 © 92.8 A1,03 137046 ~ Asp - thiss ~ ig"9 FeqO3 0.96 0.57 0.85 0.79 0.9 FeO 94 1.00 1.56 1.17 G Mgo . 30 15 63 .36 C Cao hs . 68 141 .83 13 Na,0 2.80 3.60 4.00 3.47 s K,0 6.00 5.70 3.10 -= "4.93 5.4 #,0~ . 10 . 04 . 08 . 07 n,0+ 18 16 22 19 TiO; 12 10 33 12 .4 P;O5 . 04 . 06 .05 .05 CO, 39 . 40 +37 39 Mno . 08 05 06 04 A Total 100.16 100.42 100.31 100.30 Sample data: 1. Quartzofeldspathic gneiss from large outcrops in SWl/4 sec. 6, T. 8 S., R. 6 W. Sample HJ-1-69. 2. Quartzofeldspathic gneiss from outcrop in sec. 16, T. 8 S., R. 6 W., approximately 1,100 ft east of center of section. Sample HJ-11-69, collected by Karen Wier. 3. Quartzofeldspathic gneiss from outcrop in NElL/4 sec. 6, T. 9 S., R. 7 W. on Timber Creek road. Sample HJ-16-69, collected by Karen Wier. 4. Average of analyses 1-3. 5. Average of 72 calc-alkalic granites (Poldevaart, 1955, p. 134). pluton" intruded between older gneiss and schist and the Christensen Ranch Metasedimentary Suite and therefore younger than either unit. Later work has cast some doubt on this interpretation. Garihan and Okuma (1974), noting the compositional heterogeneity of the gneiss, the structural concordance with adjacent strata, and the absence of skarn at contacts with dolomite, sug- gest that the gneiss represents "isochemically metamor- phosed arkosic rocks." In later papers, Garihan (19792, 1979b) made no clear choice between the igneous and metasedimentary alternatives, but in a subsequent GENERAL GEOLOGY l review of the geology of the entire Ruby Range (Kara- sevich and others, 1981), he joined L.P. Karasevich, P.S. Dahl, and A.F. Okuma in firmly opting for a sedimen- tary precursor (". . . a monotonous sequence of illite(?)- quartz mudstones or siltstones"). The view adopted in this report, following conclusions expressed in an earlier paper (James and Hedge, 1980) is that the gneiss is of diverse origins, in part derived from sedimentary and volcanic precursors and in part from granitic igneous intrusions, some (perhaps most) of which pre-date deposition of the sedimentary sequence now represented by the Christensen Ranch Metasedimentary Suite. On a regional scale, quartzofeldspathic gneiss appears to form a structurally conformable basement to dolomite- bearing metasedimentary sequences; this relation is evi- dent not only farther north in the Ruby Range (Karasevich, 1981), but also in the adjacent Gravelly Range (Wier, 1982) and to the north in the Tobacco Root Mountains (Vitaliano and others, 1979; James, 1981). CHRISTENSEN RANCH METASEDIMENTARY SUITE The strata that make up the suite are named for Christensen Ranch in T. 7 S., R. 7 W. and are well ex- posed on the northwest-facing slopes of the Ruby Range. Much of this area of exposure has been mapped in detail, primarily for the purpose of defining the distribution and economic potential of banded iron- formation (James and others, 1969; James and Wier, 1972b). The suite is recognized only in the report area. A secondary objective was to establish, if possible, a valid stratigraphic subdivision of this assemblage of distinctive metasedimentary strata of Middle or Late Archean age. The latter objective has not been achieved. It has been found that although the assemblage can readily be subdivided into mappable units, locally traceable in exquisite detail, no stratigraphic section can be established that will withstand critical analysis. A type area for the suite is designated as the northwest- facing slope of the Ruby Range between Stone Creek and Hoffman Gulch in T. 7 and 8 S., R. 7 W. Some of the difficulties encountered in defining formal units are those common to many areas of metamorphic rocks of complex history: general lack of internal evidence of time relations within or between beds (such as crossbed- ding or graded bedding), structural thinning and thickening due to flexural flow, and complex inter- ference patterns resulting from isoclinal folding and crossfolding. These difficulties can be overcome in many areas by precise mapping of distinctive lithologic units. In this case, however, the effort has proved unsuc- cessful. The conclusion appears inescapable that strati- graphic order within the sequence has in large part been disturbed or lost, probably mainly by transposition on unrecognized bedding plane faults, particularly at boundaries of structurally competent beds such as marble. Though not adequate for formal definition of strati- graphic units, some semblance of stratigraphic order does appear to be preserved, particularly if regional aspects are considered. From the Tobacco Root Moun- tains in the north, through the northern part of the Gravelly range and the adjoining northern part of the Ruby Range, and south into the area here being dis- cussed, quartzofeldspathic gneiss is in contact with dolomite marble, which may be the only recognizable metasedimentary rock present. Where metasedimen- tary strata are preserved in greater abundance and some local order can be established, the marble general- ly is succeeded by garnetiferous gneiss and schist, then by schist, gneiss, and quartzite containing one or more beds of banded iron-formation. Possible correlations are discussed later in this report. For the moment, suffice it to say that within the Christensen Ranch Metamor- phic Suite, the dolomite marble in immediate contact with quartzofeldspathic gneiss is considered to repre- sent the oldest rock in the initial sedimentary sequence and that it is overlain stratigraphically by strata that include banded iron-formation. For purposes of description and map display, the strata of the Christensen Ranch Metasedimentary Suite are subdivided entirely on the basis of lithology, without stratigraphic implications. Four categories are used: (1) quartzite, (2) iron-formation, (3) marble, and (4) undif- ferentiated metasedimentary rocks. The first three categories are of lithologically distinctive rocks, which may (and almost certainly do) occur at more than one stratigraphic position in the original sequence. The fourth category includes rocks as dissimilar as diopside gneiss and mica schist, which tend to form a matrix to the three separately mapped lithologic units. The esti- mated thickness of the suite is 6,400 ft. QUARTZITE Quartzite occurs throughout the suite in layers that range from ribs less than 1 in. thick in dolomite marble and mica schist to erosion-resistant beds as much as 100 ft thick. In the northwestern part of the map area, some of the most prominent beds persist without signifi- cant change in thickness for several miles, but thinner beds tend to pinch out in distances typically in the range of several hundred to several thousand feet. Quartzite ribs within dolomite marble commonly show metamor- phic reaction borders of white diopside, and indeed some thin layers may have been totally consumed by this process. Elsewhere, quartzite within dolomitic beds has been squeezed into thick lenses and boudins by tectonic deformation. 8 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA Other than bedding, now marked by slight color changes and by concentrations of micaceous minerals, no primary structures or textures are preserved in the quartzite. Neither crossbedding, expectable in rocks of this composition and association, nor conglomerate facies have been certainly identified. Most of the quartzite is white to yellowish brown and fine to medium grained. The texture ranges from sugary to vitreous, the latter only in more nearly pure varieties. Generally making up 90 percent or more of the rock, quartz occurs mainly as clear interlocking grains. Ad- ditional components of the rock are feldspar (typically sericitized and not readily identifiable as to type), muscovite, and chloritized biotite, all of which are pres- ent as small grains and flakes interstitial to quartz. Heavy minerals such as zircon are scarce. In a few places, quartzite containing fine flakes of green chrome mica has been noted, generally in beds too thin to show separately at map scale. Diopside characteristically is present in quartzite that is associ- ated with or interlayered with dolomite; with increased abundance the rock grades into light-colored diopside gneiss, often similar in appearance to quartzite. IRON-FORMATION Iron-formation is a quantitatively minor but distinc- tive component of the Christensen Ranch Metasedimen- tary Suite, within which it occurs as beds that range in true thickness from less than 1 ft to perhaps as much as 100 ft. Locally, because of complex folding and flex- ural flow, the apparent thickness is much greater. Though no definitive stratigraphic assignments are possible within the suite, on the basis of associated rocks it is apparent that iron-formation occurred at several levels in the initial sedimentary sequence. Most commonly, the iron-formation is interbedded with mica schist and quartzite, but some thin layers are entirely within dolomite marble: for example, a bed less than 5 ft thick is exposed within dolomitic strata in the NEVA sec. 10, T. 8 S., R. 7 W. and at the same stratigraphic posi- tion in the SW% sec. 9, T. 8 S., R. 7 W. The bulk of the iron-formation in the area occurs as belts within the two structural blocks defined by the Stone Creek, Carter Creek, and Hoffman Gulch faults (fig. 2). Though it cannot be demonstrated with certain- ty, it is likely that these belts shown in figure 2 repre- sent a single stratigraphic unit. As shown on the general geologic map (pl. 1), however, iron-formation has been located at many places elsewhere in the area. Quite possibly, some of these occurrences represent unre- solved structural repetitions of the main iron-formation; most, however, probably are separate stratigraphic units. REW RIN: 2 MILES 0 1 2 KILOMETERS FiGurRE 2.-Distribution of principal belts of iron-formation (gray), southwestern Ruby Range, and localities of analyzed samples. Underlined numbers, complete analyses (see table 2); others, par- tial analyses (see table 3); some from thin outlying beds not shown on map. The iron-formation of the area, regardless of strati- graphic position, typically is a dark, heavy rock in which quartz-rich layers 1 in. or less thick alternate with layers of similar thickness composed largely of magnetite. In detail, the layering is seen to be discontinuous, pinch- and-swell, complex folding, and structural transposition being common features (fig. 3). Locally, the layered structure gives way to yield a rock of streaky or gneissic aspect. Iron-formation is exposed in bold outcrops in the belt between the Carter Creek and Hoffman Creek faults, but more generally it is weathered to a subdued surface marked by a distinctive reddish-brown soil con- taining relict chips of magnetic material. Quartz and magnetite typically make up 75 percent or more of the rock by volume. Specularite is abundant in some samples but generally is scarce. Apatite, in GENERAL GEOLOGY 9 small discrete crystals, generally accounts for about 2 percent of the rock and commonly is concentrated in particular layers. The silicate suite is complex; it in- cludes both clinopyroxene and orthopyroxene, and a variety of amphiboles-cummingtonite-grunerite, ac- tinolite, hornblende, riebeckite, and sodium tremolite. Other minerals, rarely present in more than trace amounts, are epidote, biotite, chlorite, and feldspar. Garnet is absent in the typical banded iron-formation but may be abundant in associated garnet-grunerite schist. The texture of most iron-formation is fine- to medium-grained granular. Quartz, the dominant min- eral, is in anhedral grains that range from about 0.1 mm to 1 mm in mean diameter; other minerals are in grains of comparable or lesser size. Relations between the amphiboles are described in some detail by Ross and others (1969) and by Immega and Klein (1976), who show that the silicates of the metamorphic assemblage have been greatly modified by exsolution. Lamellae of cummingtonite in host ac- tinolite, actinolite in host cummingtonite, grunerite in FIGURE 3.-Iron-formation in outcrop. A, Banded iron-formation. Trenched outcrop in SW % sec. 30, T. 7 S., R. 6 W. B, Pinch-and- swell structures in iron-formation. Outcrop in NW % sec. 10, T. 8 S., R. 7 W. C, Complex folding in iron-formation. Outcrop in NW 4 sec. 10, T. 8 S., R. 7 W. host hornblende, and hornblende in host grunerite are reported. Riebeckite occurs as separate deep-blue grains and also as blue rims to light-green or bluish-green am- phibole (some possibly sodium tremolite). The pyrox- enes, which are relatively scarce and which have not been observed to occur together, consist of hypersthene and (more rarely) diopside-salite; neither shows exsolu- tion effects. Chemical data for iron-formation are given in tables 2 and 3. The table 2 analyses are of fresh, unoxidized material, selected so as to be representative of the rock as a whole; most samples are from drill core or explora- tion trenches. Analyses 1 and 4 are of rock containing abundant specularite, reflected in the analytical data by an excess of after maximum assignment of FeQ to form magnetite. The table 3 analyses are of out- crop samples, most of which are of partly oxidized material for which separate determination of ferrous and ferric iron would be relatively meaningless. Aside from this aspect, the data in the two tables show strik- ing concordance in chemical composition for the iron- formation in the southwestern Ruby Range. Of par- ticular note are the low contents of Al;,O; and MnO (less than 1 percent) and (except for analysis 4 in table 2) consistently high values for P;O;, compared with similar iron-formation elsewhere. The nature and sig- nificance of differences between iron-formation from the southwestern Ruby Range and that from the Kelly area of the northeastern part of the range are discussed fur- ther in this report, under "Correlation" and under ''Mineral Resources." PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA TABLE 2.-Complete analyses of iron-formation from the southwestern Ruby Range, Mont. [Samples from the northeastern Ruby Range (Kelly area) included for comparison. In weight percent; n.d., not determined. Analyst, Paula M. Buschman] Southwestern Ruby Range Northeastern Ruby Range (Christensen Ranch quadrangle) (Kelly area) 1 2 3 4 5 6 7 $10, 46.63 _ 44.02 45.20 64 . 34 36.80 - 40.00 39:58 A1,03 0.84 0.66 0.73 0.29 3.80 1.99 2.47 FeqOq 30.99 32.29 38.05 28.61 27.71 32.07 FeO 13.38 - 17.14 10.99 5.08 23.26, <18.87 19.22 MgO 3,32 3.21 2.14 1.00 3.60 2.46 2.41 CaO 2.46 1.37 1.22 43 2.14 1.87 1.90 Na,0 1:10 . 06 . 58 A9 0.15 0.12 0.09 K,0 21 . 02 .21 . 00 1.03 . 56 85 n,0+ . 40 . 50 27 10 . 29 S31 33 H,0~ . 08 . 04 . 03 . 04 . 20 £15 .16 TiO; . 02 . OL . O1 fol 27 . 08 710 P305 . 38 55 . 51 . 02 . 07 .10 . 09 MnO . 07 . 04 . 06 . 03 63 43 175 CO» . 10 15 . O1 . 00 17 15 .16 Cl . OL . 00 . O1 n.d. . 00 . 00 . 00 F 02 02 02 n. d OL OL OL . 00 . 00 . 00 n. d. . 07 03 .10 C 00 02 OL n. d 00 00 02 Subtotal 100.01 100.10 100.05 99.94 100.20 100.30 100.31 Less 0 . O1 . O1 . O1 =-- . 04 . 02 . 05 Total 100.00 100.09 100 . 04 99.94 100.16 100.28 100.26 Fe 32.08 - 35.90 35.15 23.96 37.46 _ 37.60 37437 Mn 0.05 0.03 0.05 0.02 0.49 0:57 0.58 Sample data: 1. Drill core from angle hole in SEl/4NEL/4 sec. 9, T. 8 Sample 181-60. w 2. Drill core from vertical hole in SEL/4NEL/4 sec. 9, T. 8 S., R. 7 W. Sample 182-60. 3. From trench in NEL/4SEl/4 sec. 9, T. 8 S., R. 7 W. Sample 183-60. 4. From outcrop in SE1l/4 sec. 3, T. 8B S.,; R. 7:W., 200 ft E., 50 ft N. of S$1/4 cor. sec. 3. Sample 834-72. 5. Drill core from angle hole in NWLI/4NEL/4 sec. 25, T. 6 S., R. 5 W. footage 435-445 ft. Sample 188-60. 6. Drill core from same hole as above, footage 633-643 ft. Sample 189-60. 7. Drill core from second angle hole in NWL/4NEL/4 sec. 25, T. 6 S., R. 5 W. Sample 190-60. GENERAL GEOLOGY 11 TABLE 3.-Partial ("rapid") analyses of iron-formation from the southwestern Ruby Range, Mont. [In weight percent; <, less than. Analyses by Claude Huffman, Jr., project leader. Total Fe determined volumetrically and reported as MgO, CaO, Na,0, K,0, and MnO by atomic absorption; P;0, determined colorimetrically; total S and C determined by induction furnace] 1 2 3 4 5 6 7 $10, 41.8 43.6 43.3 43.3 43.5 51.6 58.4 A1,03 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 Fe,O3 57.3 57.5 49.3 49 . 2 50.5 46.1 40.9 MgO 0.34 0.59 4 . 43 2.94 3.78 1.80 0.63 CaO 1.21 .92 1.23 1.52 1.32 0.99 52 Na,0 fol .02 0.15 0.18 0.15 fol . 04 K,0 . 02 . 04 . 04 . 05 . 06 . OL . 04 MnO . 04 . 09 .27 .55 . 42 . 02 <.0L P305 75 . 26 . 49 .71 . 63 .77 .37 S <.05 <.05 <.05 <.05 <.05 <.05 <.05 C in B . 05 . 05 <.05 . 09 . 05 . 09 Total 102 104 100 99 101 102 101 (Rounded) Fe 40.1 40 . 2 34.5 34 . 4 35.3 32.31 28.61 Mn 0.03 0.07 0.21 0.43 0.33 0.0L 0.00 Sample data (see also fig. 2): 1. Sample 114-72: SW1/4 sec. 8, T. 7 S., R. 6 W., 3,300 ft S., 100 ft E. of NW cor. 2. Sample 124-72: NEl/4 sec. 18, T. 7 S., R. 6 W., 1,750 ft S., 1,400 ft W. of NE cor. 3. Sample 134-72: SW1l/4 sec. 17, T. 7 S., R. 6 W., 1,300 ft N., 850 ft E. of SW cor. 4. Sample 14A-72: SWl/4 sec. 30, T. 7 S., R. 6 W., 500 ft N., 2,000 ft E. of SW cor. 5. Sample 154-72: NEl/4 sec. 35, T. 7 S., R. 7 W., 1,600 ft S., 2,000 ft W. of NE cor. 6. Sample 814-72: SEl/4 sec. 3, T. 8 S., R. 7 W., 1,700 ft W., 3,100 ft S. of NE cor. 7. Sample 824-72: SW1l/4 sec. 3, T. 8 S., R. 7 W., 1,100 ft E., 700 ft N. of SW cor. MARBLE abundant) tremolite, and scarce small flakes of graphite. Marble constitutes the most prominent component of the Christensen Metasedimentary Suite, within which it occurs as steeply dipping belts as much as several thousand feet in outcrop width. The rock is massive to well bedded and white, gray, or buff; bed- ding is marked by textural and compositional dif- ferences, in many places by ribs of quartzite and of white diopside. Exposed rock surfaces characteristically are speckled with bright-orange lichen. The texture varies, but most commonly it is fine- to medium-grained granular, weathering to smooth cuspate surfaces com- monly lightly sprinkled with loose grains of carbonate. Locally, however, the rock may be very coarse grained, individual crystals being as much as 1 in. in diameter. Marble of the area typically contains small to moderate amounts of light-colored diopside and (less Serpentine, in dark-green rounded blebs (presumably secondary after forsterite) is characteristic of certain beds, and phlogopite is abundant in some impure varieties of marble. Other minerals noted in some samples are quartz (as separate clastic grains in calcite marble and preserved in the interior parts of diopside- bordered ribs in dolomite marble), hornblende, plagioclase, scapolite, clinozoisite, and, very rarely, garnet. Heinrich (1960, p. 21) reported local abundance of thulite. Most marble and other carbonate-bearing rocks in the area contain both calcite and dolomite, but in propor- tions, as estimated by staining tests and X-ray analyses, that range widely. The results, determined by an X-ray technique utilized by Gulbrandsen (1960) and refined by Royse and others (1971), for 32 randomly selected samples are summarized in figure 4. 12 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA Consideration of the analytical data in relation to the nature of material sampled leads to certain generalizations: 1. Most thick beds of relatively pure marble and diop- sidic marble are dominantly dolomitic in composi- tion, and some are virtually free of calcite. There are exceptions, however; for example, a 100-ft-thick bed of arenaceous marble that crosses Stone Creek in the SE% sec. 18, T. 7 S., R. 6 W. has a calcite- dolomite ratio of about 95:5. 2. Discrete layers of marble as much as 5 ft thick inter- bedded with diopside gneiss and other cale-silicate rocks generally are dominantly calcitic. 3. Carbonate-bearing gneiss and schist contain both calcite and dolomite in widely varying (and seem- ingly unpredictable) proportions. Much of this variation is believed due to the extent of dedolomiti- zation reactions during metamorphism and to the relative initial abundance of dolomitic and siliceous constituents in the precursor rock. In many places in the area, marble has been exten- sively affected by post- metamorphic hydrothermal processes, producing three different kinds of mineral associations: 1. Formation of talc and related minerals-Tale is widespread in the dolomitic marble units as seams, pods, and lenticular bodies, some of which are of economic significance (see further under "Mineral Resources"). The tale is light colored, locally bluish or greenish; associated minerals are chlorite and serpentine. Talc mineralization in places is accom- panied by siliceous veining of the marble and by development of very coarse grain sizes of the con- stituent dolomite. 2. Formation of serpentine and cross-fiber chrysotile in silicate-rich marble at and near contacts with Middle Proterozoic diabase dikes-The chrysotile forms discontinuous veinlets as much as 0.5 in. across that are limited to zones a few feet wide, sporadically distributed along marble-diabase con- tacts. A number of occurrences have been explored by shallow test pits, as in secs. 35 and 36, T. 7 S., R. 7 W.; these reveal material of mineralogic interest but of little or no economic consequence. 8. Silicification along northwest-trending faults, which has produced masses of brown jasperoid as much as 800 ft wide along the Carter Creek fault and long screens of iron-stained silicified breccia 50 ft or more wide along the Stone Creek fault. The age of the silicification is not known for certain, but much of it appears to have resulted from warm spring ac- tivity that accompanied or post-dated late Tertiary movement on the faults. Minor amounts of azurite and malachite present in parts of the breccia along 10 NUMBER OF SAMPLES 0 0 20 - 30 . 40 - 50 60 70 80 90 100 WEIGHT PERCENT DOLOMITE Calcite Dolomite FIGURE 4.-Carbonate ratios of 32 samples of marble and other carbonate-bearing rocks of the Christensen Ranch Metasedimen- tary Suite, as estimated from X-ray analyses. the Stone Creek fault have led to some exploration, including a short adit across the fault zone in the SEV sec. 21, T. 7 S., R. 6 W. The stratigraphic significance of the marble remains uncertain. As stated previously, the facts of regional distribution in the Ruby Range, Gravelly Range, and Tobacco Root Mountains (which comprise a nearly con- tinuous exposure of Precambrian rocks) indicate that dolomite marble immediately overlies a presumed base- ment of quartzofeldspathic gneiss. On this basis, the marble that is in immediate contact with, or chiefly enclosed in, the quartzofeldspathic gneiss of the south- western Ruby Range is interpreted as the basal member of the Christensen Ranch Metasedimentary Suite, in- folded or infaulted. It is to be noted that quartzite is scarce or lacking in this particular marble. Elsewhere in the area, however, notably in the refolded fold center- ing in sec. 24, T. 7 S., R. 7 W., marble is in immediate association with one or more beds of quartzite of map- pable dimensions. Other belts of marble are in close stratigraphic proximity to iron-formation and schist. These diverse lithologic associations suggest that in fact marble occupies more than one, possibly as many as three, stratigraphic positions in the initial sedimen- tary sequence, of which only one (the basal unit) is preserved on a regional scale. UNDIFFERENTIATED METASEDIMENTARY ROCKS The strata assigned to this category are those which, in essence, form interbeds to the more prominent or more distinctive lithologic units, such as marble, that have been separately mapped. The undifferentiated strata are grouped as follows: (1) quartz-mica schist and quartzose gneiss, including sillimanitic, garnetiferous, and corundum-bearing varieties, derived from initial GENERAL GEOLOGY 13 sediments of shale or sandy shale composition; (2) calc- silicate gneiss and schist (and retrograde products that include para-amphibolite and hornblende-epidote gneiss), derived from shaly carbonate sediments; and (3) anthophyllite schist of uncertain origin. Each of these groupings is in itself complex, and in the aggre- gate, coupled with the separately distinguished quartz- ite, marble, and iron-formation, they reflect an almost complete range of sedimentary rock compositions in the initial depositional suite. The local presence of scapolite suggests that this initial assemblage may even have in- cluded an evaporitic component. QuarTz-Mica Schist Anp QuarRTzOsE GNEISS These rocks, most of which contain abundant mica, comprise a substantial percentage of bedrock in the area but in general are poorly exposed. All are well-foliated rocks, typically made up mainly of quartz, biotite, plagioclase, and potassium feldspar in varying propor- tions. Sillimanite and garnet are also common constitu- ents. Corundum, staurolite, and muscovite are present in some samples. Accessory minerals include tour- maline, apatite, zircon, and magnetite; sericite, chlorite, and epidote are local alteration products. Irregular lenses and seams of granitic composition are a charac- teristic feature in many outcrops of schist, the result of local granitization (or homogenization). In places the felsic constituents are dominant and the rock assumes a gneissic aspect. Sillimanite-bearing schist is widespread in the area, in places forming outcrop belts hundreds of feet wide, as for example in SEV% sec. 34, T. 7 S., R. 7 W. The sillimanite occurs as fibrous bundles, in part as an ap- parent replacement of biotite, and it typically con- stitutes about 5 percent of the rock. Table 4 (analysis 1) presents a chemical analysis of sillimanite schist from the area. The high content of K,0 in the sample (8.56 weight percent) is reflected in the mineralogic makeup by abundant potassium feldspar; the precursor rock probably was an illite-rich shale. In places sillimanite occurs as disc-like aggregates or lenses that range in maximum dimension from 1 in. or so to 1 ft or more. Larger masses consisting mainly of sillimanite are found in outcrop and associated rubble in an area of sillimanite schist in the SE% sec. 24, T. 8 S., R. 8 W., at the head of what is known locally as "Proffitt Gulch." Heinrich (1950a) describes the locality in detail and estimates some of the sillimanite masses ("'dornicks") to weigh as much as 600 pounds. Garnet is a common constituent of the mica schist and quartzose gneiss of the area and in many places is a major constituent, occurring as reddish-brown TABLE 4.-Chemical analyses of metasedimentary rocks from the southwestern Ruby Range, Mont. [In weight percent. Analyst, Paula M. Buschman] 1 2 $10, 60.56 51.22 A1,04 16.17 10.54 Feq0q 0.85 3.81 FeO 6.68 3.50 Mgo 2.47 9.54 Cad .21 11.80 Na,0 1.05 1.28 K,0 8.56 4 . Al n,0+ 1.53 1.00 #,0~ . 20 0.08 TiO; .83 . 70 P,05 . 04 15 Mno .03 13 co, . O1 1.50 Cf . O1 . 01 F .09 .10 . 00 . 00 C 06 14 Subtotal 99.35 99.91 Less 0 __. 04 . 04 Total 99.31 99.87 Sample data: 1. Biotite-sillimanite schist from low roadcut in NW1/4SEL/4 sec. 3, T. 8 S., R. 7. W., 780 ft E., 1,990 ft N. of S1/4 cor. sec. 3. Sample HJ-185-60. 2. Epidote-hornblende-feldspar-quartz gneiss from outcrop in NW1/4NEL/4 sec. 10, T. 8 S., R. 7 W., 130 ft E., 820 ft S. of NL/4 cor. sec. 10. Sample HJ- 184-60. poikilitic crystals, some of which are rudely euhedral. Larger crystals-not uncommonly 2-3 in. in diameter- tend to accumulate in the soil and surface wash adja- cent to weathered outcrops. Coarse-grained garnet is particularly abundant in the schist that bounds the syn- form of marble in sec. 2, T. 8 S., R. 7 W. This schist con- tinues in a northeast-trending belt separating parallel units of marble, where it is interlayered with garnet- quartz-feldspar gneiss and garnet amphibolite. These 14 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA various garnet-rich rocks probably have been derived from iron-rich shale, locally arenaceous. An unusual corundum-bearing rock, in part enclosed in schist and in part in dolomite, is exposed near the northeast corner of sec. 36, T. 8 S., R. 8 W. This rock is described by Heinrich (1950b, p. 13) as follows: The gray corundum rock consists mainly of elongate corundum crystals scattered abundantly throughout a dense, exceedingly fine- grained matrix. Under the microscope the corundum-bearing rock can be seen to consist of individual grains and crystals of corundum, often zoned, set in a generally fine-grained matrix that consists of sericite, chlorite, margarite, calcite, and rare granules of magnetite. The rock occurs as lenticular bodies in a belt as much as 20 ft in outcrop width and 220 ft in length. The only other known corundum in the area is in schist ques- tionably assigned a pre-Christensen Ranch age (see previous discussion under "Older Gneiss and Schist"). At that locality-sec. 20, T. 8 S., R. 6 W.-the corun- dum similarly occurs as lilac-colored, barrel-shaped crystals in schist, but marble is absent from the associated strata. The rock at both localities, however, can be assumed to have been derived by metamorphism from aluminous shale. CaLc-SILIcATE GNEISS Anp ScHIsT In this category are placed the diverse rock types derived by metamorphism from argillaceous dolomite and dolomite-bearing shale and sand. Physically, rocks of this suite range from erosion-resistant greenish-gray diopside gneiss to fissile brown, green, or gray schist. Diopside gneiss is a common rock type in the area, grading variously into diopside quartzite, diopside- tremolite marble, or phlogopite-tremolite-diopside schist, depending upon the relative amounts of clay, sand, and carbonate in the precursor sediment, and into foliated amphibolite and epidote gneiss in localities of strong retrograde metamorphism. Diopside gneiss (and many of its variants) is well exposed in northeast- trending belts that cross sec. 10, T. 8 S., R. 7 W., where they alternate with parallel belts of dolomite marble and ortho-amphibolite (see James and Wier, 1972b, for details of distribution). In outcrop the rock is dark greenish gray, weathering to greenish brown, and generally layered on a scale of inches or feet. In thin section, the rock is seen to be a fine- to medium-grained granoblastic aggregate consisting mainly of gray diop- side and quartz, and variable amounts of potassium feldspar, tremolite, brown-orange mica (generally assumed to be phlogopite), and calcite. Other constit- uents of fairly common occurrence are garnet, plagio- clase, and scapolite; sphene, tourmaline, and magnetite are the typical accessory minerals. Grain diameters vary from sample to sample, but generally are in the range 0.1-0.7 mm. These various assemblages, initial equilibrium products of amphibolite-grade regional metamorphism, have been altered to varying degrees by retrograde metamorphism, in places enough to significantly change the character of the rock. The com- mon retrograde minerals are actinolite or hornblende (which replace diopside), epidote, chlorite, and sericite. In places, as in the SWMANW!¥/ sec. 27, T. 7 S., R. 7 W., alteration has produced hornblendic rock that physical- ly is similar to the ortho-amphibolite of the area. The usual partial preservation of diopside and of some car- bonate, however, reveals its metasedimentary ancestry. In another example, the resultant rock is epidote- hornblende gneiss, such as that exposed on the southeast-facing slope of the iron-formation ridge in the NW!%/ sec. 10, T. 8 S., R. 7 W. A chemical analysis of a sample from this locality, where the gneiss contains 1 in.-thick interbeds of pink calcite marble, is given in table 4. The high content of K,0 is unusual and is reflected in the mineralogic makeup of the rock by abundant untwinned potassium feldspar, now altered in considerable part to secondary clay minerals and sericite. Another metamorphic product of impure dolomitic sediments is phlogopite schist, a fissile rock that dif- fers mineralogically from gneissic units mainly in the relative amounts of mica and platy amphiboles. It dif- fers also in certain associations; in places it grades into biotite-quartz schist of similar appearance. The rock, rarely well exposed, is gray or greenish on fresh break but weathers brown. Foliation commonly is deformed into complex nonsystematic crumples. A typical sam- ple, collected from the poorly exposed belt of schist that extends northeasterly through the SWW4SW!W/ sec. 30, T. 7 S., R. 6 W., consists, in order of abundance, of quartz, diopside, pale-brown to orange-brown phlogo- pite, and colorless to pale-green actinolite, and accessory blue-green tourmaline and magnetite. Elsewhere, simi- lar schist may contain small to moderate amounts of calcite, pink garnet, potassium feldspar, or muscovite. ANTHOPHYLLITE SCHIST Anthophyllite-bearing rocks are quantitatively a very minor component of the Precambrian strata of the southwestern Ruby Range, but they are a distinctive feature, described in many reports beginning with that of Rabbitt (1948). Outcrops of the rock tend to be small and isolated, and relations to enclosing strata usually are obscure. The rock is strongly foliated, made up largely of light-brown to reddish-brown anthophyllite in platy aggregates. The origin of this curious rock is not always clear, but it is found in two quite different associations, both of which reflect metamorphism GENERAL GEOLOGY 15 (prograde or retrograde) of magnesium-rich precursors, which may have been either igneous or sedimentary. Anthophyllite schist is found in close proximity to bodies of ultramafic rock throughout the area. In the idealized situation described by Desmarais (1981), the anthophyllite is a transitional mineral phase, forming an inner zone between unaltered ultramafic rock and an outer hornblendic or biotitic zone. This zonal alteration records chemical transfer during metamorphism be- tween the ultramafic intrusive and the host country rock. This ideal pattern is, however, rarely observed; more commonly, particularly where the intrusive bodies were small, the reaction may have consumed virtually all of the initial ultramafic rock, leaving only an- thophyllite schist and related hornblendic rocks. Antho- phyllite schist of this type is found as small lenses, rarely more than a few feet or a few tens of feet wide, at a number of places within areas of undifferentiated metasedimentary rocks, notably in secs. 2, 15, and 16, T. 8 S. R. 7 W. Anthophyllite schist of metasedimentary origin is confined to areas of extensive retrograde metamor- phism of diopside gneiss and schist, products of prograde metamorphism of argillaceous dolomite or dolomitic shale. Rock of this paragenesis has been recognized in a few areas, for example in outcrops in the SWWM4SW!/ sec. 27, T. 7 S., R. 7 W., near the Sweet- water road. Here the anthophyllite rock forms a nar- row zone separating dolomite marble from massive pegmatite. Some parts of the zone consist almost wholly of coarse-grained bladed anthophyllite, beige to light gray in thin section; other parts contain, in addition to anthophyllite, coarse-grained pink garnet, minor quartz, and accessory magnetite. CORRELATION The preservation of many distinctive sedimentary features in the Christensen Ranch Metasedimentary Suite offers tantalizing prospects for application of stratigraphic principles and for regional correlation based on stratigraphic analysis. In the southwestern Ruby Range, despite good exposure and detailed litho- logic mapping, the initial hope of achieving a valid stratigraphic subdivision of the suite has not been realized, principally because of lack of internal in- dicators of age relation within and between beds and because of probable major displacements on unrecog- nized bedding plane faults. Nevertheless, as discussed previously, some rude correlations may be possible, based mainly on regional distribution and mutual relations between dolomite marble and the quartzo- feldspathic gneiss that is believed to be the older rock. This association is in nearly continuous exposure, interrupted only by some structural breaks, from the area of the present study northward into the northeast- ern Ruby Range (James and Wier, 1972a; Karasevich, 1981), into the adjoining part of the Gravelly Range (Wier, 1982), and thence northward into the Tobacco Root Mountains (Vitaliano and others, 1979; James, 1981). In each case, except for the Gravelly Range, dolomite marble is overlain by garnet-rich schist and gneiss, which are succeeded by metasedimentary rocks that include iron-formation and quartzite. Within this rudely correlatable sequence, traceable for about 35 mi, the only probable direct equivalent is the basal dolomite marble, and even this interpretation is open to some question. Aside from the possibility that the relation between the dolomite marble and the quartzofeldspathic gneiss is structural rather than stratigraphic (that is, that the marble is the lower unit of a thrust sheet or nappe of regional dimensions), the marble exhibits considerable differences from one area to another, particularly in thickness. The true strati- graphic thickness in the southwestern Ruby Range has not been determined, but it may range from less than 200 ft to 2,000 ft or more. In the northern Ruby Range, notably in the area of Ruby Peak in secs. 16 and 17, T. 6 S., R. 5 W., the apparent thickness is about 2,500 ft, whereas in the central Tobacco Root Mountains it generally is less than 100 ft. The iron-formation units, often considered key elements in regional correlation, are in fact sufficiently different in occurrence, composi- tion, and association from place to place as to cast serious doubt on stratigraphic equivalency. In all, it is concluded that although physical continuity and gen- eral character indicate that the metasedimentary assem- blages in the northern part of the Ruby Range and in the Tobacco Root Mountains are at least in part strati- graphically equivalent to those of the Christensen Ranch Metasedimentary Suite, more specific correla- tions are not warranted. The possibility of correlation between the Christensen Ranch Metasedimentary Suite and the Cherry Creek Group of the eastern Gravelly Range, some 60 mi to the east and separated by major structural breaks, remains an open question. The assemblages are of rudely equiva- lent age and both contain banded iron-formation and thick units of dolomite marble. In detail, however, major differences are apparent, notably in relative position of the dolomite and iron-rich strata. In the Christensen Ranch Metasedimentary Suite (and its extensions to the north) bedded iron-formation is in a sequence that over- lies a basal dolomite marble, whereas the opposite is true in the Cherry Creek area. A partial succession for the latter area, where stratigraphic order is established by crossbedding in quartzite and pillow structures in 16 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA greenstone, in order of increasing age is as follows (from Bayley and James, 1973): Thickness, in feet Lithologic unit (approximate) Dolomite ... ...>... ...t. s ien r . 2 or 1,000 Phyllite 0 ri,. cl 50 Greenstone ::. ; ...!... s." .s esata n' sin ikl 700 }.; .. ;s a. va uH Pals alel aa none 100 Phyllite, with thin layers of iron-formation ...... 200 Banded iron-formation ........................ 35 Phyllite, with one or more layers of crossbedded green quartzite ...s... SLI Tae ry a - >500 Bed-by-bed correlation of strata in the two areas clear- ly can be discounted. The possibility remains, however, that the strata may in fact be age-equivalent and that the differences now observed reflect initial facies changes in a sedimentary basin of regional extent. ULTRAMAFIC ROCKS Intrusive bodies of ultramafic composition assigned to the Middle or Late Archean are found throughout the area. Most are small pods or lenses a few tens of feet in length and width, but irregularly shaped bodies as much as 1 mi in maximum dimension are present in the southeastern part of the map area, where they make up the Wolf Creek pluton of Heinrich (1960, 1963). In outcrop the rock is dark and massive to schistose; sur- faces commonly are rough and studded with weather- resistant pyroxene grains. The ultramafic bodies were emplaced prior to at least the termination of the last major regional deformation and metamorphism. Schist- osity, which may be limited to marginal areas in larger bodies, is parallel to that of the enclosing rocks; original textures and minerals generally are well preserved only in the interior parts. The initial rocks ranged from harzburgite to pyrox- enite in composition, depending upon relative amounts of olivine and pyroxene, but in most places these have been modifed extensively by serpentinization and post- emplacement metamorphism. The mineral assemblages are described in some detail in Desmarais (1981), and the following discussion is drawn in part from that work. In the larger bodies the least altered rock consists of poikiloblastic orthopyroxene set in a finer grained matrix of olivine, orthopyroxene, magnesio-hornblende, spinel, and magnetite. The olivine (Fogs-Fogy) and the orthopyroxene (En,;;-Eng;) are relatively rich in iron, compared to those typical of alpine peridotite. The spinel, green in thin section, has a generally high con- tent of alumina; Cr/(Al+Cr) ranges from 0.019 to 0.150. In the larger bodies, this relatively unaltered core grades outward in a series of reaction zones having the following generalized sequence: (1) anthophyllite rock, locally containing calcium amphibole; (2) hornblende- or gedrite-rich rock, locally containing garnet; and (3) biotite-rich schist. These alterations reflect exchange reactions between the intrusive ultramafic rock and the enclosing gneiss during metamorphism. Other reaction products include clinohumite, actinolite, serpentine, and talc. Desmarais (1981, p. 73) also notes the occurrence of rodingite lenses composed of clinozoisite, epidote, diopside, grossularite, vesuvianite, and actinolite, cut by veins containing chlorite, sphene, calcite, and prehnite. Yellow-green crusts of annabergite have been recognized on surface exposures of the Wolf Creek pluton (Sinkler, 1942; Heinrich, 1960); a number of shallow test pits have been sunk in the area to investi- gate the extent of the nickel mineralization. It is likely that most of the ultramafic bodies, and almost certainly all those occurring as lenses and pods in strata of the Christensen Ranch Metasedimentary Suite, were emplaced tectonically by plastic flow rather than by intrusion of magma. Ultramafic diatremes are known elsewhere in the region, as for example in the northeastern Ruby Range and the Tobacco Root Moun- tains (James and Wier, 1972a; James, 1981), where they are located in axial areas of major folds in metasedimen- tary rocks. However, the larger masses in the southwest- ern Ruby Range occur within strata believed to be the oldest Precambrian rocks of the region, and structural control of their location within those strata is not im- mediately obvious. The possibility must be entertained, therefore, that this terrain was the original site of ultra- mafic emplacement, whether by plastic flow or as magma, and that subsequent orogenic movements re- sulted in breakup and boudinage of initial intrusive bodies and emplacement as "pumpkin seed" lenses and pods throughout the quartzofeldspathic gneiss and the Christensen Ranch Metasedimentary Suite. This model, here tentatively adopted, is consistent with the highly complex mineralogic record worked out by Desmarais (1981). AMPHIBOLITE Amphibolite of Middle or Late Archean age occurs throughout the area, in bodies that range in size from layers and lenses too small to show at 1:24,000 map scale to sheets as much as 3,000 ft in outcrop width that are traceable for miles. In outcrop the rock is massive to moderately well foliated, having a salt-and-pepper ap- pearance. Grain size is variable, mostly from medium to coarse, and in part appears to reflect original dif- ferences in the parent rock. The other major difference observable in outcrop is in the amount of garnet, which ranges from nearly zero to as much as 25 percent. Most of the amphibolite is mineralogically simple, con- sisting of about equal parts green hornblende and plagioclase (oligoclase-andesine), which together make up 90 percent or more of the rock. Quartz content ranges GENERAL GEOLOGY 17 from 5 to 10 percent, and biotite is present in trace amounts. Accessory minerals are apatite and magnetite. Garnetiferous amphibolite is more variable: in addition to the garnet, hornblende may make up as much as 60 percent of the rock and quartz may be more abundant than plagioclase. Both types of amphibolite locally have been extensively altered by retrograde metamorphism: sericite and epidote replacement of plagioclase; chlorite, actinolite, and epidote replacement of hornblende. A third, less common type of amphibolite contains variable amounts of diopside and (in some specimens) carbonate, and sphene as a typical accessory. This rock is believed to be a para-amphibolite that owes its origin to retro- grade metamorphism of diopside gneiss, which in turn was derived from a sedimentary precursor. Other than the diopside-bearing variety, most of the amphibolite is considered to have been derived from mafic igneous rock (the classic reference for amphibolite grade metamorphism). Some thin layers may represent metamorphosed basaltic flows or tuffs, but most bodies probably were emplaced as diabase or gabbro sills. At least two, and probably several, epochs of mafic intru- sion are represented. The latest is recorded by a single dike, exposed in secs. 22 and 23, T. 7 S., R. 7 W., which transects northwest-trending strata that include con- formable amphibolite of earlier age. This dike rock, now a foliated amphibolite, probably is equivalent to "meta- basite"' intrusive bodies farther north in the Ruby Range (Garihan, 1979b) and to metamorphosed but undeformed mafic dikes in the Horse Creek area of the Tobacco Root Mountains (Cordua, 1973). The amphibolite, despite its generally massive aspect, was structurally mobile during deformation, so that much of the apparent thickness variation of individual sheets is due to plastic flow. Direct evidence of plastic flow is provided by the abundance of amphibolite lenses, arcuate in plan view, aligned along crests of major struc- tural axes. A number of amphibolite "horse collars" of this type are found along the northeast-trending fold axis in quartzofeldspathic gneiss in the NW! sec. 7, T. 8 S., R. 6 W. GRANITE GNEISS Granite gneiss of Late Archean age, much of it not physically distinguishable from older quartzofeld- spathic gneiss (parts of which may in fact have been remobilized in the Late Archean orogeny), is found as (1) sills and concordant lenses in strata of the Christen- sen Ranch Metasedimentary Suite; and (2) as larger masses developed in or engulfing quartzite-bearing strata of the range-front terrain in the southwestern part of the map area. In both occurrences the rock is typically medium grained, gray or brown in outcrop, and at least moderately foliated parallel to the struc- ture in adjacent strata (fig. 5). In a few places, however, the rock is strongly sheared, virtually mylonitic. Granite gneiss of category (1) above is typified by the sill that is exposed in small but prominent outcrops in the NW !%/ sec. 31, T. 7 S., R. 6 W. and by sills in dolomite marble in secs. 1 and 2, T. 8 S., R. 7 W. The rock of the sec. 31 locality, as seen in thin section, is medium to coarse grained and has an allotriomorphic or irregular texture. It is composed principally of nonperthitic microcline, quartz, and oligoclase (about Ans), all of which commonly show minor fracturing and some grain-margin granulation. Foliation is defined mainly by small flakes of dark-brown biotite and minor muscovite. Accessory minerals, mainly magnetite and zircon, are scarce. Trace amounts of fibrous sillimanite are present. Much more strongly deformed rock is observed in the sills in dolomite marble. Specimens from a sill exposed near the W! cor. sec. 1, T. 8 S. R. 7 W. are of a thoroughly granulated rock in which quartz is drawn out in parallel strings several millimeters in length. Microcline and plagioclase (oligoclase) occurs both as fractured large grains and as small recrystal- lized interstitial grains, and the rock contains a small amount of pink garnet. Alteration to sericite and chlorite is extensive. Chemical compositions of granite gneiss from these two localities are given in table 5, col- umns 1 and 2. Granite gneiss of category (2) underlies larger areas and probably is polygenetic in origin. Some appears to have been developed in place, the product of granitiza- tion or partial melting of pre-existing pelitic strata, now represented by relict layers of quartzite. The larger part, however, is of igneous origin, occurring as sheet-like FiGuRE 5.-Outcrop of Late Archean granite gneiss. Axes Canyon, SW! sec. 24, T. 8 S., R. 8 W. Outcrop is about 70 ft high. 18 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA TABLE 5.-Chemical analyses of Late Archean granite gneiss from the southwestern Ruby Range, Mont. [In weight percent. Analyst, Ann Vlisidis; Na,0 and K,0 determined by Rapid Rock Laboratory, under Leonard Shapiro] 1 2 3 4 5 6 $10, 71.50 72.62 72.04 76.04 73.05 72:3 A1,03 16.47 14.42 12.31 11.76 13.74 13.9 FeqO3 0.59 1.03 1.58 1.43 1:16 0.9 e 78 1.48 2.97 1.16 1:59 217 Mgo 47 0.43 0.84 0.41 0.54 78 Cao 2.07 1.72 1.78 78 1.59 1.3 Na,0 4.7 2.5 2.4 233 2.27 3.1 K,0 6 4.9 4.9 5.4 4.45 5.4 #,0~ . 06 . 08 . 04 . 02 . 05 n,0+ . 20 .24 .26 . 28 . 24 TiO; 18 18 . 66 .29 +33 4 Mno . 03 . 07 . 08 .05 . 06 CO, 34 . 48 17 .24 3% P505 . 07 . 07 17 Ans . 09 4 Total 100.03 100.22 100 . 20 100.21 100.17 Sample data: 1. From sill in schist 69. 2. From sill in dolomite marble in NW1l/4 sec. 1, T. 8 S., R. Sample HJ-2-69. 3. From sheet-like body in SWl1/4 sec. 24, T. 8 S., R. 13-69. From same locality as 3. 5. Average of analyses 1-4. in NW1/4: sec: 31, T. :7 ° R. 6 W. Sample HJ-4- 6 W. 8 W. Sample HJ- Sample HJ-14-69. 6. Average of 72 calc-alkalic granites (Poldevaart, 1955, p. 134). masses of medium-grained, moderately well foliated rock that in thin section is seen to be composed mainly of finely perthitic microcline, plagioclase (andesine, about Anse, gradationally zoned to albite margins), and quartz, with lesser amounts of biotite and green horn- blende. The texture is irregular and many grains show fracturing. Accessory minerals-apatite, allanite(?), magnetite, and zircon-are relatively abundant, and garnet is not rare. The chemical compositions of two samples are given in table 5, columns 3 and 4. The average composition of the four analyzed samples (table 5) is not significantly different from the average composition of older quartzofeldspathic gneiss (table 1), and both closely resemble that of the average calc-alkali granite quoted by Poldevaart (1955, p. 134). LATE ARCHEAN AND (OR) EARLY PROTEROZOIC(?) PEGMATITE Pegmatites are abundant in the area, and, as early recognized by Heinrich (1949a, 1949b, 1960), two vari- eties can be distinguished: (1) older pegmatite, which occurs as thick concordant sheets and straight-walled dikes, yellowish weathering and of simple composition; and (2) younger pegmatite, which occurs as smaller pod- like bodies that commonly are rudely zoned to quartz- rich cores. Older pegmatites, which are the more abundant of the two varieties, typically consist almost entirely of coarsely crystalline perthitic microcline and quartz, and minor amounts of albite-oligoclase as separate grains. GENERAL GEOLOGY 19 Muscovite, tourmaline, and garnet generally are absent but are scarce constituents in some samples. Most bodies show some cataclastic deformation, evident in both outcrop and thin section, and a few bodies are foliated parallel to contacts with country rock. Pegmatites classed as "younger" are more complex in mineralogy and in internal structure. Samples suffi- ciently fine grained to be worth thin-section study con- sist of interlocking grains of perthitic microcline, twinned plagioclase (oligoclase-albite), and quartz, and variable amounts of tourmaline (black in hand specimen, pleochroic in dark green and brown in thin section), and muscovite. Rose quartz is common in core zones, which may contain large crystals of tourmaline and muscovite, together with lesser amounts of brown garnet and bluish-green apatite. A number of the zoned pegmatites have been explored by shallow pits and trenches, presumably to assess the economic possibilities for com- mercial production of sheet mica. The older, more abundant pegmatites are assigned a Late Archean age. General cataclasis and local develop- ment of foliation suggest that they were intruded at the end stage of a Late Archean orogeny, which has an age of about 2,750 m.y. (James and Hedge, 1980). The younger pegmatites post-date this 2,750-m.y. event and are cut by diabase dikes having a Rb-Sr age' of about 1,424 m.y. (Wooden and others, 1978). Isotopic measure- ment on muscovite from a zoned pegmatite in sec. 3, T. 8 S., R. 7 W. yielded a K-Ar age of 1,660 m.y. and a Rb-Sr age' of 1,646 m.y. (Giletti, 1966, sample 8). Whether these values reflect time of crystallization is not known for certain. As Giletti (1966) has shown, the Archean strata of southwestern Montana west of the Gallatin River show isotopic evidence of a thermal event of about this age, and it is not unreasonable to assume that it was accompanied locally by generation of pegma- tite magma. MIDDLE PROTEROZOIC DIABASE Diabase dikes transect the generally northeasterly trends of crystalline rocks in the area and clearly are related structurally to the northwest-trending fault system. A few follow faults directly, but many others are in en echelon fractures in zones parallel to major breaks. Thicknesses (as measured in outcrop width) are as much as 500 ft, but most are less than 100 ft. In- dividual dikes rarely are traceable for more than 1 mi or so, but many separate bodies may be aligned along the same structural trend. The rock is not resistant to erosion: outcrops are rare, but dike trends commonly 'Recalculation, based on decay constant of 1.42X10'uyr'1. are well marked by topographic sags and by presence of spheroidally weathered boulders. All of the diabase is altered extensively to second- ary minerals, but original diabasic or gabbroic textures are well preserved. The initial mineral assemblage con- sisted of augite, now largely altered to actinolitic amphibole and chlorite; plagioclase (labradorite), now gradationally zoned to albite and altered to clinozoisite and sericite; minor quartz; and accessory magnetite and ilmenite, the latter as exsolution lamellae now altered to leucoxene. Contact effects on country rock are relatively in- significant except where dikes cross silicate-bearing dolomite marble; here the marble for a few feet adja- cent to the contact is irregularly altered to serpentine that in places contains veinlets of cross-fiber chrysotile asbestos. The diabase dikes of this area are part of a swarm of generally northwest trending dikes that cut older Precambrian rocks of the Ruby Range and of the adja- cent Tobacco Root Mountains to the north. Wooden and others (1978) class the diabase in the Ruby Range as "low potassium tholeiite'" and give an average composi- tion as follows (in weight percent): SiO, __ 48.6 TiO, 1.10 Al,O, _ 14.2 FeOp - 11.5 MnO 0.19 Mgo 7.54 Cad __ 12.1 Na,0 _ 1.92 K,0 0.38 Whole-rock Rb-Sr analyses yielded an isochron' of 1,424 m.y.+125 m.y. and an initial ratio of 0.7019+0.0008. TERTIARY STRATA Rocks of Tertiary age flank the crystalline core of the southwestern Ruby Range and locally are preserved on upland surfaces. These strata have not been studied in detail and are here described in summary fashion only. The beds that flank the range on its northwest margin consist of weakly lithified siltstone, sandstone, and con- glomerate. Their precise age is not known, but similar strata at the north end of the Ruby Range are Eocene to Pliocene (Petkewich, 1972). These strata are dropped down on the northeast-trending range-bounding fault system and continue westerly to underlie the intermon- tane Beaverhead basin. Where exposed along valley walls, beds are generally horizontal or gently dipping, but near the contact with the Precambrian they are 20 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA tilted at angles as great as 30° on minor faults. The main Tertiary-Precambrian contact, however, is general- ly masked by the mantle of Quaternary gravel and debris on the pediment surface that bevels both older and younger rocks and by Quaternary alluvium in the valleys. Locally, as in the SE % sec. 28, T. 7 S., R. 7 W., the basal Tertiary strata are in exposed unconformable contact with Precambrian crystalline rocks on the up- thrown side of the range-bounding fault. Basalt, remnants of valley flows, is found in isolated patches in the western and northwestern parts of the map area and in more extensive outcrop along the eastern margin. The basalt in the latter occurrence is probably equivalent to basalt flows in sec. 7, T. 9 S., R. 5 W., about 6 mi to the southeast, which yield a Pliocene whole-rock K-Ar age of 4.2 m.y.+0.2 m.y. (Marvin and others, 1974). Basalt now found in small patches in a 3-mi-long belt that extends from sec. 2, T. 8 S., R. 7 W. to sec. 19, T. 7 S., R. 6 W. appears to repre- sent a separate flow (or flows) that filled a (then) northeast-trending valley, locally covering coarse talus of crystalline rocks. Throughout the map area the basalt is of similar character. Typical samples contain pheno- crysts of olivine in a fine-grained matrix made up mainly of plagioclase laths and pyroxene granules. QUATERNARY DEPOSITS Two types of surficial deposits are distinguished on the general map of the area (pl. 1): basin fill and stream alluvium. A third category, not separately mapped, con- sists of colluvial debris that mantles pediment surfaces on lower slopes of the range. The basin deposits are largely confined to the eastern part of the map area, where they underlie a wide area of low relief in the upper reaches of the Sweetwater Creek drainage system. Exposures are very poor. The material revealed in some gully walls consists largely of unconsolidated, poorly bedded sand and gravel con- taining a substantial amount of volcanic ash. The thickness is not known, but probably is generally less than 100 ft. Deposition of these clastic deposits postdates late Tertiary movement on the Stone Creek and Carter Creek (extended) faults, which displace basalt of Pliocene age. The originally continuous upland (peneplain?) surface was displaced about 600 ft on the Carter Creek (extended) fault to form the Sweetwater basin and provide a site for clastic accumulation. Stream deposits, consisting of sand and gravel augmented by slumped debris from valley walls, are found as narrow strips along a number of streams in the area. They are not regularly distributed, and some probably accumulated in local basins formed by land- slide damming of streams. STRUCTURE The main outlines of the Ruby Range and the pattern of the principal drainage systems reflect late Mesozoic and Tertiary movement on northeast- and northwest- trending faults. Within the range itself, however, the fabric is controlled mainly by a general northeast trend of layering, foliation, and fold axes, modified by north- trending crossfolds and by Middle Proterozoic move- ment on faults of the northwest-trending system. Little is known in detail of the northeast-trending fault that bounds the range on the northwest. It is generally assumed to be a steeply dipping normal fault, northwest side down, on which there was recurrent movement during Tertiary and Quaternary time (Ruppel, 1982), but the possibility exists (J.M. O'Neill, written commun., 1987) that the fault was active in late Mesozoic (Laramide) time, with high-angle reverse movement, northwest side up. Movement evidently ter- minated prior to development of the present pediment surface, which truncates all rocks and rises gradational- ly from the Beaverhead basin toward the range crest. There is no evidence for Precambrian movement on this fault. The northwest-trending fault system is of regional im- portance throughout eastern Idaho and southwestern Montana (Ruppel, 1982). The main faults of this system in the southwest Ruby Range-the Stone Creek, Carter Creek, Hoffman Gulch, and Elk Gulch faults-are an- cient; all were active in Precambrian time, with consis- tent left-lateral displacements, measurable in thousands of feet, that occurred prior to emplacement of Middle Proterozoic diabase dikes. Movement on at least the Stone Creek and Carter Creek faults was later renewed, possibly in late Mesozoic (Laramide) time but certain- ly in the late Tertiary. As previously noted, the Carter Creek fault (extended) cuts a basalt flow of Pliocene age a few miles beyond the east margin of the map area; vertical displacement, northeast side down, is about 600 ft. Springs are common along both the Stone Creek and Carter Creek faults, both of which are marked by zones of silicification-silicified breccia on the Stone Creek fault and jasperoid on the Carter Creek fault. Much of this silicification postdates or is contempora- neous with late Tertiary movement on the faults, but some, such as jasperoid along the Carter Creek and Hoffman Gulch faults, could in part be older, possibly of Laramide or even of Precambrian age. All of the strata comprising the crystalline core of the range, including the massive quartzofeldspathic gneiss, have been intensely deformed. Folds of several genera- tions and orientations are evident, both in outcrop and (more particularly) in map patterns. The oldest iden- tifiable structures are isoclinal folds that trend and METAMORPHISM 21 plunge northeasterly and have axial planes that dip to the northwest. There is some evidence that this fold system is the product of more than one period of defor- mation, as indicated, for example, by refolded folds in the marble belt in the eastern part of sec. 12, T. 8 S., R. 7 W. and the adjoining sec. 6, T. 8 S., R. 6 W. Garihan (1979b) suggests that the initial structures were at least locally recumbent, a concept expanded by Karasevich and others (1981) to include formation of nappes. The northeast-trending isoclines (including those of the marble belt noted above) are further deformed by crossfolds that trend and plunge to the north. The resultant structures are upright, tight to open folds, best exemplified by the major synform that centers in sec. 24, T. 7 S., R. 7 W. Deformation on this fold set was locally intense, as shown, for example, by strong rodding of quartzofeldspathic gneiss in sec. 12, T. 8 S., R.: 7 W. Other structural trends are less readily defined. Some apparent fold structures of odd orientation probably are simply geometric consequences of refolding of earlier folds, interference patterns rather than reflections of dif- ferent stress fields. Broad arching, however, as in the terrane north of the Stone Creek fault and that between the Carter Creek and Hoffman Gulch faults, is a separate structural element of northwesterly trend; it reflects internal adjustments within fault blocks to the extensive left-lateral Precambrian movement on the northwest-trending faults. The major uncertainty encountered in analysis of the Precambrian structural evolution of the southwestern Ruby Range concerns the reality and possible extent of an early epoch of low-angle deformation. Physical evidence bearing on the issue is scarce. It consists main- ly of small-scale rootless folds locally present in layered gneiss, having axial planes parallel to layering and folia- tion, which can be interpreted as relict fragments of re- cumbent structures, and of certain map patterns, as in the belt of marble that crosses sec. 6, T. 8 S., R. 6 W. No widespread mylonitic zones that might identify detachment surfaces have been found, although as noted by Karasevich and others (1981), apparent absence could be due either to nonrecognition of a thin mylonite layer or to distribution of the cataclasis through a thicker zone of ductile shear. Lacking positive physical evidence, the argument for an early low-angle structural displacement in the southwestern Ruby Range rests on two principal bases: (1) Anomalous field relations between major lithologic units, such as those of the Christensen Ranch Metasedi- mentary Suite, that indicate that the initial strati- graphic succession has been strongly disturbed, probably in large part by displacements at boundaries of competent lithologic units and by sequence reversals due to complete overturn of some sheets. As a conse- quence, the observed structures are no longer amenable to analysis based on stratigraphic consistency and continuity. (2) Mounting evidence that such an event may have taken place on a regional scale. The conclusions reached by Karasevich and others (1981) calling for nappe struc- tures in the northern Ruby Range have already been noted. Reid (1957) and Burger (1967) have proposed an initial epoch of recumbent folding for a similar assem- blage of Precambrian strata in the Tobacco Root Moun- tains, as has Erslev (1983) for the southern Madison Range to the east. On the basis of this rather fragile framework of fact and inference, it is concluded that the Precambrian strata of the area were first deformed by low-angle displacements, including at least local recumbent fold- ing, then tightly compressed into the now-dominant northeast-trending isoclines, which are co-axial (but not coplanar) with the initial structures. A synthesis of the structural evolution of the area, placed in the context of total geologic history, is presented in a succeeding section of this report. METAMORPHISM All of the Precambrian strata of the area, except pegmatites of Late Archean or Early Proterozoic(?) age and Middle Proterozoic diabase dikes, have been metamorphosed to upper amphibolite facies. Because of the great variety of rock types and the wide range of chemical compositions represented, the area is a vir- tual field laboratory for studies of metamorphism. Outstanding papers have been published on a number of different aspects: metamorphosed iron-formation (Im- mega and Klein, 1976), metamorphosed ultramafic rocks (Desmarais, 1981), mineralogy (Rabbitt, 1948; Ross and others, 1969; Dahl and Friberg, 1980), and geothermometry (Dahl, 1979, 1980). The discussion that follows draws largely from these sources, coupled with personal observation and use of the synthesis prepared by Karasevich and others (1981) for the Ruby Range as a whole. PROGRADE METAMORPHISM The assemblages that were produced by metamor- phism during the Late Archean orogeny (culminating age about 2,750 m.y.) can be assigned to the sillimanite-potassium feldspar zone on the basis of the association sillimanite-perthitic microcline in quartz- feldspar gneiss and schist and by the general absence 22 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA of prograde muscovite. Kyanite is generally absent but has been preserved as a relict phase in some metapelite (Dahl, 1979). During the cycle of prograde metamor- phism, ultramafic rocks were deserpentinized, then converted to assemblages containing olivine, ortho- pyroxene, magnesio-hornblende, and spinel (Desmarais, 1981). Mafic rocks were metamorphosed to amphibolite, composed chiefly of hornblende, andesine, quartz, and garnet; pyroxene is generally absent. Typical prograde assemblages in iron-formation consist of quartz, magnetite, and grunerite (cummingtonite), and variable amounts of specularite, riebeckite, hypersthene, and ac- tinolite. Rock of dolomitic composition was converted, depending upon the initial content of sand and clay, to marble (containing variable amounts of forsterite, diop- side, and tremolite), diopside-tremolite-phlogopite schist, and diopside-feldspar-quartz gneiss. Appraisal of the ultramafic assemblage leads to an estimate of peak metamorphic conditions as being about 710 °C, 5-7 kbar pressure (Desmarais, 1981). Ele- ment distribution between garnet and pyroxene, garnet and biotite, garnet and hornblende, and alkali feldspar and plagioclase indicates values for peak conditions to be 645+45 °C, 6.2+1.2 kbar (Dahl, 1979, 1980). These temperature-pressure conditions-about 700 °C, 6 kbar-are typical of those generally assumed for amphibolite-facies metamorphism (Miyashiro, 1973, p. 90). The estimated temperature is about 50 °C lower than that estimated for the northern part of the Ruby Range, where rocks are in the granulite facies (Karasevich and others, 1981). RETROGRADE METAMORPHISM All of the prograde assemblages have been modified to a greater or lesser degree by retrograde metamor- phism: forsterite is altered to serpentine, pyroxenes to amphiboles and epidote, amphiboles to epidote and chlorite, biotite to chlorite and muscovite, feldspars to clinozoisite and sericite. Amphiboles in iron-formation show complex exsolution (Ross and others, 1969; Immega and Klein, 1976). Cordierite occurs locally as retrograde coronas on garnet; iron-magnesium distri- bution indicates a temperature of 545+50 °C at equilibrium (Dahl, 1979). Oxygen isotope fractionation between magnetite and quartz in iron-formation yields an estimated temperature of 475+25 °C (Dahl, 1979). The significance of these various retrograde altera- tions is not entirely clear. Some of the phenomena (ex- solution of amphiboles, cordierite coronas on garnet, and oxygen isotope distribution, for example) probably can be attributed to continued chemical and mineralogic reaction during the slow decline of temperature from peak conditions. Other effects, however, notably the widespread epidotization and hornblendization of diop- side gneiss, are believed to represent a separate, later cycle of metamorphism superimposed on the earlier prograde assemblages. A reasonable assumption is that this later cycle occurred in response to a regional thermal rise that has been dated at about 1,650 m.y. (Giletti, 1966). OTHER METAMORPHIC EFFECTS All of the Middle Proterozoic diabase dikes in the area have been incompletely but extensively altered to a greenschist assemblage. Since these dikes postdate the 1,650-m.y. thermal rise and inferred accompanying epoch of retrograde metamorphism, it is evident that the region was affected by a still later metamorphic cycle of at least moderate intensity. A late Precambrian (Late Proterozoic or Late Middle Proterozoic) age can be assumed, since Paleozoic rocks in the Ruby Range are not altered, and it is possible that the widespread deposits of tale were formed at this time. GEOLOGIC HISTORY ARCHEAN The geologic history of the area prior to the Late Ar- chean orogeny that culminated about 2,750 m.y. ago is known only in broad outline and at present entirely lacks geochronologic tie points. Elsewhere in the north- ern Rocky Mountains, mainly in the Beartooth Moun- tains of Montana and Wyoming, some elements of older geochronology have been established: Mueller and others (1985) present data that suggest that supra- crustal rocks of the eastern Beartooth Mountains, which include quartzite and iron-formation, were metamorphosed to granulite facies about 3,400 m.y. ago; Page and Ziontek (1985) conclude that the Still- water Complex (age about 2,700 m.y.) was emplaced in an iron-formation-bearing sedimentary sequence to which a minimum age of 3,270 m.y. is assigned; and Reid and others (1975) show that metasedimentary rocks of the North Snowy block, which include marble, have a minimum age of about 3,100 m.y. and were in- vaded by granite gneiss having an age of about 3,000 m.y., well before the Late Archean orogenic event. These data are fragmentary, but they do indicate a com- plex regional history of sedimentation, magmatism, and metamorphism that spans at least 700 m.y. of Archean time. GEOLOGIC HISTORY 283 The Archean history of the Ruby Range can be ex- pressed only in sequential terms, based on known or in- ferred relations between rock units. The reconstructed record is as follows (oldest to youngest): 1. Deposition of intermediate to mafic volcanic and volcaniclastic strata, together with interlayered graywacke-type sediments, to form the precursor sequence for the assemblage now classed as "older gneiss and schist." No basement is preserved, so the initial thickness is not known. 2. Emplacement and serpentinization of ultramafic plutons in the volcanic-sedimentary terrane, pos- sibly as part of an ophiolite-like assemblage. (This inference is based on the restriction of the larger bodies of ultramafic rock to the older sequence and to the need for a source for the many smaller diapiric bodies of ultramafic rock now found dispersed through the younger quartzofeldspathic gneiss and the Christensen Ranch Metasedimentary Suite.) 3. Continued deposition of supracrustal strata, prob- ably conformable but changing in character to more felsic volcanic rocks interbedded with potassium- rich pelite and arkose. This assemblage probably at- tained a thickness of at least several miles. 4. On the basis of the record emerging for Archean history elsewhere in southwestern Montana, it is postulated (though no direct evidence can be cited) that the felsic assemblage noted in (3) was converted by metamorphism and magmatic additions to a sheet of quartzofeldspathic gneiss of regional dimensions, prior to deposition of the strata of the Christensen Ranch Metasedimentary Suite. This postulated event has yet to be dated by isotope geochronology. 5. Deposition of the strata now represented by the Christensen Ranch Metasedimentary Suite in a shallow marine environment on a basement of quartzofeldspathic gneiss. The basal beds probably were arkosic and subsequently converted to granitic gneiss not now distinguishable from the basement gneiss. These strata were overlain by dolomite, probably as a sheet of variable thickness but of regional extent, which was succeeded by a varied sequence of shale, dolomitic sandstone and shale, sandstone, and iron-formation that probably con- tained one or more repetitions of dolomite of more local distribution. 6. Uplift and low-angle deformation of the sedimen- tary pile, possibly by gravity sliding, including development of recumbent folds and of detachment surfaces, particularly at the base of the sedimentary sequence and at boundaries of thicker homogeneous lithologic units (such as dolomite marble) within the pile, and probable formation of one or more nappes. Original stratigraphic relations within the sedimen- tary sequence were extensively distorted and in places reversed. 7. Deep burial of the sedimentary terrane, followed by widespread intrusion of mafic magma, mostly as sills of diabase and gabbro. 8. Onset of the thermo-tectonic cycle that culminated about 2,750 m.y. ago. This orogenic event, or series of events, contained as a minimum the following elements (oldest to youngest): a. Intense compressional deformation on northeast- trending axes, to form northwest-dipping isoclines in all rock units, including the quartzofeldspathic gneiss. Ultramafic rock derived from initial sites in the "older gneiss and schist" unit was redistrib- uted as diapiric pods and lenses in the quartzo- feldspathic gneiss and overlying metasedimentary rocks. Some bodies of mafic rock also were de- formed plastically, particularly along fold axes. The folding was accompanied, probably contempo- raneously, by metamorphism of all strata to amphibolite facies, and by generation and local emplacement of granitic magma. Parts of the older quartzofeldspathic gneiss probably were remobilized at this time. b. Crossfolding of the northeast-trending isoclines on north-trending axes, producing upright folds and the complex geometry now evident in areal distribution of lithologic units. c. Emplacement of "older"" pegmatite as unzoned bodies and sheets that transect the older folded strata. d. Local resumption of mafic magma intrusion. This epoch is represented certainly by only one dike in the mapped area, but it is well established in the northern Ruby Range and in the adjoining Tobac- co Root Mountains. e. - Remetamorphism of the entire area, again to am- phibolite facies. This late thermal event was not accompanied by significant deformation; the lone late diabase dike recognized, now altered to am- phibolite and moderately foliated, retains its straight cross-cutting form. This Archean record, tabulated above, has much in common with certain other areas of similar Precambrian rocks. A notable analogy exists between this area and, for example, the Adirondack Mountains of New York. Though younger by considerably more than a billion years, the Adirondack lithic assemblage is similar, con- taining marble, amphibolite, and various layered gneisses, as well as widespread deposits of talc. The structural history, like that inferred for the Ruby Range, involves early low-angle deformation, including formation of nappes, followed by formation of co-axial 24 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA folds that were subsequently deformed on one or more sets of crossfolds (McLelland and Isachsen, 1980). PROTEROZOIC The geologic record of the approximately 2 billion years of Precambrian time that followed the major orogeny of the Late Archean is extremely sparse. Isotopic evidence developed by Giletti (1966) documents a regional thermal rise in Precambrian terranes of southwestern Montana west of the Gallatin River about 1,650 m.y. ago. It is probable that this also marks the time of widespread retrograde metamorphism of older Precambrian rocks of the Ruby Range and the emplace- ment of tourmaline-bearing zoned pegmatites. The only other rock-forming events known during Proterozoic time were the emplacement of diabase dikes about 1,425 m.y. ago and the formation of tale deposits. This meager record of events is summed up as follows, oldest to youngest: 1. Following close of the Late Archean orogeny, the region remained structurally quiescent for approx- imately 1 billion years. 2. Sometime late in the Early Proterozoic and culminating about 1,650 m.y. ago, the rocks of the Ruby Range area were subjected to a general rise in temperature. This resulted in extensive retro- grade metamorphism and emplacement of scattered 'small bodies of pegmatite, generally zoned. No firm quantitative data are available to indicate the temperature-pressure conditions during this event. 3. Immediately preceding (and possibly in part con- temporaneous with) diabase dike intrusion at about 1,425 m.y., the Precambrian crystalline rocks were offset on steeply dipping northwest-trending faults. Movement was left lateral, individual horizontal displacements being as much as 1 mi. 4. Emplacement of diabase dikes, age about 1,425 m.y., in fractures clearly related structurally to the northwest-trending fault system. 5. For the remainder of Proterozoic time, the area re- mained structurally stable, probably as an upland bordering the site of deposition of the Belt Super- group and later Proterozoic strata to the north and northwest. Within the Ruby Range area, the only recognized events were incomplete metamorphism of the diabase dikes and the formation of talc deposits, neither of which can be dated precisely. PHANEROZOIC The post-Proterozoic history of southwestern Mon- tana is complex and has been ably documented in many studies (for example, Klepper, 1950; Scholten, 1968; Tysdal, 1976b; Ruppel, 1982) and will be reviewed only briefly here. At the beginning of Paleozoic time, the Ruby Range area was still an upland. By mid-Cambrian time, how- ever, the entire region was covered by a shallow marine sea that persisted, with some breaks, into Mesozoic time. In the vicinity of the present Ruby Range, Paleo- zoic strata accumulated to an aggregate thickness of about 5,000 ft (Tysdal, 1976b). In the northern part of the range, these strata are well preserved in down- dropped fault blocks (Tysdal, 19762), but they have been stripped completely from the crystalline basement in the southwestern Ruby Range. Sedimentation, in part in nonmarine continental basins of limited extent, continued through the Mesozoic and into Cenozoic time in much of south- western Montana. In the vicinity of the Ruby Range, Paleozoic strata are unconformably overlain by the con- glomeratic Beaverhead Group. This clastic deposit marks the early stages of uplift of basement blocks on newly formed northeast-trending faults. Continued movement on these faults and on rejuvenated northwest-trending faults produced intermontane basins, which became sites of accumulation for thick clastic deposits of Eocene and younger age. Uplift of basement blocks culminated, in a regional sense, in late Tertiary time (Ruppel, 1982). The final recorded structural event in the southwest- ern Ruby Range was movement on the rejuvenated Stone Creek fault and Carter Creek fault, which pro- duced a 600-ft vertical offset in a basalt flow of Pliocene age. The Sweetwater Basin, on the downdropped side of the fault, was later covered to a shallow depth with clastic materials; these deposits, together with the alluvium along some streams, constitute the youngest geologic materials in the area. MINERAL RESOURCES Although the prime objective of this field study is the description of the extent and geologic setting of the bedded iron deposits, the occurrence of other mineral resources in the map area will also be reviewed in sum- mary fashion. The only mineral resource being extracted as of 1987 is talc, but in the past many other types of deposits were explored or investigated: graphite, nickel, pegmatite minerals, corundum, asbestos, sillimanite, and base-metal sulfides. IRON As previously described, banded iron-formation was deposited in at least two and probably several strati- graphic levels in the initial sedimentary sequence that MINERAL RESOURCES 25 now makes up the Christensen Ranch Metasedimentary Suite. The principal deposits, however, are believed to represent a single stratigraphic unit that generally ranges in true thickness from about 40 ft to 100 ft. The major area of economic interest and possible develop- ment, known as the "Carter Creek deposit," is a fold belt approximately 2.5 mi long and several hundred feet wide between the Hoffman Gulch and Carter Creek faults, mainly in secs. 3, 9, and 10, T. 8 S., R. 7 W. Elsewhere, particularly in the structural block between the Carter Creek and Stone Creek faults, iron-formation probably at the same initial stratigraphic position can be traced continuously in belts several miles long, but these lack the structural duplication necessary to pro- duce volumes of iron-formation worthy of serious economic consideration. The distribution and structure of the iron-formation that makes up the Carter Creek deposit are shown in figure 6, which is based on the previously published detailed map of the area (James and Wier, 1972b). The general structure of this belt is that of an overturned sequence tightly compressed into a number of northeast- to east-trending, northwest- to north-dipping isoclines. In a few places, however, notably in sec. 9, the iron-formation is contained in open gentle folds that are approximately co-axial (but not co-planar) with the isoclines. The iron-formation is bounded on the north and north- west by stratigraphically lower mica schist and quartz- ite and on the south and southeast by a thin bed of mica schist that gives way to epidote-diopside-hornblende gneiss containing distinctive widely spaced thin layers or laminae of pink calcite marble. Both upper and lower contacts of the iron-formation are relatively abrupt, and there is little interbedding with rock above or below. This overturned stratigraphic succession-older mica schist and quartzite, iron-formation, and strati- graphically younger schist and gneiss-is well exposed in the NWWMNE% sec. 10 (see cross-section A-A', fig. 6). Physically and chemically, the iron-formation is amenable to treatment as a low-grade iron ore (taconite). Grain sizes are relatively coarse, generally in the range 0.1-1.0 mm, which permits separation of magnetite and specularite from gangue minerals without excessively fine grinding. Bulk chemistry is much like that of other Archean iron-formation of similar mineralogic facies and of the iron-formation of the Mesabi district of Min- nesota, as shown by comparative data in table 6. It dif- fers from most commercially processed taconite in the relatively high ratio of ferric to ferrous iron (nearly 3:1; table 2), reflected mineralogically by the presence of specularite in addition to magnetite and of riebeckite, the ferric-ferrous sodic amphibole. Also notable in the chemistry of the iron-formation of the Carter Creek deposit is the low content of manganese and the relatively high phosphorous. Beneficiation tests were run on bulk samples by the U.S. Bureau of Mines, using magnetic separation. The results on three runs, using ball-mill grinding (pre- sumably to -100 mesh) and wet magnetic separation, are summarized as follows (from Holmes and others, 1962, p. 10): Test number ........................... 1 2 3 Quantity, tons .......................... 22 84.1 72.7 Initial Fe content, percent ................ 31.5 31.9 31.9 Fe recovery, percent ..................... 88.1 85.9 84.0 Concentrate: Fe, percent ........................... 55.9 - 57.5 61.1 SiO,, percent ......................... 7.15 16.6 12.6 The concentrate assays compare unfavorably with those of pelletized concentrates now being used in iron and steel plants in the United States, which typically con- tain 63-64 percent Fe and about 5 percent Si0g. Addi- tional laboratory-scale tests on concentrate by the U.S. Bureau of Mines, involving regrinding to -325 mesh and reprocessing, resulted in a product containing 69.8 per- cent Fe, at 97.2 percent recovery. In appraising the results of these beneficiation tests, it is to be noted that specularite, a significant constituent in some parts of the iron-formation, cannot generally be recovered by magnetic methods alone. Exploration of the Carter Creek deposit, which had been known to geologists since 1948 (Heinrich, 1960), began in 1956 (DeMunck, 1956) and has continued in- termittently since that time. Most of it has been done under the auspices of the Minerals Engineering Com- pany, and (later) Steel Alberta, Ltd., of Canada. Early churn drilling and trenching was followed by core drill- ing. Information on the amount of core drilling done is incomplete, but it is known to be in excess of 10,000 ft in aggregate. Locations of trenches and of diamond drill holes sunk in the late 1950's are shown on the previously published detailed map of the area (James and Wier, 1972b). Informal appraisals of reserve tonnage have been made by a number of investigators; estimates range from a few tens of millions to several hundred million tons. On the basis of surface area of exposure and pro- jection to a depth of 300 ft (a possible practical limit for open-pit mining), the resources of potential low- grade ore in the Carter Creek deposit, excluding that contained in isolated minor synclines, are here esti- mated to be about 95 million long tons, containing 28-29 percent recoverable (that is, nonsilicate) iron. Of this, slightly less than two-thirds is in Beaverhead County and slightly more than one-third is in Madison County. 26 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA 7000 P- 20 L LL z g 6500 413 i 9|10 $ & =i 35 i 8|3 (el 6000 g/O o| & £8 58 7000 e G L LL am . © > Z 6500 o ’— < Fx LJ zd LJ FIGURE 6.-Geologic map of the Carter Creek iron deposit, Madison and Beaverhead Counties, Mont. Map covers secs. 3, 9, and 10, T. 8 S., R. 7 W. MINERAL RESOURCES 27 Beaverhead County w|p 2G O Madison County 70 / e EXPLANATION [See plate 1 for descriptions and age relations of rock units] Diabase (Proterozoic) Center Pegmatite (Proterozoic(?) and Archean) sec. 10 F Amphibolite (Archean) Iron-formation (Archean) Strata enclosing iron-formation-Sequence is over- turned, so strata bounding main belt of iron-formation on north and northwest are older, those on south and s southeast are younger )/ 6 Contact / Fault 65 -- Strike and dip of layering in metasedimentary is rocks -a- Strike and dip of foliation 20 f soo 1000 1500 2000 FEET p Minor fold—Showing form in plan view, and bearing | | | | | and plunge of axis | I I | I I -»20 Bearing and plunge of lineation-May be combined 0 100 200 300 400 500 METERS with strike and dip symbol 28 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA TABLE 6.-Chemistry of the iron-formation of the Carter Creek deposit, southwestern Ruby Range, Mont., compared with other iron- formations 1 2 3 $10, 50 . 04 49.07 50.62 Fe (total) 31.77 31.65 30 . 84 Mn 0.04 0.42 0.46 P;O5 .36 16 . 09 Sample data: 1. Iron-formation of the Carter Creek deposit. Average of analyses 1-4, table 2. 2. Archean iron-formation of the Yilgarn block, western Australia (Gole and Klein, 1981, p. 176). 3. Biwabik Iron-formation (Proterozoic), Mesabi district, Minnesota. Recalculated on an H,0-free and CO,-free basis from previously published data by Gole and Klein (1981, p. 176). TALC Talc seams, veinlets, and lenses occur in dolomite marble throughout the area, and deposits have been mined sporadically for more than 40 years. Locations of larger known deposits that have been explored or mined in the southern Ruby Range are shown in figure 7. The two most recently active mines in the region, the Treasure Chest mine and the Beaverhead mine, are just outside the area covered by the general geologic map (pl. 1). Details on individual deposits are given by Perry (1948), Okuma (1971), and Garihan (1973, 1974), and a comprehensive review of the occurrence and develop- ment of tale resources of southwestern Montana is pro- vided by Olson (1976). The talc of the area is cryptocrystalline, opaque to translucent, and generally white to pale green or olive gray. Contacts with the dolomitic host rock typically are sharp, and bodies tend to be elongate in the plane of bedding in the marble. Impurities generally are scarce, but small flakes of graphite, relict from the replaced marble, are common in a few deposits, and limonite derived from oxidation of pyrite is a minor additional deleterious constituent in some. Other associated minerals noted include serpentine (locally abundant), chlorite, quartz, and phlogopite. In a few deposits the host marble is coarsely recrystallized, but whether this coarsening of grain was penecontemporaneous R 8 W R7 W R 6 W o Treasure & [--------Chest 09,5}; “85 mine [FC & el m C. x 1 pillion a Sef | s £222 C- Beaverhead & \/mine o &. h e A rea of plate 1 C A * x 6 8 2. x x7 8 s § 0 9 ic x5} L, @ a *g CS a (0) "ext. & Swe. a & & | 10%, N f 3 s \ 0 2 4 6 miles 0 0 20 4 6 kilometers FiGurE 7.-Location of principal talc mines and prospects in the southern Ruby Range. 1, Treasure State; 2, Regal; 3, American Chemet; 4, Sweetwater; 5, Sauerbier; 6, Owens-McGovern; 7, Bozo Zobo; 8, Banning-Jones; 9, Smith-Dillon; 10, Crescent. with talc formation or whether it was formed earlier is not clear. Much of the tale that has been tested is of "steatite"' grade, specifications for which, according to Olson (1976), call for less than 1.5 percent CaO, less than 1.5 percent Fe,Os, less than 4.0 percent Al;,O;, and only minute quantities of other impurities. Analyses of selected samples are given in table 7. The lithologic control for localization of tale is ab- solute: all deposits are in dolomite marble. Structural control is less certain. Many of the larger deposits (for example, those at the Treasure State and Treasure Chest mines, the Beaverhead mine, the American Chemet prospect, and the main pit of the Sweetwater prospect) are in narrow bands of dolomite marble wholly enclosed in older quartzofeldspathic gneiss; locally, as at the Treasure State and Treasure Chest mines, vir- tually the entire marble unit has been replaced. Some of these marble bands are demonstrably synformal, as at the American Chemet and Sweetwater deposits; others may represent structurally emplaced tectonic slices. The Regal (Keystone) deposit, however, is in the axial zone of a synform of marble enclosed in schist, and MINERAL RESOURCES 29 TABLE 7.-Analyses of talc from deposits in the southwestern Ruby Range, Mont. [From compilation by Olson, 1976. tr, trace; n.r., not reported; <, less than] 1 2 3 4 5 $10, 62.25 62.06 61.78 57.72 60.40 Al1,03 0.27 0.50 0.57 1.13 1.91 FeqO3 £71 . 67 . 75 0.48 0.27 CaO <.05 <.05 <.05 1,34 . 80 MgO 31.13 31.12 31.06 30.72 30.81 K,0 .02 . O1 .02 tr . 14 Na,0 . 06 . 07 . 08 tr . 20 H20' .14 .18 17 n.r. nL. n,0+* 5.03 5.09 5.17 5.94 5.15 CO» . 00 . 00 . 00 n.r. n.r. Sample data: 1, 2, 3. Smith-Dillon mine. Analysis by Leonard Shapiro. 4. Keystone (Regal) mine. G. Osborne Laboratories, Analysis by Raymond Inc. 5. Treasure (Chest) mine. Analysis by Raymond G. Osborne Laboratories, Inc. the Smith-Dillon deposit is in marble near a structural footwall of quartzite and granite gneiss. Aside from the Regal deposit, most tale bodies of significant size are in marble close to, or along a contact with, a chemical- ly and structurally dissimilar rock type, such as quartzofeldspathic gneiss. Larger masses of marble, such as those occupying extensive tracts in the north- central part of the map area, are notably deficient in talc deposits. The process of tale formation in dolomite involves the introduction of SiO; and H,O and loss of CaO and CO,, presumably through the agency of hydrothermal fluids. The source of the fluids and the timing of the event re- main unclear. Some evidence of relative age is poten- tially available at the Regal mine, where the tale zone is crossed by an undeformed diabase dike of Middle Pro- terozoic age. The actual contacts are not exposed, however, so age relations are not now determinable. It is to be noted that dikes of this group, though struc- turally undisturbed, have been affected by retrograde metamorphism, typically resulting in formation of hydrated minerals such as chlorite. This alteration pro- vides evidence, therefore, for post-dike introduction of low-temperature aqueous solutions on a regional scale. In the absence of evidence to the contrary, it is here suggested that the tale deposits are an additional prod- uct of this epoch of regional retrograde metamorphism, which occurred in later (post-1,425 m.y.) Precambrian time. GRAPHITE Graphite, in the form of dispersed fine flakes, is a com- mon minor constituent of marble throughout the area, and it is present as an impurity in some of the replace- ment talc deposits. The graphite deposits that have been of economic interest, however, are entirely dif- ferent in character; these are monomineralic pods, lenses, irregular veins, and disseminations in quartzo- feldspathic gneiss and pegmatite, found in a belt several hundred feet wide that trends northeasterly through the N% sec. 31, T. 8 S., R. 7 W. into the SE% sec. 30 and the SW! sec. 29 of the same township. Deposits in this belt, where graphite was first discovered in 1899, were mined intermittently from 1902 to 1945. They have been described in a number of geologic reports (Winchell, 1910, 1911, 1914; Bastin, 1912; Perry, 1948; Ford, 1954, and Heinrich, 1960), and the Crystal Graphite mine in sec. 31, T. 8 S., R. 7 W. has been mapped in detail (Arm- strong and Full, 1946; Armstrong, 1950). The principal deposits are in a zone that extends southwesterly from a tight infold of marble, a structure that trends N. 60 E. and plunges northerly at about 45°, with closure in the SE sec. 30, T. 8 S., R. 7 W. Lesser deposits occur on the south flank of the isoclinally in- folded marble. The graphite, locally bladed and in radiating clusters, forms discontinuous steeply dipping pods and seams that transect both quartzofeldspathic gneiss and Late Archean pegmatite. Individual bodies typically are less than 1 ft thick (average, about 4 in.) and are traceable laterally and vertically for distances rarely exceeding a few tens of feet. The Crystal Graphite mine exploited such deposits by means of a shaft and several adits, over a vertical range of about 340 ft. The Bird's Nest mine, from which the first graphite of the area was produced in 1902, is about 0.75 mi northeast of the Crystal Graphite mine; it is in gneiss and peg- matite on the south flank of the marble isocline. Devel- opment, all of which was done more than 80 years ago, was from three adits, the longest of which was driven about 270 ft. The origin of the deposits is somewhat problematical. They clearly are epigenetic, introduced into fractures in gneiss and pegmatite, the latter of Late Archean age. Ford (1954) concluded that the deposits were "epither- mal," a view properly rejected by Heinrich (1960), who suggested instead that the mineralization was a process that began ""in late pegmatite time." On the basis of isotopic analyses of the carbon, Weis and others (1981) 30 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA concluded that these deposits, like those of similar character but greater extent in Sri Lanka, originated by metamorphism and transfer of pre-existing syn- genetic graphite or carbonaceous detritus. Expressed in the usual per mil terminology-*°C content in parts per thousand, relative to the Peedee belemnite standard (12C/"3C = 88.99) taken as zero-Montana graphite (four samples) ranges from -4.9 to -6.1 per mil, and Sri Lanka graphite (three samples) has somewhat similar values, -8.0 to -8.6 per mil. These assays of *°C are con- siderably higher than those of reduced organic matter in rocks of lower metamorphic grade, which typically are in the range -20 to -25 per mil, and lower than that of marine carbonate, generally ranging between -1 and +2 per mil. Metamorphism of reduced organic matter is known, however, to result in *°C enrichment, and in fact Rumble and Hoering (1986) have shown that in some areas the *3C content of graphite spans virtually the entire range between that of reduced organic mat- ter and of marine carbonate. The process by which in- itial organic material is mobilized and redeposited as monomineralic pods and veins is not entirely clear. Weis and others (1981) suggest that the carbon is mobilized by the "water gas reaction," C+H,02CO+H;, trans- ported as carbon monoxide and precipitated by the "Boudouard reaction," 2CO-@-C+CO,. Rumble and Hoering (1986), noting the rarity of CO and H, in estimated compositions of metamorphic fluids, propose a more complex process, one involving interaction of COg-rich fluids derived from metamorphism of impure carbonate with CHy-rich fluids derived from organic matter. Graphite is precipitated when fluids of different CO,/CH, ratios are mixed, dominantly by the reaction CO, The isotopic composition of the precipitated carbon would vary widely according to the particular fluid mix and the prevailing temperature- pressure conditions. The argument presented by Rum- ble and Hoering (1986) is persuasive, but the conclusion remains speculative. Regardless of process details, how- ever, it can be concluded that the Montana deposits were formed by mobilization of carbon derived largely from what was originally organic detritus, followed by fluid transfer and redeposition as graphite under con- ditions of elevated temperature such as can be expected to have prevailed in the late stages of regional metamor- phism and magmatism in Late Archean time. OTHER MINERAL DEPOSITS As noted at the beginning of this section, deposits of a number of materials other than iron, tale, and graphite have been investigated for economic potential, generally without success. Most have been described by Heinrich (1960; also 1949a, 1949b, 1950a, 1950b), and they are reviewed briefly in the following paragraphs. NICKEL The local presence of annabergite, the nickel arsenate, as yellow-green crusts and fracture fillings in ultramafic rock exposed in the southeastern part of the map area led to staking of mineral claims and to some physical exploration (Sinkler, 1942). The explorations (located in sec. 31, T. 8 S., R. 6 W.; sec. 36, T. 8 S., R. 7 W.; secs. 1 and 2, T. 9 S., R. 7 W.; and sec. 6, T. 9 S., R. 6 W.) consisted mostly of shallow test pits but also included at least two holes drilled to depths of about 250 ft (Desmarais, 1978). The ultramafic rocks of the area are described in some detail by Heinrich (1963) and by Desmarais (1978, 1981). The economic significance of the supergene annaberg- ite is minimal. Olivine in the parent ultramafic rock does contain as much as 0.53 NiO (Desmarais, 1981), but this is within the normal range for olivine in alpine-type peridotite. CORUNDUM Corundum is found as a constituent of schist at two localities in the area. The principal deposit, discovered and described in some detail by Heinrich (1950b), is in sec. 36, T. 8 S., R. 8 W.; it consists of schist containing 5-35 percent corundum in an outcrop belt about 220 ft long and 20 ft wide and is not considered to have any economic value (Heinrich, 1960). The second deposit, in sec. 20, T. 8 S., R. 6 W., consists of scattered crystals of lilac-colored corundum (sapphire) in mica schist. The locality is immediately adjacent to the Sweetwater road and until fenced off in recent years was a favorite col- lecting site for amateur mineral collectors, who suc- ceeded in excavating a number of irregular pits in the weathered schist. The corundum deposits of the area are not unique in southwestern Montana. At least three localities have been explored as potential sources of corundum for abrasive uses (Clabaugh and Armstrong, 1951). The corundum-bearing rocks at these sites, as in the south- western Ruby Range, are within sequences of metasedi- mentary strata and probably owe their origin to high-grade metamorphism of alumina-rich shale. ASBESTOS At a number of places in the area, golden-yellow cross- fiber asbestos (chrysotile) is found as thin veinlets in altered dolomite marble adjacent to crosscutting diabase dikes of Middle Proterozoic age. Test pits, KELLY IRON DEPOSIT, NORTHEASTERN RUBY RANGE 31 notably in secs. 35 and 36, T. 7 S., R. 7 W., show the veinlets to be irregular, generally less than 1 in. wide, and rarely traceable for more than a few feet. None of the localities explored appears to have economic poten- tial. They are, however, remarkably similar in geologic occurrence to deposits that have been worked in the southern part of the Madison Valley, where chrysotile veins are in marble of the Cherry Creek Group at con- tacts with diabase (Heinrich and Rabbitt, 1960). PEGMATITE MINERALS Prospect pits have been sunk in many pegmatite bodies in the area, but the objectives of the testing are not always clear; some prospectors may have been at- tracted simply by the abundance of coarse quartz. All of the pegmatites contain quantities of feldspar, com- monly in coarse-grained masses, that in some circum- stances might have economic value, but a more likely economic target may have been muscovite mica, which in a few pegmatites is found as books as much as several inches in diameter. The quantity of mica in the explored pegmatites, however, is far too little to warrant con- sideration of further development. Rose quartz, com- mon in the core areas of zoned pegmatites, may also have been an exploration target, but again the quan- tities are economically insignificant. BASE METALS Throughout the area, prospectors have dug test pits and, in places, short adits and shafts on the basis of sur- face showings of secondary iron and copper minerals (limonite, hematite, malachite, azurite, and chrysocolla) and in a few places have uncovered sulfide-bearing materials. Most, but not all, mineralized rock is along structural breaks related to the northwest-trending fault system. Explorations are particularly common along the Stone Creek fault, where at least two short adits have intersected siliceous breccia containing disseminated pyrite and chalcopyrite. Test pits and a short inclined shaft in sec. 13, T. 7 S., R. 7 W. are located on easterly trending minor faults that cut the diopside gneiss bedrock; dump material consists of vein quartz and coarse carbonate containing chalcopyrite and bornite. Elsewhere in the area, exploration in the NW % sec. 1, T. 8 S., R. 7 W. has exposed a thin vein cutting layered schist and amphibolite; the vein strikes N. 45 W. and consists of disseminated bornite and chalcopy- rite in vuggy coarse-grained quartz. About 0.5 mi north- northwest of this locality, in the SW % sec. 36, T. 7 S., R. 7 W., dump materials from prospect pits in dolomite include vein quartz. Also present as coatings and fracture fillings in dolomite are malachite and an earthy pink mineral identified as erythrite (cobalt bloom); these minerals evidently are of supergene origin but the nature of the primary mineralization is not known. KELLY IRON DEPOSIT, NORTHEASTERN RUBY RANGE INTRODUCTION The Kelly iron deposit is on the northeast flank of the Ruby Range, 3-4 mi southwest of the town of Alder, and about 10 mi northeast of the southwestern Ruby Range map area. The locality, mostly in sec. 25, T. 6 S., R. 5 W., is at elevations between 6,000 and 7,000 ft. It is accessible from the adjacent Ruby Valley by way of an unimproved dirt road that follows Beatch Canyon and an access track, now largely impassable, that enters the area of exploration. Mining claims were staked in 1957 by John Kelly of Alder and subsequent- ly leased to the F and S Contracting Company of Butte. Exploration consisted of a number of deep trenches and cuts and two inclined diamond drill holes having an ag- gregate length of 1,142 ft. The topography and geology of the area were mapped by the U.S. Geological Survey in 1960 at a scale of 200 ft to 1 in. and surveyed with a tripod-mounted magnetometer (James and Wier, 1961). Later, a revised geologic map was published (James and Wier, 19722), on which the map in this report, plate 2, is largely based. GENERAL GEOLOGY Precambrian strata that contain iron-formation are exposed in a triangular area of a few square miles on the flank of the Ruby Range, bounded by strata of Paleozoic and Tertiary age. The western boundary of the Precambrian block is a high-angle fault of large displacement, which separates the Precambrian from limestone of the Madison Group of Mississippian age. The north margin is an unconformable contact with strata of Cambrian age. On the east, beyond the bound- ary of the map area, the Precambrian is bounded by downfaulted strata of Tertiary age. Most of the area covered by plate 2 is underlain by strata of the Christensen Ranch Metasedimentary Suite, here metamorphosed to granulite facies. These strata, in apparent normal stratigraphic order, are folded into an upright southeasterly plunging syncline, the buried axial part of which has been buckled and squeezed upward to form an anticlinal diapir-like struc- ture cored by a mass of ultramafic rock. The youngest 32 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA Precambrian rocks of the area are small bodies of microcline pegmatite of either Late Archean or Early Proterozoic(?) age, and at two localities bodies of moderately foliated quartz diorite of probable Early Proterozoic age. STRATA OF THE CHRISTENSEN RANCH METASEDIMENTARY SUITE These strata have been grouped for map display and text discussion into four principal units, as shown in figure 8. DOLOMITE MARBLE The dolomite marble that is the basal unit of the metasedimentary sequence has a minimum thickness of 400 ft. The marble is underlain by quartzofeldspathic gneiss, which though not exposed in the map area is abundantly present nearby (Karasevich, 1981). The loca- tion of the nearest contact suggests a possible thickness of marble in this area of 1,000 ft or more. Of the exposed section in the map area, the lower half is coarsely crystalline white dolomite marble, best displayed on the south-facing slope of Taylor Canyon below the Precambrian-Cambrian unconformity. The upper half is gray crystalline dolomite marble studded with greenish-yellow ovoids of serpentine. The ovoids, 0.5-3.5 mm in diameter, locally contain relict islands of forsterite in a matrix of antigorite. Blades of pale- brown phlogopite, generally heavily altered to talc, are common both adjacent to the serpentine ovoids and as separate flakes dispersed through the marble. Chemical analysis of the serpentine (forsterite) mar- ble, given in table 8, shows nearly equal amounts of MgO and CaO, testifying to the dolomitic composition of the initial carbonate. X-ray measurement on several samples reveals considerable range in present dolomite:calcite (43:57-100:0). GARNET QUARTZITE AND GNEISS The lower half of this 300-ft sequence is not well ex- posed but appears to consist mainly of micaceous quartzite and hornblende-diopside gneiss. The upper half consists of quartzitic strata containing distinctive layers of garnet-rich quartzite that grades into quartz- feldspar-garnet gneiss, locally including microcline-rich veins of pegmatitic aspect. The garnet, which comprises about 20 percent of some layers, is present as reddish- brown clusters of irregular outline. Chemical analysis of the garnet quartzite (see table 8) shows a relatively high content of FeQ, reflected mineralogically by the Map units Lithologic notes I | 2% /4 I ; MK Iron-formation Quartzite E (more than 265 feet) 3 BW Iron-formation 1 Vitreous quartzite Hornblende- diopside gneiss < (340 feet) Iron-formation | Vitreous quartzite *] Garnet-rich Garnet quartzite and gneiss _ 4 (300 feet) Dolomite containing ovoids of pases > serpentine Dolomite marble . (more than 400 feet) Coarsely crystalline ~2 Im FIGURE 8.-Stratigraphic section of the Christensen Ranch Meta- sedimentary Suite in the Kelly area, northeastern Ruby Range (thicknesses in parentheses). abundance of garnet and presence of magnetite as a common accessory. The rock can be assumed to have originated as an iron-rich feldspathic sandstone. KELLY IRON DEPOSIT, NORTHEASTERN RUBY RANGE 33 TABLE 8.-Chemical analyses of metasedimentary rocks from the Kelly area, northeastern Ruby Range, Mont. [In weight percent. Analyst, Paula M. Buschman] 1 2 $10, 8.50 70.41 FAPOA 0.91 12.00 Feq0q . 87 1.87 FeO .99 6.97 MgO 23.39 0.47 Cao 24 . 42 2.74 Na,0 .03 2.34 K,0 . 08 1.19 n,0+ 2.36 46 4,0~ .33 .05 TiO, .05 .86 P505 . 03 .19 Mno . 70 15 C0, 37.03 .23 Cl .07 .00 F .06 . O1 .00 . 00 € 07 02 Subtotal 99.89 99.96 Less 0 ___05 ___ 00 Total 99 . 84 99.96 Sample data: 1. Dolomite marble containing ovoids of serpentinized forsterite and blades of phlogopite. Sample HJ-194-60. 2. Garnetiferous quartzite, containing oligoclase, microcline, and magnetite; accessory sphene, apatite, and zircon. Sample HJ-187-60. HORNBLENDE-DIOPSIDE GNEISS The strata enclosing the main iron-formation of the area (described separately below) are composed mainly of dark, greenish-gray, streaky to poorly layered rock that typically consists of about 60 percent plagioclase, 20 percent hornblende, 15 percent diopside, and 5 per- cent quartz (fig. 94). The plagioclase generally is calcic andésine (Ange_49) but ranges from sodic andesine to calcic labradorite. The hornblende, black in hand specimen, is brownish green in thin section. The common pyroxene is greenish-gray diopside but in a few specimens it is hypersthene; no example of both pyroxenes occurring in the same sam- ple has been observed in the present study, but this association is reported by Dahl (1979). Other minerals present in varying abundance include garnet, biotite, microcline, and accessory magnetite and apatite. Scapolite was found in a few specimens but does not appear to be systematically distributed. A few thin beds of vitreous quartzite are interlayered with the gneiss. The most persistent of these is about 50 ft stratigraphically above the contact of the gneiss with the underlying garnetiferous unit; it is 10-20 ft thick. The aggregate thickness of the gneiss unit, including interbedded quartzite and iron-formation, is about 340 ft. The sedimentary assemblage now represented by hornblende-diopside gneiss can be assumed to have consisted initially of dolomitic muds containing vary- ing amounts of sand and clay. IRON-FORMATION The iron-formation of the area is heavy, dark rock composed principally of quartz, magnetite, and pyrox- ene; garnet is abundant in some layers but is absent in most. The rock tends to be streaky rather than distinct- ly layered; component minerals such as quartz are ag- gregated into flat lenticles a few millimeters in thickness and a few to tens of centimeters in length. The result- ant foliation is parallel to stratigraphic contacts, so doubtless is inherited from the thin layering typical of less metamorphosed iron-formations. Complex minor folding can be observed in nearly all outcrops; the general form of the folds tends to be systematic in rela- tion to major structures, but plunges commonly diverge. The stratigraphic thickness of the iron- formation contained within the gneiss unit is about 40 ft, but outcrop widths may be much greater because of structural duplication. Quartz and magnetite are the principal minerals, and grain sizes typically are 0.3 mm or more. Silicates make up 10-20 percent of most samples; dominant species are orthopyroxene and clinopyroxene in varying propor- tions (fig. 9B and C). Garnet, pink and isotropic in thin section, is abundant in a few layers but generally is ab- sent. Perthitic potassium feldspar is a common minor constituent, intergrown with quartz, and apatite occurs as small clear crystals. The two pyroxenes are similar in appearance in thin section: both are pale greenish to brownish gray, about 34 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA FIGURE 9 (above and facing page). -Photomicrographs of rocks from the Kelly area. A, Diopside-hornblende gneiss (specimen HJ-55-60); crossed polars. B, Quartz-rich iron-formation, con- taining hypersthene (specimen HJ-13-60); plane-polarized light. C, Silicate-rich iron-formation (specimen HJ-189-60); plane- polarized light. D, Metapyroxenite, containing relict hyper- sthene (specimen HJ-47-60); plane-polarized light. F, Peridotite (specimen HJ-15-60); relict olivine (high relief) in alteration matrix of antigorite plus magnetite; plane-polarized light. F, Quartz diorite (specimen HJ-52-60); plagioclase crystals commonly bent or fractured; crossed polars. Am, amphibole; Bi, biotite; Cpx, clino- pyroxene; Di, diopside; Hb, hornblende; Hy, hypersthene; Mt, magnetite; Pc, plagioclase (labradorite in A; oligoclase in F); Q, quartz. KELLY IRON DEPOSIT, NORTHEASTERN RUBY RANGE 35 equally birefringent, and very weakly pleochroic. The orthopyroxene is to be classed as hypersthene and the clinopyroxene, which consistently displays fine lamellae of exsolved hypersthene, is in the diopside-hedenbergite series. Locally, the pyroxenes are altered to complex assemblages that include blue-green hornblende, cummingtonite, brown mica, carbonate, and riebeckite. On the basis of paired compositions of clinopyroxene- orthopyroxene, garnet-orthopyroxene, garnet- clinopyroxene, and other mineral pairs, Karasevich and others (1981) estimate a peak temperature of metamor- phism of 745+50 °C, compared to 675+45 °C for the Carter Creek area of the southwestern Ruby Range. Chemical analyses of selected samples of iron- formation have been given earlier in this report (table 2, analyses 5, 6, and 7). The total iron content is strik- ingly consistent, but the amount present as magnetite is more variable, as indicated below: Analysis number (from table 2) .......... 5 6 7 Total Fe kkk} 37.33 37.59 37.27 "Excess" Fe, after assignment of all Fe,0, to magnetite |.... .....s. lg.. (fual. lily 7.34 3.16 3.72 Fe as magnetite ....................... 29.99 34.43 33.55 Standard commercial methods of iron determination commonly do not extract iron present in silicate minerals such as pyroxene and garnet, or else extract it incompletely, so that in commercial assays the iron content can be expected to agree more closely with that given above for iron in magnetite, rather than for total iron as determined by complete analysis. This is borne out by assay data available for drill core from the area, in which the average iron content reported is about 33 percent. Comparative aspects of the iron-formation chemistry have been discussed earlier in this report, in relation to the Carter Creek deposits. Of particular note are the relatively high values for Al;,O;, K,0, and MnO, and the distinctly lower content of P;O;. Physically and chemically the iron-formation is eminently acceptable as a taconite ore from which magnetite can be recovered after only moderately fine grinding. Quantitatively, however, the deposits lack the tonnage necessary for serious consideration as a can- didate for commercial exploitation. In the principal area of interest and exploration, the central upthrust block, the amount of iron-formation to a depth of 300 ft is estimated to be about 15 million tons, containing 33 per- cent recoverable iron. Elsewhere the iron-formation is in thin beds that offer virtually no prospect for development. QUARTZITE The uppermost packet of strata delineated on plate 2 consists of a sequence of quartzitic beds, individual units of which rarely exceed 20 ft in thickness, that enclose two or more thin beds of iron-formation. Biotite quartzite, biotite-garnet quartzite, and vitreous quartz- ite are well exposed in the eastern part of the map area, on the ridge immediately adjacent to the access track entering from Beatch Canyon. These rocks typically are 36 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA coarse grained, and biotitic varieties are strongly foliated. Some layers contain as much as 50 percent garnet, pink in thin section and isotropic. Trace amounts of sillimanite have been observed locally. Iron-formation, in beds generally 10 ft or less in thickness, occurs at several stratigraphic levels in the quartzitic sequence. Exposures are few, but the beds are readily traced magnetically. The rock is similar in almost all respects to the main iron-formation, described in earlier paragraphs. Quartz and magnetite are the principal minerals, and hypersthene, diopside- hedenbergite, and garnet are common constituents. IGNEOUS AND META-IGNEOUS ROCKS Four varieties of igneous or meta-igneous rocks are present in the Kelly area, but in the aggregate they con- stitute only a small fraction of bedrock. All are Precam- brian in age. ULTRAMAFIC ROCKS The principal mass of ultramafic rock in the area is a body of peridotite, arcuate in surface outline, that oc- cupies the core area of the central upthrust block con- taining the explored iron-formation. Metapyroxenite (not shown on plate 2; see James and Wier, 1972a, for locations) is present in a number of places as small lenses that, like the main mass of peridotite, have been tectonically emplaced, diapir-fashion, in the metasedi- mentary strata. The peridotite (or, more precisely, metaperidotite) is dense, dark gray to black on fresh break, weathering to the characteristic yellow-brown ("buckskin") surface typical of this rock type. It is complex mineralogically (fig. 96). Original pyrogenic minerals (olivine and pyrox- ene) are preserved as small islands in serpentine that is crossed by mesh-like trails of magnetite. The initial assemblage was coarse grained (grains 1-3 mm in diameter). The olivine is colorless in thin section and op- tically negative, showing an optic angle near 90°, in- dicating a magnesium-rich composition. The preserved pyroxene is augite, slightly brownish in thin section. Much of the rock now consists of tremolite, in large clear grains that replace both the original pyrogenic minerals and the late serpentine. Enstatite, similar in appearance to tremolite and probably also of metamorphic origin, is present in a few samples. Finally, these secondary minerals, together with the pyrogenic precursors, are in turn altered locally to cummingtonite, calcite, and serpentine. Metapyroxenite occurs as concordant thin lenses, most less than 20 ft thick and 100 ft long. The rock typically is medium to coarse grained and greenish black to black, depending upon the amount of second- ary hornblende present. The original rock appears to have been composed largely, if not entirely, of hyper- sthene, now preserved in small relict patches in an- tigorite serpentine. Both hypersthene and antigorite are replaced by a granoblastic aggregate of clear diopside and brown-green hornblende (fig. 9D). Locally, the rock in outcrop is a crumbly aggregate consisting largely of black coarse-grained hornblende. QUARTZ DIORITE Granitic intrusions are present at three localities in the map area, the most extensive near the center of sec. 25, T. 6 S., R. 5 W. The full extent of the latter body is not known, but it is at least 400 ft by 500 ft in sur- face area. A smaller body, in the NW sec. 25, is in exposed contact with diopside-hornblende gneiss, which near the contact is seamed with irregular pegma- titic veins. Most of the sampled granitic rock is quartz diorite that is fine to medium grained and gray to pink. In out- crop the rock is seen to be weakly to moderately foliated, and in thin section bending and fracturing of feldspar grains is evident. Typical samples consist main- ly of quartz and oligoclase (fig. 9F), with minor potassium feldspar (vaguely mottled and probably microperthitic) and biotite. The quartz diorite clearly post-dates the metamor- phism and main structural deformation of the metasedi- mentary sequence. Preliminary isotopic measurements of Rb/Sr of samples from the body in the NW 4 NW !H sec. 25, coupled with those from the nearby Virginia City area, yield an 1,890 m.y. isochron (C.E. Hedge, written commun., 1981), with a high initial ratio of about 0.719. PEGMATITE Pegmatite occurs throughout the Kelly area in bodies ranging from thin irregular seams to masses several hundred feet long and 100 ft wide. Most are of simple composition-pink microcline and quartz; in some smaller bodies the feldspar is white albite. Biotite and muscovite are common constituents of thinner lenses and seams but are scarce or absent in larger bodies. No rare minerals have been observed and the pegmatites are not zoned. Some larger bodies are moderately foliated but smaller veins and dikes are undistorted. The relation between the pegmatite and the quartz diorite is not known, but the structural similarity sug- gests a common time of emplacement, probably during the Early Proterozoic. REFERENCES CITED 37 STRATA OF PALEOZOIC AGE As noted previously, the Precambrian rocks of the area are bounded on the north and west by strata of Paleozoic age. The north boundary is an unconformity; here the Precambrian is overlain by the Flathead Sand- stone, locally glauconitic, which is succeeded by the Wolsey Shale, both of Cambrian age. On the west the Precambrian is in fault contact with massive limestone of the Mississippian Madison Group. These strata are described in more detail by Tysdal (1976b). STRUCTURE The principal structural elements of the area consist of Precambrian folds and faults within the block of crystalline rocks and faults that displace both Precam- brian rocks and the younger strata of Paleozoic age. The latter will be described first. POST-PALEOZOIC FAULTS The northern Ruby Range is crossed by a number of northwest-trending faults of major displacement (Tysdal, 1976a; Karasevich, 1981). Within the Kelly area, this system is represented by the fault that brings limestone of the Madison Group into juxtaposition with Precambrian crystalline rocks. This structure, labeled the "Kephart fault" by Karasevich, is not here exposed, but judging from the relation of the surface trace to topography, it dips steeply to the east. Movement is high angle and reverse, and the minimum displacement is several thousand feet. The Kephart fault in turn is cut by a later east-trending fault that is the structural control for the north branch of Taylor Canyon. Move- ment on this fault is dominantly left lateral, displacing the Kephart fault trace by about 800 ft, but offset of the Cambrian-Precambrian unconformity indicates some vertical movement, north side down. Poor ex- posures of the fault, about 900 ft north of the NVA cor. sec. 25, indicate a nearly vertical dip. PRECAMBRIAN STRUCTURES The major Precambrian structures of the area are a broad open syncline that is clearly outlined by the stratigraphically lower beds of the Christensen Ranch Metasedimentary Suite, and an upthrust central block that contains the explored iron deposits. The axial plane of the major syncline apparently is about vertical; the fold axis trends N. 70° W. and the plunge is to the east- southeast at about 40°. Minor structures, most inferred from map patterns and the located traces of magnetic units, are dragfolds that are systematic with respect to the major fold. The central fault block is a lens-shaped mass about 3,500 ft long and 1,200 ft in maximum width that has been thrust up from the keel of the main syncline. This mass, cored by peridotite, has the internal form of an east-southeasterly plunging anticline flanked by a pair of truncated synclines; almost certainly it originated as an anticlinal buckle in the deeply buried axial zone of the main syncline, moving upward from its original matrix like a squeezed watermelon seed. The iron- formation within the upthrust mass has been greatly thickened by complex folding, evident in most outcrops. The fault that bounds the central block on the north is exposed in an exploration trench about 700 ft south of the N% cor. sec. 25; it is a steeply dipping shear zone about 100 ft wide marked by intensely crumpled rock and thin quartz veins. The companion fault that forms the south boundary is not exposed, but its location is tightly controlled by stratigraphic data. These two bounding faults necessarily must terminate to the west, because they do not cut the stratigraphic units that outline the main syncline. A similar termination by merging is inferred for the eastern extension of the faults, but the evidence is not definitive. REFERENCES CITED Armstrong, F.C., 1950, Geologic maps of Crystal graphite mine, Beaverhead County, Montana: U.S. Geological Survey Press Release July 31, 1950. Armstrong, F.C., and Full, R.P., 1946, Geology and ore deposits of the Crystal graphite mine: U.S. Geological Survey Preliminary Report, February 1946. Bastin, E.S., 1912, The graphite deposits of Ceylon and a similar graphite deposit near Dillon, Montana: Economic Geology, v. 7, p. 419-443. Bayley, R.W., and James, H.L., 1973, Precambrian iron-formations of the United States: Economic Geology, v. 68, p. 934-959. Bielak, J., 1978, The origin of Cherry Creek amphibolites from the Winnipeg Creek area of the Ruby Range, southwestern Montana: Missoula, University of Montana, M.S. thesis, 46 p. Burger, H.R., III, 1967, Bedrock geology of the Sheridan district, Madison County, Montana: Montana Bureau of Mines and Geology Memoir 44, 22 p. Clabaugh, S.E., and Armstrong, F.C., 1951, Corundum deposits of Gallatin and Madison Counties, Montana: U.S. Geological Survey Bulletin 969-B, p. 29-53. Cordua, W.S., 1973, Precambrian geology of the southern Tobacco Root Mountains, Madison County, Montana: Bloomington, In- diana University, Ph.D. dissertation, 300 p. Dahl, P.S., 1977, The mineralogy and petrology of Precambrian metamorphic rocks from the Ruby Mountains, southwestern Mon- tana: Bloomington, Indiana University, Ph.D. dissertation, 280 p. 1979, Comparative geothermometry based on major-element and oxygen isotope distributions in Precambrian metamorphic rocks from southwestern Montana: American Mineralogist, v. 64, p. 1280-1293. 38 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA 1980, The thermal-compositional dependence of Fe**-Mg distributions between coexisting garnet and pyroxene Applications to geothermometry: American Mineralogist, v. 65, p. 854-866. Dahl, P.S., and Friberg, L. M., 1980, The occurrence and chemistry of epidote-clinozoisites in mafic gneisses from the Ruby Range, southwestern Montana: University of Wyoming Contributions to Geology, v. 18, no. 2, p. 77-82. DeMunck, V.C., 1956, Iron deposits in Montana: Montana Bureau of Mines and Geology Information Circular 13, 55 p. Desmarais, N.R., 1978, Structural and petrologic study of Precam- brian ultramafic rocks, Ruby Range, southwestern Montana: Missoula, University of Montana, M.S. thesis, 88 p. 1981, Metamorphosed Precambrian ultramafic rocks in the Ruby Range, Montana: Precambrian Research, v. 16, p. 67-101. Erslev, E.A., 1983, Pre-Beltian geology of the southern Madison Range, southwestern Montana: Montana Bureau of Mines and Geology Memoir 55, 26 p. Ford, R.B., 1954, Occurrence and origin of the graphite deposits near Dillon, Montana: Economic Geology, v. 49, p. 31-43. Garihan, J.M., 1973, Geology and tale deposits of the central Ruby Range, Madison County, Montana: Pennsylvania State Univer- sity, Ph.D. dissertation, 209 p. _____1974, Geologic road log from Dillon to Alder, covering the Precambrian geology of the central Ruby Range, southwestern Montana: Montana Bureau of Mines and Geology Special Publica- tion 13, p. 15-26. 1979a, Geology and structure of the central Ruby Range, Madison County, Montana-Summary: Geological Society of America Bulletin, Part I, v. 90, no. 4, p. 323-326. 1979b, Geology and structure of the central Ruby Range, Madison County, Montana: Geological Society of America Bulletin, Part II, v. 90, p. 695-788. Garihan, J.M., and Okuma, A.F., 1974, Field evidence suggesting a non-igneous origin for the Dillon quartzo-feldspathic gneiss, Ruby Range, southwestern Montana: Geological Society of America Abstracts with Programs, v. 6, p. 510. Garihan, J.M., and Williams, K., 1976, Petrography, modal analyses, and origin of Dillon quartzo-feldspathic and pre-Cherry Creek gneisses, Ruby Range, southwestern Montana: Northwest Geology, v. 5, p. 42-49. Giletti, B.J., 1966, Isotopic ages from southwestern Montana: Jour- nal of Geophysical Research, v. 71, p. 4029-4036. Gole, M.J., and Klein, Cornelis, 1981, Banded iron-formation through much of Precambrian time: Journal of Geology, v. 89, p. 169-183. Gulbrandsen, R.A., 1960, A method of X-ray analysis for determin- ing the ratio of calcite to dolomite in mineral mixtures: U.S. Geo- logical Survey Bulletin 1111-D, p. 147-152. Hadley, J.B., 1969, Geologic map of the Cameron quadrangle, Madison County, Montana: U.S. Geological Survey Geologic Quadrangle Map GQ-813, scale 1:62,500. Heinrich, E.W., 1948, Deposits of the sillimanite group of minerals south of Ennis, Madison County, with notes on other occurrences in Montana: Montana Bureau of Mines and Geology Miscellaneous Contribution 10, 21 p. 1949a, Pegmatite mineral deposits in Montana: Montana Bureau of Mines and Geology Memoir 28, 56 p. 1949b, Pegmatites of Montana: Economic Geology, v. 44, p. 307-335. 1950a, Sillimanite deposits of the Dillon region, Montana: Mon- tana Bureau of Mines and Geology Memoir 30, 43 p. 1950b, The Camp Creek corundum deposit: Montana Bureau of Mines and Geology Miscellaneous Contributions 11, 20 p. ______1953, Pre-Beltian geologic history of Montana [abs.]: Geological Society of America Bulletin, v. 64, no. 12, p. 1432. 1960, Pre-Beltian geology of the Cherry Creek and Ruby Moun- tains areas, southwestern Montana-Part 2, Geology of the Ruby Mountains: Montana Bureau of Mines and Geology Memoir 38, p. 15-40. 1963, Paragenesis of clinohumite and associated minerals from Wolf Creek, Montana: American Mineralogist, v. 48, p. 597-613. 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James, H.L., and Hedge, C.E., 1980, Age of the basement rocks of southwest Montana: Geological Society of America Bulletin, Part I, v. 91, no. 1, p. 11-15. James, H.L., and Wier, K.L., 1961, Geologic, topographic, and magnetic maps of the Carter Creek and Kelly iron deposits, Mon- tana: U.S. Geological Survey Open-File Report, scale 1:2,400. 1962, Magnetic and geologic map of iron deposits near Copper Mountain, Madison County, Montana: U.S. Geological Survey Open-File Report, 2 sheets, scale 1:2,400. 1972a, Geologic map of the Kelly iron deposit, sec. 25, T. 6 S., R. 5 W., Madison County, Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-349, scale 1:2,400. _____1972b, Geologic map of the Carter Creek iron deposit: U.S. Geological Survey Miscellaneous Field Studies Map MF-359, scale 1:3,600. James, H.L., Wier, K.L., and Shaw, K. W., 1969, Map showing lithology of Precambrian rocks in the Christensen Ranch and adjacent quadrangles, Madison and Beaverhead Counties, Montana: U.S. Geological Survey Open-File Map. Karasevich, L.P., 1980, Structure of the pre-Beltian metamorphic rocks of the northern Ruby Range, southwestern Montana: Pennsyl- vania State University, M.S. thesis, 172 p. 1981, Geologic map of the northern Ruby Range, Madison Coun- ty, Montana: Montana Bureau of Mines and Geology Geologic Map Series GM-25. Karasevich, L.P., Garihan, J.M., Dahl, P.S., and Okuma, A.F., 1981, Summary of Precambrian metamorphic and structural history, Ruby Range, southwest Montana: Montana Geological Society 1981 Field Conference Guidebook, p. 225-237. Klepper, M.R., 1950, A geologic reconnaissance of parts of Beaverhead and Madison Counties, Montana: U.S. Geological Survey Bulletin 969-C, p. 55-84. Marvin, R.F., Wier, K.L., Mehnert, H.H., and Merritt, V.M., 1974, K-Ar ages of selected Tertiary rocks in southwestern Montana: Isochron/West, no. 10, p. 17-20. McLelland, James, and Isachsen, ¥ngvar, 1980, Structural synthesis of the southern and central Adirondacks-A model for the Adiron- dacks as a whole and plate-tectonic interpretations-Summary: Geological Society of America Bulletin, Part I, v. 91, no. 2, p. 68-72. Miyashiro, A., 1973, Metamorphism and metamorphic belts: London, George Allen and Unwin, Ltd., 492 p. Mueller, P.A., Wooden, J.L., Henry, D.J., and Bowes, D.R., 1985, REFERENCES CITED 39 Archean crustal evolution of the eastern Beartooth Mountains, Montana and Wyoming, in Czamanske, G.K., and Zientek, M.L., eds., The Stillwater Complex, Montana-Geology and guide: Mon- tana Bureau of Mines and Geology Special Publication 92, p. 9-20. 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Poldevaart, Arie, 1955, Chemistry of the Earth's Crust, in Poldevaart, Arie, ed., Crust of the Earth: Geological Society of America Special Paper 62, p. 119-144. Rabbitt, J.C., 1948, A new study of the anthophyllite series: American Mineralogist, v. 33, p. 263-323. Reid, R.R., 1957, Bedrock geology of the north end of the Tobacco Root Mountains, Madison County, Montana: Montana Bureau of Mines and Geology Memoir 36, 25 p. Reid, R.R., McMannis, W.J., and Palmquist, J.C., 1975, Precambrian geology of the North Snowy block, Beartooth Mountains, Mon- tana: Geological Society of America Special Paper 157, 135 p. Ross, Malcom, Papike, J.J., and Shaw, K.W., 1969, Exsolution tex- tures in amphiboles as indicators of subsolidus thermal histories: Mineralogical Society of America Special Publication No. 2, p. 275-299. Royse, C.F., Jr., Wadell, J.S., and Peterson, LE., 1971, X-ray deter- mination of calcite-dolomite-An evaluation: Journal of Sedimen- tary Petrology, v. 41, no. 2, p. 483-488. Rumble, Douglas, and Hoering, T.C., 1986, Carbon isotope geochem- istry of graphite vein deposits from New Hampshire, U.S.A.: Geochimica et Cosmochimica Acta, v. 50, p. 1239-1247. Runner, J.J., and Thomas, L.C., 1928, Stratigraphic relations of the Cherry Creek group in the Madison Valley, Montana [abs.]: Geological Society of America Bulletin, v. 39, p. 202-203. Ruppel, E.T., 1982, Cenozoic block uplifts in east-central Idaho and southwest Montana: U.S. Geological Survey Professional Paper 1224, 24 p. Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1983, Preliminary geologic map of the Dillon 1°X2° quadrangle, Montana: U.S. Geological Survey Open-File Report 83-168, scale 1:250,000. Sahinen, V. M., 1939, Geology and ore deposits of the Rochester and adjacent mining districts, Madison County, Montana: Montana Bureau of Mines and Geology Memoir 19, 53 p. Scholten, Robert, 1968, Model for evolution of Rocky Mountains east of Idaho batholith: Tectonophysics, v. 16, no. 2, p. 109-126. Sinkler, Helen, 1942, Geology and ore deposits of the Dillon nickel prospect, southwestern Montana: Economic Geology, v. 37, p. 136-152. Tansley, Wilfred, Schafer, F.A., and Hart, LH., 1933, A geological reconnaissance of the Tobacco Root Mountains, Madison Coun- ty, Montana: Montana Bureau of Mines and Geology Memoir 9, 57 p. Tysdal, R.G., 1976a, Geologic map of the northern part of the Ruby Range, Madison County, Montana: U.S. Geological Survey Miscel- laneous Investigations Series Map I-951, scale 1:24,000. 1976b, Paleozoic and Mesozoic stratigraphy of the northern part of the Ruby Range, southwestern Montana: U.S. Geological Survey Bulletin 1405-I, p. 11-125. Vitaliano, C.J., Cordua, W.S., Burger, H.R., Hanley, T.B., Hess, D.F., and Root, F.K., 1979, Geology and structure of the southern part of the Tobacco Root Mountains, southwestern Montana-Map summary: Geological Society of America Bulletin, v. 90, pt. 1, no. 8, p. 712-715. Weis, P.L., Friedman, Irving, and Gleason, J.D., 1981, The origin of epigenetic graphite-Evidence from isotopes: Geochimica et Cosmochimica Acta, v. 45, p. 2325-2332. Wier, K.L., 1965, Preliminary geologic map of the Black Butte iron deposit, Madison County, Montana: U.S. Geological Survey Open- File Report, scale 1:9,600. 1982, Maps showing geology and outcrops of part of the Virginia City and Alder quadrangles, Madison County, Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-1490, scale 1:12,000. Winchell, A.N., 1910, Graphite near Dillon, Montana: U.S. Geological Survey Bulletin 470, p. 528-532. ______1911, A theory for the origin of graphite as exemplified in the graphite deposit near Dillon, Montana: Economic Geology, v. 6, p. 218-230. 1914, Mining districts of the Dillon quadrangle, Montana, and adjacent areas: U.S. Geological Survey Bulletin 574, 191 p. Wooden, J.L., Vitaliano, C.J., Koehler, S.W., and Ragland, P.C., 1978, The late Precambrian mafic dikes in the southern Tobacco Root Mountains, Montana-Geochemistry, Rb-Sr geochronology, and relationship to Belt tectonics: Canadian Journal of Earth Sciences, v. 15, p. 467-479. v U.S. GOVERNMENT PRINTING OFFICE: 1989-773-047/06019 i E672 &% k [a S be ina» . Quebw’kswe ‘ ub t M] i 1 1990 Topographlc and Structural Conditlons in Areas of Gravitational Spreading of ‘ Ridges in the Western United States U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1496 EARL a; DEPOSITQRV DEC 0 7 199g AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur- rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." 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SAVAGE U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1496 A study relating gravitational spreading of ridges to local topography and geologic structure UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1989 DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Varnes, David J. (David Joseph), 1919- Topographic and structural conditions in areas of gravitational spreading of ridges in the western United States. (U.S. Geological Survey professional paper ; 1496) Bibliography: p. Supt. of Docs. no.: I 19.16:1496 1. Rifts (Geology)-West (U.S.) 2. Geology, Structural. I. Radbruch-Hall, Dorothy H., 1920- ._ II. Savage, William Z. III. Title IV. Series. QE6O6.V36 - 1989 551.8'0978 88-600430 CONTENTS Page ADStrACK |.. . ..o. ; .s cscs ss c vis vv oie dee salvar ra kk aas 1 | Stillwater Complex, Montana ......................... Introduction |... ...es 1 | Relation of sackungen to topography and rock structure .. Localities in the Sawatch Range, Colorado .............. 3 T I eld Eagle Mounts o Mount Mace! s 'opography ll.... .age .oun am att Ount MBBBIVE .~ : « +c ( 36. Aerial oblique view of an area southeast of Busk Creek and southwest of the tributary valley that forms the southwestern border of the well-developed sackung trenches ............................. Stereopair of vertical aerial photographs showing area of intricate pattern of shallow trenches above the prominent bench and scarp on the southeast side of Busk Creek valley kkk} 00s Index map of the State of Washington .sk kerr reek kk kkk kn n n k k k krn n reek ees Conformal transformation for a symmetric ridge in x,y coordinates to a half-plane in u,v coordinates ...... ... Contour plots of stresses in a symmetric ridge seker erea kk k kn n k k kk nnn nere e> Diagrams showing predicted zones of potential failure in a symmetric ridge for zero pore-water pressure and angle of internal friction @=80°% lr kkk kk kkk 66k kk kk kkk k e k k kkk ann e kkk keene Sketch of the potential flow regions and predicted senses of shear on examples of rupture surfaces for a symmetric gravitating MIGge ........................ .k kkk kee kk e n e e a a a a a ee ee e e e a a e eee e e a a a a ee e a a a a ee es TABLE TABLE 1. Joint spacing at several localities in the Bald Eagle Mountain study area ..................................... Page 19 19 19 20 20 21 21 28 23 24 25 25 25 26 27 Page 10 TOPOGRAPHIC AND STRUCTURAL CONDITIONS IN AREAS OF GRAVITATIONAL SPREADING OF. RIDGES IN THE WESTERN UNITED STATES By D. J. VARNES, D. H. RADBRUCH-HALL, and W. Z. SAVAGE ABSTRACT Gravitational spreading of steep-sided ridges produces character- istic geomorphic forms including grabens and depressions along ridge crests, trenches, and uphill-facing, as well as downhill-facing scarps, on the mountain flanks, and outward bulging of the lower slopes. These sackung-type features occur in a variety of geologic settings in the Western United States. Those discussed here occur principally in high, linear ridges separated by glaciated valleys. The ridges are underlain by hard, but closely jointed, Precambrian igneous rocks. Topography is the primary determinant of the location and direction of the tren- ches and scarps, but the topographic grain of the terrane is, itself, determined in part by rock structures, such as joints and faults. In the Sawatch Range in Colorado, some valleys in the study area follow the direction of primary joint systems and, in turn, determine the direc- tion of trenches and scarps parallel to slope contours. The principal joint sets are, themselves, parallel to microcracks in the rocks. The relation of sackung features to structural elements is close in the Sawatch and Williams Fork Mountains in Colorado, not obvious at the one site examined in the Sangre de Cristo Mountains of New Mex- ico, close in the Stillwater Complex in Montana, and apparently close in a zone around the Straight Creek fault in the northern Cascade Mountains in Washington. Elastic-plastic stress analysis indicates that uphill-facing scarps may develop in the upper extending parts of a slope preferentially over downhill-facing scarps. INTRODUCTION Large-scale, deep-seated distortion of steep-sided ridges has come under increasing study both abroad and in the United States during the past 20 years. One im- petus for study of these features comes from the resemblance of their surface morphologic features, primarily scarps, to those of recent faults, and the need to identify and quantify fault movements and recurrence intervals for a variety of construction activities. Al- though the scarps observed are technically fault sur- faces, they result from the local adjustments within steep-sided ridges rather than far-field tectonic stresses. Making the distinction from tectonic faults is not always simple, for scarps due to local movement often follow pre-existing discontinuities in rock masses, including tectonic faults, joints, cleavage, schistosity, or foliation. Manuscript approved for publication September 14, 1988. The forms of sagging developed in the steep-sided slopes depend very much on the lithology of the masses involved, the degree of development of existing discon- tinuities, and the relation of the strike and dip of anisotropic elements to the direction and angle of dip of the slope. Three general lithologic settings may be distinguished: (1) massive, strong (although jointed) rocks lying on weak rocks; (2) ridges composed generally of metamorphosed rocks with pronounced foliation, schistosity, or cleavage; and (3) ridges composed of hard, but fractured, crystalline igneous rocks. Slope deformations in all these settings have been referred to by many authors, including ourselves, variously as "sackungen,"' from the German word for sagging, or by the term "deep-seated creep." As the name implies, these features can be shown to result from large-scale gravitational spreading (Radbruch-Hall and others, 1976; Savage and Varnes, 1987). The mode of origin is illustrated in this report in the section "Elastic-Plastic Stress Analysis of Gravitating Ridges." Sackungen of the first type, involving the spreading of rigid rocks overlying soft rocks, have been described previously (Radbruch-Hall, 1978). Gravitational spread- ing for this case was modeled by finite-element analysis (Radbruch-Hall and others, 1976). These kinds of move- ment are not discussed here. The second type shows features as described in detail by Zischinsky (1969) from the Austrian Tirol, and was referred to by him as "true Sackung.'" This involves much more extensive sagging and bending of foliated schists, phyllites, and gneisses than is found in more homogeneous and competent rocks. Our attention in the present report is directed mainly at sackungen of the third type, and we are concerned with mostly ridges above glacially oversteepened valleys in Precambrian granite and migmatite in cen- tral Colorado and to features in some other localities in the Western United States. The mechanics of gravita- tional spreading of such ridges of more or less homog- eneous crystalline rocks are not well understood. Hence, as part of the study of the origin of sackung features, 1 35° 2 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. we have considered their relation to topography and to local and regional structure. In 1977 and 1978, sites were visited at Bald Eagle Mountain, Surprise Ridge, and Mount Nast in the gran- ite and gneiss of the Sawatch Range in Colorado, and sites in layered basic igneous rocks of the Stillwater Complex in Montana were also visited (figs. 1, 2). Brief reconnaissances were made of parts of the Williams Fork Mountains of Colorado (fig. 2) and of the Cascade Moun- tains east of Seattle, Wash. In the Sawatch Range, the orientations of jointing and foliation were measured and oriented samples were taken, from which thin sections were made. In 1981, sackungen were examined in more detail in the Williams Fork Mountains, particularly near Ute Peak and Old Baldy, where jointing and foliation were measured. In 1982, additional observations were made at Mount Nast and Surprise Ridge, a large sackung was examined on Mount Massive, and others were in- vestigated in the Sangre de Cristo Mountains of New Mexico between Taos and the southern border of Col- orado (fig. 1, locality 5). Jointing and foliation were measured at each of these localities. 115° 110° 105° I I I ‘ - reso Z 7 MONTANA [ 45° |__ \ ______ 1 soUTH _ - 'we pl \ PIERREo TA |, BOISE | % IDAHO 1 I wYOMING *= I fame -- am as) 4 | - NEBRASKA 1 EYENNE NEVADAj |__ __E'___—LL————‘ OSALT LAKE 1 ag* |- CITY a 4>o<§2 _ DENVER \ UTAH COLORADO 1 NEW MEXICO | I I FE \\i ARIZONA | SANTA \ 1 | 1 0 300 MILES FIGURE 1.-Index map showing location of sites in the Rocky Moun- tains of the Western United States discussed in the text. (1) Stillwater Complex, Montana; (2) Williams Fork Mountains, Colorado; (3) Bald Eagle Mountain and Mount Massive, Colorado; (4) Mount Nast- Surprise Ridge, Colorado; (5) Site in the Sangre de Cristo Mountains, New Mexico. 106°30' 106°00° I f I 39°30° "° C * U Fairplay | R!d9® \, Mount Massive __________ 14,421 ft _\Area of =p figure 6 > Mount Elbert yp 14,433 ft £ 39°00 |- p #8. 0 10 20 MILES fem c cn il Lannon FIGURE 2.-Index map showing by dashed rectangles the location of study areas in the Williams Fork Mountains and Sawatch Range, Colorado. The sackungen we have studied have the following characteristics, not all of which may be developed at any one locality: f 1. Uphill-facing scarps on the slope, one to a few meters high, trending approximately parallel with topo- graphic contours and commonly somewhat convex downslope in plan. The trenches so produced are asymmetric in profile: The steep, upward-facing scarp is on the downhill side of the trench; the gentler, uphill side appears often to be an unmodified hillslope. 2. A graben or grabens along the ridge crest, commonly with closed contours and ephemeral ponds. . Double-crested ridges. . Bulging of the lower parts of the slopes. 5. Occurrence on the upper flanks of glaciated valleys, with the movement apparently being post-glacial. 6. Local relief more than 1,000 ft. 7. Occurrence more common on massive and often some- what rounded ridges, rather than on narrow ridges between cirques. Profiles across spreading ridges of type 3 are shown in figure 3. a Co LOCALITIES IN THE SAWATCH RANGE, COLORADO 3 B FIGURE 3.-Sketch of common profiles across spreading ridges in hard, jointed crystalline rocks (sackung, type 3). A, With ridge- top graben; B, With double-crested ridge. The lower parts of the originally glaciated valleys have been modified by bulging and the accumulated debris of talus and rock falls. Arrows indicate sense of relative displacement along fractures. LOCALITIES IN THE SAWATCH RANGE, COLORADO BALD EAGLE MOUNTAIN AND MOUNT MASSIVE A ridge-top graben and hillside trenches mark a ma- jor sackung feature on a broad ridge that extends southwestward from Bald Eagle Mountain, 9 mi west of Leadville, Colo. A mass of rock on the northwest side of the ridge has moved northwestward toward the valley of Busk Creek (figs. 4, 5). The geologic map of the Bald Eagle-Mount Massive area (eastern portion of fig. 6), indicates that the rock exposed is granitic (Yg), which, here, consists of gneiss cut by stringers and masses of granite and pegmatite rock. Figure 6 shows the sackung trenches on Bald Eagle Mountain, as well as joint and foliation attitudes. The graben and trenches trend approximately N. 50° E. Joints and foliation are locally well exposed in fresh rock in a cirque on the southeast side of the ridge, northeast of Rainbow Lake. The major joint set in the cirque trends N. 47-67° E. and dips 73-85° SE. (fig. 7). Foliation, as well as a secondary set of joints parallel to the foliation, trends approximately N. 45° W. and dips 30-40 ° NE. A prom- inent joint set at the north end of Bald Eagle Moun- tain strikes N. 17-20° E. and dips 42-64° NW. (fig. 6). Joint spacing is from less than 1 in. up to 6 ft, with most being spaced from 6 in. to 2 ft apart. Triangulation-trilateration nets established at Bald Eagle Mountain in 1975 and 1977 were remeasured in 1982 and extended in 1984. No movements in excess of expected surveying errors have been detected. A pronounced trench is visible on a cirque wall on the northwest slope of Mount Massive, about 3% mi south- west of the Bald Eagle sackung locality (fig. 6). Here, coarse-grained, somewhat foliated granitic rock is cut by well-developed joints from a few inches to more than 6 ft apart. A large and deep, northeast-facing cirque lies directly below and north of the highest point on Mount Massive. It is separated from a much shallower basin to the northwest by a narrow, northeast-trending ridge. A block of rock approximately 3,000 ft long and 200 ft wide has separated from the ridge and has moved down and out toward the large, steep-walled cirque to the southeast, forming a long, northeast-trending trench and uphill-facing scarp on the gentle, northwest-facing slope of the shallower basin northwest of the ridge (fig. 8). For much of its length, the face of the uphill- facing scarp consists of plane surfaces that are the walls of joints that trend N. 20-35° E. and dip 62-77° SE. This trend is somewhat more northerly than that of the Bald Eagle sackung trenches and that of the major joints in the cirque between Bald Eagle Mountain and Mount Massive. Other joints in the face of the uphill- facing scarp on Mount Massive trend N. 5-50° W. and dip 22-74° NE. In places, joints follow the foliation, which is variable. JOINT ATTITUDES Figure 9 shows the poles, plotted on a Wulff stereo- graphic net, of planes of joints and foliation in the Bald Eagle-Mount Massive area. There is a good deal of scatter of the joint directions and dip, particularly of the less well-developed joint sets. Foliation is generally not well developed here. A concentration of poles of the most prominent joint set is visible in the northwest and southeast quadrants of the diagram indicating a tenden- cy towards a northeast strike of the main joints. A con- centration in north-northeast strike is more easily seen in figure 10, in which the ares of intersection of planes on the lower hemisphere are plotted for the most prom- inent joint at each place of observation. Observations of principal joints at three places at the foot of a very steep slope below the lowermost trench in areas where bulging, dilation, and possible rotation of blocks is to be expected are plotted in figure 10 as dashed lines. 4 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. e" Q ‘ L -“!_ Z - - q # * ._, % Trenches < FIGURE 4.-Aerial oblique view looking northeastward down the valley of Busk Creek. On the broad southwest ridge of Bald Eagle Moun- tain to the right, a ridge top shallow graben and trenches high on the northwest slope are outlined by snow. Also marked by snow is a bench about halfway up the slope, trending parallel to the contours. We have not observed sackung-type trenches and scarps in essentially unjointed rock. Nor have we ob- served a shear surface cropping out at the base of a slope that has trenches and scarps. Thus, one of the requirements for a ridge of granitic rock to undergo creep movement appears to be that the rock mass is closely divided by joints so that relative displacements of a flow-like character can occur without the necessity of a through-going basal slip surface. To obtain some quantitative measure of the degree to which rock in the Bald Eagle Mountain area is divided, we measured the joint spacing in bedrock exposures and the size of loose blocks on the surface. JOINT SPACING The spacing of joints of in-place bedrock was meas- ured at several localities in the Bald Eagle area as shown in table 1. The spacing of joints having the orien- tation recordeu in column 2 of table 1 was measured on intersecting joints having the orientation shown in column 3. JOINT BLOCK SIZES Measurement of the longest, shortest, and intermediate dimensions were made of 100 randomly selected blocks lying loose along the low scarp on the northwest side of the shallow graben on the crest of the southwest ridge of Bald Eagle Mountain. The longest long dimension was 44 in., the median long dimension was about 11.5 in. The longest short dimension was 26 in. The median volume, assuming a rectangular prismatic shape, was 437 cubic in. Measurements of 25 blocks at triangulation station 3, just below the lowest trench, yielded roughly comparable results. The longest long dimension was 44 in., the longest short dimension was 16 in., and the median volume was approximately 1,200 cubic in., considerably larger than the median volume at the ridge top graben. The reason for this difference is unknown. MOUNT NAST AND SURPRISE RIDGE Sackungen are well developed in the Sawatch Range west of Bald Eagle Mountain, on Mount Nast, west of (Continued on p. 9) panasqo st d.reas ayy, 'snoju09 ay1 01 forfe.red ayq Suore spuajxa apts [[rydn sit 'ageurep yoo1q xsng oy} ojut premsea _ uo d.reos yjIm yousq quouruoid y sa10 adpu ayy reau uage18 ay1 pue yoo1;) ySng -Yjnos apTAIQ TejU@UuTju0;) ay} Jo apts jSom ay} WouJ 1972 uoj|re;) . Jo qseayjnos adojs ay, uo sayoua.1 Jo eare Surmoys 'eare urejunopy a[d2 ; au,, 'soypua.1 ay; mojoq adojs ay; ;o a8nq ayq yo A4jturota ay ut sqtsodap 4q - pjreg-yeo1q sng 943 JO syde1Sojoud jeorj19A wou; 1j9fdrn0a10}g-'g SHNOIY "% TINNNL NOLTYV3 TVL4Od $3391]. (eb "S d1e9s pug semen O A < p O A3 0 0 m [&] Z, < m a © a < - < w m asl E s w E - m md ») | -[! 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XC SU & (A 3 -C-, AL) ) = k +L Mrs tn 5, S Au Ue /‘;///’ 1/1” F | / - [ f | 3 S ( 4 + / y \)v\\\ < // "u /> CRB. 2a VA \ ill 1929 and pri \ R 77 W SANGRE DE CRISTO MOUNTAINS, NEW MEXICO 15 EXPLANATION Alluvium and stream gravels, bog deposits QUATERNARY ol Landslide deposits Non-glacial Qd Glacial drift surf|c1.al deposits Kp Pierre Shale undivided CRETACEOUS Ke Colorado Group-Niobrara Formation and Benton Shale Kd Dakota Sandstone EARLY xg Granitic rocks of PROTEROZOIC ~1700 m.y. age group Biotite gneiss and schist, migmatite Contact Fault-Dashed where approximately located, dotted where concealed. Bar and ball on downthrown side rone Thrust fault-Sawteeth on upper plate é;— Strike and dip of beds +k Strike and dip of foliation -a- Strike and dip of joint set -=- Vertical joint Linear feature of probable gravitational origin Scarp of gravitational origin-Teeth on downthrown side SCALE 1:62 500 Area of 1 V 0 1 MILE God's/2850 “VIII” e | ; | 1 5 0 1 KILOMETER CONTOUR INTERVAL 50 FEET LOCATION MAP NATIONAL GEODETIC VERTICAL DATUM OF 1929 <-FIGURE 20 (above and left).-Geologic map of the Ute Peak-Old Baldy study area, Williams Fork Mountains, Colorado, showing location of sackung-type features. Geology from Tweto (1973) and Tweto and Reed (1973b) with linear features and scarps of gravitational origin and some structural observations added by Varnes and Radbruch-Hall. FIGURE 21.-Aerial oblique view looking northward toward Ute Peak, which is the short ridge that rises above the general summit area in the right-central part of the photograph. The west side of the ridge summit has moved downward and westward. FIGURE 22.-Stereotriplet of the Ute Peak area showing a prominent southwestward-facing scarp northwest of Ute Peak on the east flank of the ridge, many scarps along the crest west of Ute Peak, and upward-facing scarps on the western slope. 16 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. FiGurE 23.-View northward toward the trench extending north- westward from Ute Peak, which is out of view on the right. The scarp on the eastern side of the trench is about 30 ft high. northwest of Ute Peak. FiGURE 24.-Upward-facing scarps on the convex slope west and FIGURE 25.-Aerial oblique view looking east-southeast over prominent trenches on the western side of the rounded crest of the Williams Fork Mountains, 1.8 mi south of Ute Peak. The animals on the crest of the highest scarp are elk. 17 SANGRE DE CRISTO MOUNTAINS, NEW MEXICO FiGurE 26.-Oblique aerial view looking north-northwest toward Old Baldy, showing trenches on the west side of the ridge crest; the larger trenches are outlined with snow. Poles Most prominent joint set o Second joint set Other sets, or all sets equally developed and plotted X Foliation; superposed on joint symbol if joint follows foliation F1GURE 27.-Plot of poles of joints and foliation observed in the Ute Peak-Ptarmigan Peak and Old Baldy areas of the Williams Fork Mountains. 18 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. STILLWATER COMPLEX, MONTANA In the Stillwater Complex, a large, basic, layered intrusive of Archean age in the Beartooth Mountains of Montana, sackungen have formed along the north- east side of the valley of the Boulder River, on the southwest side of a ridge known as Contact Mountain (Segerstrom and Carlson, 1982) (fig. 28). The main sackungen trenches and uphill-facing scarps strike approximately N. 65° W. and are about parallel to the slope contours (fig. 29). A major joint set parallels the layering, which strikes generally N. 60-65° W. and dips 50-60° NE. into the slope; another near-vertical set approximately normal to the layering strikes N. 30-35° E. (fig. 30). A graben lies at the crest of the ridge (fig. 31) and movement has taken place along both sets of joints to form the graben and trenches. Al- though the trenches are in bedrock, the ridges that bound them on the downhill side are capped in places by remnants of glacial till. Therefore, the sackung features formed after the glaciers that occupied the valley of Boulder River had retreated, which left the oversteepened slope unsupported. RELATION OF SACKUNGEN TO TOPOGRAPHY AND ROCK STRUCTURE TOPOGRAPHY The primary control on the location of spreadings ap- pears to be topographic; that is, the necessary relief to produce stresses sufficient to cause failure must be pre- sent, together with a sufficient length of free slope to allow their visible expression in shear surfaces. However, topography is not the sole determinant, for spreadings commonly are not continuous along ridges that have almost uniform shape and relief. Local and perhaps subtle variations in the spacing and orienta- tion of pre-existing discontinuities, as well as minor topographic features, may then fix the limits of the area affected. Although the relation of spreadings to topography is close, the orientation of ridges and the steepness of slopes of a mountainous area are themselves largely determined by the tectonic fabric of the region, as well as by factors that affected the accumulation of ice and distribution of glaciers during the Pleistocene. For ex- ample, the general northerly orientation of ridges in the Mount Nast-Bald Eagle study area (figs. 2, 6) appears related to regional joint and fault systems. These val- leys were occupied by northward-flowing valley glaciers. Owing to predominantly westerly winds and to less direct exposure to afternoon sun, the accumulation of snow and ice was heaviest on the east or lee sides. There- fore, cirques on the higher slopes developed much more commonly on the east- and northeast-facing sides. The present ridges are asymmetric-steeper on the east and more rounded on the west. Gravitational spreading features are more commonly observed high on the west sides of these ridges than on the more deeply sculptured east sides. This may be due in part to greater remaining mass with resulting higher gravitational stresses on the west sides or, possibly, in part to removal of the fea- tures of gravitational spreading by erosion on the east sides. MICROCRACKS AND JOINTS In relatively homogeneous geologic terranes, sackungen appear to be related to joint systems that are the macroscopic equivalents of microscopic frac- tures in the rock. A thin section of an oriented sample taken from the cirque southeast of Bald Eagle Mountain shows that the rock is cut by numerous microscopic open fractures, some of which cut across grain boundaries, some of which do not (fig. 32). The thin section was cut normal to the major joint set, which dips 73-85° SE., and strikes N. 47-67° E. At the point at which the oriented sample was taken for the thin section, the major joints strike N. 47° E. and dip 85° SE. (fig. 7). This orienta- tion can be compared with the average N. 50° E. trend of the graben and hillside trenches on Bald Eagle Moun- tain. The thin section also intersects the foliation, which here strikes approximately N. 45° W. and dips 30° NE. Microscopic fractures in the thin section, parallel to the major joint system, cut across the foliation. Some of the fractures are partly filled with quartz, others are open. A thin section, from an oriented sample taken from the face of the uphill-facing scarp on Mount Massive, was cut parallel to the secondary joint set, and across both the irregular foliation and the major joint set, which strikes N. 20° E. and dips 62° SE. The section was normal to the plane of the major joints. Foliation was indistinct in the section. Prominent microscopic fractures in the thin section were seen to be parallel to the major joints. Some fractures were seen to be wholly within individual grains; whereas, others were con- tinuous across several grains. RELATION OF SACKUNGEN TO TOPOGRAPHY AND ROCK STRUCTURE 19 Hi FIGURE 28.-Southwest-facing slope of Contact Mountain, Stillwater Complex, Montana. Layering in the basic igneous rocks dips to the left (northeast) at angles of 50-60° into the slope. Some of the larger trenches are indicated by arrows. Total height of the slope is about 3,850 ft. FIGURE 29.-Aerial oblique view of one of the principal uphill-facing scarps on the southwest slope of Contact Mountain, Montana, strik- ing about parallel with the slope contour and dipping into the slope at the same inclination as layers within the intrusive body. The ridge on the downhill side of the trench in the lower center of the photograph is capped in places by remnants of glacial till. FIGURE 30.-Joints in the layered intrusive rocks of the Stillwater Complex on Contact Mountain, Montana. The principal joints, which also control the direction of many sackung trenches and scarps, are parallel to the layering. Other well-developed joints, nearly vertical and nearly normal to the strike of the layering, appear in the background. 20 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. FIGURE 31.-Large graben on the crest of Contact Mountain. The long, high slope to Boulder Creek, shown in figure 28, is out of view to the left. Joint systems control the zig-zag direction of the principal failure surface on the right (northeast) side of the graben. Another oriented sample was taken from the cirque between the two arms of Surprise Ridge; a thin section of the sample was cut normal to the vertical joints at the site, which trended N. 20° E. Microscopic fractures with the same orientation as the vertical joints (the ma- jor set) were clearly visible in the thin section. The strike of the major joint system on Bald Eagle Mountain and in the cirque to the southwest is similar to the strike of the graben and trenches of the sackung mass. The displaced mass, to the southwest of Bald Eagle Mountain, consists of blocks of rock ranging from a few inches to several feet across. The rock mass that has bulged out into the canyon wall of Busk Creek con- sists of blocks that have moved individually, as in- dicated in figure 33, as well as in aggregates that form larger coherent units. Each larger unit has separated from its neighbor along the major joint planes that trend northeast about parallel to the contours on the slope, and that control the direction of the hillside trenches. Individual, smaller blocks apparently also separated along this joint set as well as along the other FIGURE 32.-Photomicrograph of thin section cut from oriented sam- ple from the cirque southeast of Bald Eagle Mountain. The section is normal to the principal joint set, which is paralleled by the numerous microscopic fractures. RELATION OF SACKUNGEN TO TOPOGRAPHY AND ROCK STRUCTURE 21 FIGURE 33.-Joint-bounded blocks in the lower part of the cliff below station 3 (fig. 6). This is in a zone of some rotation of individual blocks and probable dilation, although the mass itself has not yet fallen. The observation of principal joint direction, shown by dashed lines in figure 10, is different from the usual trend of principal joints away from the disturbed zone. two sets, one of which is vertical and trends sub-normal to the major set (N. 24° W.), and one of which trends N. 45° W. and dips 30° NE., so that a component of the dip is outward toward the valley. Movement of in- dividual blocks also can be seen in a quarry along the road below and northeast of the bulge of the sackung (fig. 34). The direction of principal joints in the Bald Eagle Mountain-Mount Nast area has controlled the orien- tation of ridges and valleys developed during erosion by ice and water. Trenches and upward-facing scarps developed by gravitational spreading of ridges are usually more or less parallel to ridge axes and slope con- tours, and they also tend to make use of any zones of weakness, such as the principal joints. Thus, there is commonly a concurrent direction of ridge axes, con- tours, trenches and scarps, and principal joints. More- over, other joint sets locally are well developed, so that rocks of the ridges are divided into blocks having dimensions of one or a few feet. At the scale of the mountain masses, the individual rigid units are much like grains in a small pile of sand a few feet high. In the mountain, the units are better interlocked, and, of course, they are subject to much higher gravitational forces; but the intimate division permits use of mathematical tools for analysis that are appropriate for particulate bodies, as is done in a later section. FAULTS AND FAULT ZONES Fault zones are usually intensely fractured and are weak; they are places where sackungen may be expected to occur. We have observed uphill-facing hillside scarps formed by gravitational movement along faults and fault zones in a few places. The principal scarps and graben at Ute Peak in the Williams Fork Mountains follows the course of a fault previously mapped by FIGURE 34.-Joint-bounded blocks in the quarry above the road in Busk Creek valley northeast of and below the principal area of trenches. Each large block has moved outward 1-4 in. relative to the block beneath on joints that dip at a low angle obliquely toward Busk Creek. This illustrates bulging movements on the lower slopes of the valley that are elsewhere obscured by colluvium and talus. 22 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. Tweto and Reed (1973b). Certainly, there is geomorphic evidence for either tectonic faulting or gravitational movement since the form of the mountain was estab- lished, but it is not known whether there is independent evidence for a tectonic fault. The scarp and trench on the northwest ridge of Mount Massive, which is definitely a gravitational-failure structure, was also previously mapped as a fault (Tweto and Reed, 19732). Farther northwest of Mount Massive, on the ridge west of Pear Lake, Notch Lake, and Windsor Lake, there are also conspicuous uphill-facing scarps and grabens along a previously mapped fault (fig. 6). However, this struc- ture may well be a fault that extends to some depth, because, beneath its northwest extension, an intensely fractured zone was encountered when driving the Charles H. Boustead tunnel, about 1,400 ft beneath the surface (fig. 6). Remedial work in the fracture zone delayed tunneling progress for nearly 11 months. The east side of the valley of Busk Creek is marked by a prominent linear bench. Above the bench is a scarp or steep slope, approximately parallel to the contours through much of its course, that extends from well southwest of the sackung-affected area, northeastward nearly to the mouth of the valley of Busk Creek (figs. 4, 6, and 35). The trace of the bench on the surface is interrupted by rock-fall deposits below the sackung area, and the scarp in this area is unusually steep and high. This scarp may follow a zone of highly fractured rock, which may have had significant influence on the erosional development of Busk Creek valley by both water and ice, and thus on the topographic setting for the sackungen. The influence on the location of the sackung may have been more direct. The unusually high scarp below station 3 at the lower edge of the zone of trenches is on line with the projection of the bench and scarp on the slopes to the southwest and northeast, and provides a steep, free face toward which gravitational movements could occur. Farther up Busk Creek valley, southwest of the well- developed sackungen, is an area with an unusual pattern of intersecting, shallow trenches that is about 0.6 mi north-northeast of Rainbow Lakes and on the slope above the southwest continuation of the bench and scarp along the southeast side of Busk Creek valley (figs. 36, 37). A few small, uphill-facing scarps do exist; this part of the slope may exhibit the initial stages of sackung development, before the well-jointed mass has formed into defined groups of failure units. DIOBSUD RIDGE, WASHINGTON A report on the Straight Creek fault zone in the Diob- sud Ridge area of northern Washington State (McCleary and others, 1978), described uphill-facing scarps along a fault-line valley that marks the trend of the Straight Creek fault (fig. 38). A trench 5 ft in depth that was dug normal to one scarp and the depression immediately uphill from it revealed a zone of crushed and sheared rock in the depression that was interpreted to have formed by tectonic movement, although the trench showed very little that would conclusively identify the scarp as being of tectonic rather than gravitational origin. However, the presence of similar scarps on both sides of the fault-line valley strongly sug- gests that the scarps are gravitational, as the move- ment that formed them was downhill-side-up on both sides of the valley. This means that if the movement were tectonic, it would have been in opposite directions on opposite sides of the valley, which seems unlikely. The pattern of movement is, however, entirely consis- tent with gravitational movement along pre-existing weaknesses in the rock-in this locality, along a fault zone. The study by McCleary and others (1978) included ex- amination of aerial photographs covering 2,100 mi? of the North Cascades. Fifty sackunglike features were identified, of which 28 were confidently judged to be gravitational-spreading features. Of these, 19 were within a restricted zone 10 mi wide centered approx- imately on the Straight Creek fault zone, and the report concluded that the sackung features may have been triggered by active seismicity associated with the zone. ELASTIC-PLASTIC STRESS ANALYSIS OF GRAVITATING RIDGES Analytic studies of stresses in ridges and slopes by W. Z. Savage and his coworkers (Savage and others, 1985; Savage and Swolfs, 1986; Savage and Smith, 1986) have been applied to the problem of gravitational spreading of ridges with emphasis on the origin of uphill-facing scarps and ridge-crest grabens (Savage and Varnes, 1987). The analyses include an exact elastic solution for gravity-induced stresses in an isolated ridge of generalized parabolic cross section and a plastic solu- tion for gravity-induced deformation of a slope yielding under the Coulomb criterion. These are appropriately combined to delimit regions of potential failure by plastic flow under given conditions of geometry and material properties. The elastic solution by Savage and others (1985) for gravitational stresses in symmetric ridges is based on the Kolosov-Muskhelishvili (Muskhelishvili, 1953) method of complex potentials for plane elasticity. A con- formal mapping function is used to transform an isolated symmetric ridge into a half-plane in which ex- pressions are derived for gravity-induced stresses in the ELASTIC-PLASTIC STRESS ANALYSIS OF GRAVITATING RIDGES FIGURE 35.-View to the southeast over Busk Creek valley showing, on the right, the cliffs and rock-fall deposits below the area of sackung trenches. On the left, the prominent bench and low scarp continue to the northeast about halfway up the slope from the road. FIGURE 36.-Aerial oblique view of an area southeast of Busk Creek and southwest of the tributary valley that forms the southwestern border of the well-developed sackung trenches. This slope is in a similar topographic setting, just above the bench and scarp along the southeast side of Busk Creek valley. It may be in the initial stages of sackung development. 28 24 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. FIGURE 37.-Stereopair of vertical aerial photographs showing area of intricate pattern of shallow trenches (at arrow) above the prominent bench and scarp on the southeast side of Busk Creek valley. This area is in a topographic setting similar to that of the well-developed sackung across the tributary valley to the north, and may be in an earlier stage of development. ridge (fig. 39). The mapping used to transform a sym- metric ridge in x,y coordinates into a half-plane in u,v coordinates and the definition of the parameters a and b, which describe the shape of the ridge, are illustrated in figure 39. Specifically, a and b are parameters used in the conformal mapping where b is the ridge height and a + b/2 represents the x coordinate of the inflec- tion point on the ridge flank. Savage and others (1985) derived expressions for horizontal, o,, and vertical, oy, total normal stresses and shear stress, o,,, in and away from the ridge of the form 0,= pgbFy(u, v, a, b, »)+ T—W (1) -V oy= pgbFy(u, v, a, b, (2) pgbFg(u, v, a, b, ») (3) where p is the density, g is the gravitational accelera- tion, » is Poisson's ratio, and Fj, Fy, and Fg are com- plex functions of u, v, a, b, and ». Effective stresses “x and oyare defined as 0 “0x -P and 0,=0,-P, where P is pore pressure. Stresses given by equations 1, 2, and 3 satisfy the conditions that shear and normal stresses are zero on the ridge surface and satisfy the condition of plane strain parallel to the ridge. The stress state away from the ridge is given by assuming vanishing far- field horizontal displacements, which requires that the stresses far from the ridge are 0,= 1 27 0,=pgY, and 0,y=0. Figure 40 shows contours of normalized effective stresses ogpgb a/pgb, and 0x !ogb by the exact solu- tion for alb = 1, P = 0.0, and v = 0.25. Note that by decreasing a for a given b, narrower and steeper ridges can be created. The predicted magnitudes of gravity-induced stresses from point to point in idealized ridges of the type shown in figure 39 are then compared to stress levels necessary ELASTIC-PLASTIC STRESS ANALYSIS OF GRAVITATING RIDGES 25 Y. UMBLA - -a- CL -_ 0 50 100 MiLES OREGON FIGURE 38.-Index map of the State of Washington showing location of the Skagit River, Diobsud Ridge, and, by dotted line, a part of the trend of the Straight Creek fault zone. for yielding. The yield condition is that of Coulomb in the form given by Drucker and Prager (1952); [lo,-oy)? + 40,y"] = sin ¢ (0, + oy + 26 cot ¢), (4a) or as sing (o,+oy+2¢ cot) = (4b) a + 404y ] where ¢ is the angle of internal friction and C is the cohe- sion (resistance to shear) across a plane having zero | FicurE 39.-Conformal transformation for a symmetric ridge in x,y normal stress. coordinates to a half-plane in u,v coordinates and the definition of $ & cas the parameters a and b which describe the shape of the ridge. Here, In equation 4b, F represents the ratio of resisting b represents the ridge height. When u=a and v=0, then x=a+(b/2) shearing stresses (term in numerator) to maximum and y=b/2, which are the coordinates of the inflection point on the shearing stresses (term in denominator) at a point in the | _ ridge flank. 1 I I 1 I T 1 K |_ 2- |_ - |_ - 0 0.403\ 0 0-6\ 0 006 | --- ag. c --- 2, ~ 1.2 C Q} _1 fe ___ __ zz --8.6-____ -1 -__ -1}- 20 - Rel 2 7-8\ _ > > § 2, -__, * m2 fl, ____zz of gai -2 |- A- -» |- _ .\ 3.0-________] 2 & hes —_/.—1.2/— -3 ho- - -3 |- -] * \- [T-----4 2x Ba | | | r | | m | o 1 2 3 4 o 1 2 3 4 o 1 2 3 4 x/b x/b x/b F1GURE 40.-Contour plots of agpgb. aypgb, and a;/pgb from left to right, respectively, for a symmetric ridge where a/b = 1.0 and Poisson's ratio, » = 1/4. Compressive stresses are taken to be positive and pore pressure is zero. 26 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. gravitating elastic body shown in figure 39. When F=1, the maximum shearing stresses on suitably oriented planes at this point is equal to the resisting shearing stress, and failure is imminent. When F>1, the resisting shear stress exceeds the maximum shear stress, and the material at the considered point is stable. Some predicted failure zones, calculated by equations 1 through 4, for zero pore pressure and a few values of the parameters a, b, », $, and c, are shown in figure 41. For simplicity, zero pore pressures are assumed, and because of symmetry, only the right half of the ridge is shown. The depth to which the zone of potential instability of the slope extends is seen to depend not only on the steepness of the slope but also on the value assumed for cohesion (under conditions of zero pore-water pressure and angle of internal friction, =30°) (fig. 41). The depth of the failure zone increases with steepness of the slope, markedly decreases with increasing cohe- sion, and can be shown (Savage and Smith, 1986) to in- crease with increasing pore-water pressure. Plastic flow occurs in the failed region in response to gravity loading. Stresses in the failed region must satisfy the yield condition (equation 4), and the condi- tions of static force equilibrium. Also, velocities in the failed region must satisfy the continuity condition. Ex- pressions for stresses and velocities that satisfy these conditions for a two-dimensional uniformly sloping half- space of Coulomb plastic material under elevated pore pressure and under gravity loading are given by Savage and Smith (1986). Savage and Smith also give expressions for a system of coincident stress and velocity characteristics along which discontinuities in velocity are propagated through the plastically flowing mass. These character- istics are physically manifested as rupture surfaces. The expressions for stress, velocity, and associated rupture surfaces given by Savage and Smith (1986) are exact only for uniformly sloping failed regions of cons- tant thickness. However, these expressions apply ap- proximately for failed regions of the type shown in figure 41, if the variation in depth of failure along the ridge flank is small and if the radius of curvature of the surface slope is large, compared with the failed thickness. Clearly, the approximations are poorest for steep slopes and best for gentle slopes. A sketch of the predicted slip-line field in potential flow regions is shown in figure 42, which shows results of an analysis of a complete ridge with convex-upward slope at the upper part, a straight part or an inflection, and concave-upward lower valley wall. These three regions have different responses. The upper subregion is in extending flow, and the two complementary sets of potential rupture surfaces have opposite sense of | m= Com Ge \\\~«sw.:.:.~.~.. m ore oto x/b FIGURE 41.-Diagrams showing predicted zones of potential failure in a symmetric ridge for zero pore-water pressure and angle of internal friction $=30°. A, Shows the effect of cohe- sion, C, on depth of potential failure: cohesion is 0.01 in the diagonal-ruled case, 0.06 in the cross-hatched case. Cohesion is in units normalized with respect to gb (density X gravita- tional constant 'X slope height). B, Shows effect of Poisson's ratio: »=0.35 in diagonal-ruled area, »=0.45 in cross-hatched area. Cohesion is 0.01 in both cases. C, Shows effect of steeper slope; c=0.01, »=0.35. The x and y coordinates are normal- ized with respect to slope height, b (Savage and Varnes, 1987). shear. Uphill-facing surface scarps will develop along the steeply dipping set. More gently dipping downhill- facing scarps of the other set are possible but are com- monly absent if the steep set is developed. Very often, the region of extension is preferentially developed or, at least, is more commonly preserved and easily ob- served than the lower region of compression in the lower valley wall. A subregion of plug flow may be present if the slope is long and planar. The subregion of com- pression in the concave part of the slope may have been removed by erosion in precipitous valley walls or may be obscured by colluvium, landslide debris, or talus. One should regard the basal surface forming an envelope to potential shear surfaces as a mathematical construction-the boundary between an elastic region below and a potentially failing region above. The plastic-flow solution requires that in the sub- region in extension an initial discontinuity on the steep set will propagate upward from the plastic-elastic ACKNOWLEDGMENTS 27 Graben Sackung trenches 17 f ~~ Plug flow Extending flow Compressive a y0|- 23 | | | | 0 1 2 3 4 5 x/b FIGURE 42.-Sketch of the potential flow regions and predicted senses of shear on examples of rupture surfaces for a symmetric gravitating ridge. Inactive rupture surfaces are dashed. The x and y coordinates are normalized with respect to slope height, b (Savage and Varnes, 1987). boundary with exponentially increasing relative displacement toward the ground surface; the converse is true of the downhill-facing discontinuities. In the compressive-flow region, the opposite holds. In summary, the principal contributions of the analysis toward an understanding of sackungen mechanics in homogeneous terranes are as follows: 1. The steeper the slope, the deeper the zone of poten- tial instability. 2. Any significant cohesion drastically decreases the thickness of the failure zone. 3. Development of the set of uphill-facing scarps, com- plementary to the more usual downhill-facing scarps of conventional landslide, is not only possi- ble but may be favored under the proper conditions of topography and rock structure. Preference for the uphill-facing scarp set suggests that the moun- tain has "solved" a least-work problem and has chosen to activate slip surfaces of the shorter set that extend to the free surface rather than longer surfaces that penetrate to increasing depth. 4. Increase in pore-water pressure increases the depth of the unstable zone. CONCLUSIONS Field observations in the Sawatch Range and the Williams Fork Mountains of Colorado, where the rocks are relatively homogeneous migmatites and granitic rocks or gneiss, show that the rocks involved in sackungen commonly move valleyward normal to ma- jor joint sets that strike approximately parallel to valley walls. Dips of the joints are variable and joints may dip steeply either into or out of the slope. The rocks are generally broken by minor joint sets and(or) planes of foliation that are more or less normal to the valley sides, as well as by joints or planes that are nearly flat or dip slightly valleyward, so that at least three sets of discon- tinuities commonly are involved. Joint sets and other planes generally cannot be measured reliably within the sackungen, because the blocks composing the moving masses have rotated so that the original orientation of joints and foliation can- not be determined. Exposures are generally good and measurements reliable, however, in nearby glaciated areas above timberline in these high mountain regions, particularly in glacial cirques. Thin sections of samples of fresh rock taken where jointing and foliation can be measured show that microscopic fractures seen in thin section have an orientation similar to that of the open principal joints visible in the field and similar to that of the trenches characteristic of the sackungen in two areas. Where gravitational sackung-type movement has taken place along tectonic shear zones, it may be dif- ficult to ascertain whether the scarps are the result of tectonic activity or the result of gravitational move- ment that has used a previously existing zone of weakness, or both. Uphill-facing scarps in any seismical- ly active area should be examined carefully, to attempt a determination of whether they are of gravitational or tectonic origin. A possible criterion for making this distinction is that scarps of gravitational origin are more likely to have their location, orientation, continui- ty, and sense of displacement determined by local topography than are fault scarps resulting from regional tectonic stresses. Grabens and hillside trenches that have formed where bedding planes or other discontinuities dip into a slope may have formed by toppling, bending of beds, or spreading of a ridge. All these mechanisms have been suggested by various authors. An elastic-plastic analysis indicates that ridge-crest grabens and uphill- facing scarps may result from activation of the set of potential shear surfaces that are complementary to the usual surfaces of slump-type landslides. ACKNOWLEDGMENTS We owe much to Czechoslovakian geologists, who, for many years, have made excellent studies of gravita- tional spreading of ridges in their country. We are in- debted, particularly, to Arnold Neméok and Tibor Mahr, whose untimely deaths dealt a serious blow to sackung research, and to their colleagues Josef Malgot, Jaroslav Pasek, and Milan Matula. In our fieldwork in the Western United States, we have been helped at 28 TOPOGRAPHIC AND STRUCTURAL CONDITIONS, GRAVITATIONAL SPREADING, WESTERN U.S. various times and for various periods by our coworkers Sigrid Asher-Bolinder, Robert Fleming, Kenneth Segerstrom, William K. Smith, and Katharine Varnes, and by field assistants Greg Twombly and Erik Shaw. Lastly, the special skills of helicopter pilots Burt Metcalf, Paul Kinsey, Marc Pasewalk, and Jim Innes enabled us to go wherever required and brought us back, often under difficult conditions. REFERENCES Drucker, D.C., and Prager, W., 1952, Soil mechanics and plastic analysis or limit design: Quarterly of Applied Mathematics, v. 10, no. 2, p. 157-165. Ludington, Steve, and Yeoman, R.A., 1980, Geologic map of the Hunter-Fryingpan Wilderness Area and the Porphyry Mountain Wilderness Study Area, Pitkin County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-1236-A, scale 1:50,000. McCleary, Jeff, Dohrenwend, John, Cluff, Lloyd, and Hanson, Kathryn, 1978, 1872 earthquake studies, Washington Public Power Supply System, Nuclear Project Nos. 1 and 4, Straight Creek Fault Zone Study: Woodward-Clyde Consultants, San Fran- cisco, Calif., prepared for United Engineers and Constructors, Inc., Contract No. H.O. 52028, 72 p. Muskhelishvili, N.1., 1953, Some basic problems of the mathematical theory of elasticity: Groningen, The Netherlands, Noordhoof, 718 p. Radbruch-Hall, D.H., 1978, Gravitational creep of rock masses on slopes, in Voight, Barry, ed., Rockslides and avalanches, Vol. 1, Natural Phenomena: Developments in Geotechnical Engineer- ing 14A, Amsterdam, Elsevier Scientific Publishing Co., p. 607-657. Radbruch-Hall, D.H., Varnes, D.J., and Savage, W.Z., 1976, Gravitational spreading of steep-sided ridges ("sackung") in western United States: International Association of Engineering Geology Bulletin 14, p. 23-35. Savage, W.Z., and Smith, W.K., 1986, A model for the plastic flow of landslides: U.S. Geological Survey Professional Paper 1385, 32 p. Savage, W.Z., and Swolfs, H.S., 1986, Tectonic and gravitational stress in long symmetric ridges and valleys: Journal of Geophysical Research, v. 91, no. B3, p. 3677-3685. Savage, W.Z., Swolfs, H.S., and Powers, PS., 1985, Gravitational stresses in long symmetric ridges and valleys: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, v. 22, no. 5, p. 291-302. Savage, W.Z., and Varnes, DJ., 1987, Mechanics of gravitational spreading of steep-sided ridges ("sackung"): International Associa- tion of Engineering Geology Bulletin, no. 35, p. 31-36. Segerstrom, Kenneth, and Carlson, R.R., 1982, Geologic map of the band- ed upper zone of the Stillwater Complex and adjacent rocks, Stillwater, Sweet Grass, and Park Counties, Montana U.S. Geological Survey Miscellaneous Investigations Series Map I-1383, scale 1:24,000. Tweto, Ogden, 1973, Reconnaissance geologic map of the Dillon 15-minute quadrangle, Summit, Eagle, and Grand Counties, Col- orado: U.S. Geological Survey Open-File Report 1776, scale 1:62,500. Tweto, Ogden, 1974, Geologic map and sections of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado: U.S. Geological Survey Miscellaneous Geological Investigations Map 1-830, scale 1:24,000. Tweto, Ogden, and Reed, J.C., Jr., 1973a, Reconnaissance geologic map of the Mount Elbert 15-minute quadrangle, Lake, Chaffee, and Pitkin Counties, Colorado: U.S. Geological Survey Open-File Report 1777, scale 1:62,500. Tweto, Ogden, and Reed, J.C., Jr., 1973b, Reconnaissance geologic map of the Ute Peak 15-minute quadrangle, Grand and Summit Coun- ties, Colorado: U.S. Geological Survey Open-File Report 1779, scale 1:62,500. Zischinsky, Ulf, 1969, Uber sackungen: Rock Mechanics, v. 1, no. 1, p. 30-52. # U.S. GOVERNMENT PRINTING OFFICE: 1989-773-047/06,006 REGION NO. 8 AUG U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1494 PLATE 1 122° ey f 2. a em- ; 7 ae] 38° - ¥ C+ C> 34" [+ EXPLANATION 330 u ?A _ STREAMFLOW-MEASURING SITE - Number corresponds to site number in table 23 and station data { | | | | \ | | 0 0 0 Base from U.S. Geological Survey 121° 120° 119° 118 117 116 State Base Map, 1:1,000,000, California, 1970 SCALE 1:1,000,000 0 25 50 75 100 _ MILES I I I | I I T I I I 0 25 50 25 100 KILOMETERS MAP SHOWING SITES IN SOUTHERN CALIFORNIA WHERE STREAMFLOW DATA WERE OBTAINED FOR FLOODS OF FEBRUARY 1980 U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1494 35° |- 110° 109° """" pge ] 1; Bacobi m. ‘: ‘ AZ y g | I (eas O ,,L)_.. 350 >< Lu 3 34° a i - 34° 3 LU z i -i 33° E XPLA N A TIO N 45A STREAMFLOW-MEASURING SITE- Number corresponds to site number in table 24 and station data a #. Base from U.S. Geological Survey 114° 112 111° 109° State Base Map, 1:1,000,000, Arizona, 1974 SCALE 1: 1,000,000 0 25 50 75 100 MILES | | | | ] I T T | T 0 25 50 75 100 KILOMETERS MAP SHOWING SITES IN ARIZONA WHERE STREAMFLOW DATA WERE OBTAINED FOR FLOODS OF FEBRUARY 1980 33°45" to 33°15. U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY R. 5 W. 112°45" 111945 S Daisy Agua Fria River below Waddell Dam 0900 hours, Feb. 14 1600 hours, Feb. 14 0800 hours, Feb. 15 1800 hours, Feb. 19 0130 hours, Feb. 20 >. N's v3 f er N 4 I w & =: | ln \ | a % k "2505 ’ LX ture Gold Mme Me KL : “My; a - ( y J ; fosom Y-, \ Lake Pleasant Park Road washed out. Bridge on State Route 74 received severe structural damage. F MOUNT N SUG skid OUNTAI os 4 i A’j \ Tojvm NAT: ionkL Forest F“ Verde River below Bartlett Dam 2 0800 hours, Feb. 15 3 1800 hours, Feb. 15 >‘A‘?€(ffi”§’ ett “fiesta“: oir [mt/emu MOUNTM fz: j cumfieunmm * Erosion around piers at Grand Avenue bridge. Peak stage and discharge only at gaging station. ,/" \\ Spil twaNdSA x % y | Tat: i / f ~A an is | ¢ ~} C "I:" My”? ~ MC DO Wgfli PEAK ixie Mine Bear. BARTLETT-DAM WEST CORANJTE MTN \ CRANE MTC x HERDER MOUNYAJN £7 SUGéRiOAF MQunNTA G! i g] ”39 TL w SOOKOUT t ~~ ~_-- SHA , shoulders damaged JL 2149 Verde River near Scottsdale Gage and approaches to bridge washed out j= 5 A- -B Interstate 10 bridge under construction; new channel Salt River at Jointhead Dam J 1 0700 hours, Feb. 14 3 0100 hours, Feb. 16 prcien bypassed bridge; see fig. 53 17 # M 2 1400 hours, Feb. 15 L ['] Hohokam Freeway nearly complete; ste‘WAkr MQUNWN 298 msTFWART mou Stew approaches washed out, delaying Indian School Road; AVENUE bridge destroyed State Route 85 ( U S 80 ) ;approaches | UNTERSTATE inundated and badly damaged; were repaired as soon as water receded C 2 eal Spbstation "n | Clue Q5 ® (QC?! f B i V -L! Sky Harbor Airport Fe runways damaged + > Agua Frla River at Avondale fermjville 3 2100 hours, Feb. 14 NGEAN RESERVA‘HO r/«A/ WE” f RANITE REEF DAM Salt River below Stewart Mountain Dam 2 1000 hours, Feb. 15 \ 3 2100 hours, Feb. 15 Approaches to Blue Point Bridge -_ SCOTTSDALEROA \ washed out 'wwwk#~g 2400 hours, Feb. 14 1300 hours, Feb. 15 0500 hours, Feb. 20 itflpccye Junctan f/E © 3» 0700 hours, Feb. 20 | Salt River at Granite Reef Dam 1 2000 hours, Feb. 13 2 1000 hours, Feb. 15 3 2200 hours, Feb. 15 Gila" 7 "> .[ Gila River at U.S. 80 2400 hours, Feb. 14 2 - Unknown; masked by Agua Fria River K riff? D__ - * Branch m + £ anal {* Mill Avenue; grade-level crossing J K for three northbound lanes washed | [_| __% out; four lanes squeezed onto ’ bridge that normally carries three southbound lanes. NTY j _ Xx U A OPA © } & . Fina, cou Tve MARI COne C\ 187 / sy ad YK Me / A 35 1500 hours, Feb. 15 ( estimate ) .N o Mine Well- 1p. ty § (f R ”LL; Sprif # s 750 Gillespie Dam Salt River at 35th Avenue 1600 hours, Feb. 14 1800 hours, Feb. 15 3 0800 hours, Feb. 16 ( estimate ) Recorder removed before crest Grade-level approaches to small bridge under water during entire flood period. Recorder submerged before crest of flood. |__ ys omens ramos we? ~~ S? - § 4- - f” - ”gm. umes G/ELESPIE DAI Pier footings of Interstate 10 undermined; highway closed ”LAW- for 2 weeks NG mower/w a {ral -& .- apm Ramb id Vafirgy * Four-lane bridge on Central | Gila River below Glllespne Dam 0800 hours, Feb. 15 M 4,» __ k- - -L- thtenhggae A? | I Water a Labor gamp - Sia ___if L_ } \\/ 1830 hours, Feb. 16 1800 hours, Feb. 20 N ONTEZUMA PEAK \\ 4337 meme rest mm < Avenue remamed open anis Annam y, Tre em gn € 1 Jim h__| “N‘GdRsz "MAR! 009A COUNTY | I } T | e\} Base from U.S. Geological Survey Mesa, 1:250,000, 1954-69, and Phoenix, 1:250,000, 1954-69 SCALE 1:250,000 o--» 15 20 MILES | | I 20 KILOMETERS MAP SHOWING DAMAGE INFORMATION AND TIME AND DATE WHEN FLOODWATERS REACHED SELECTED ROAD CROSSINGS IN AND NEAR PHOENIX, ARIZONA, FEBRUARY 13-20, 1980 111945 - 33°45" 33°30° 33°15. A Salt River at Granite Reef Dam 1 2000 hours, Feb. 13 2 1000 hours, Feb. 15 3 2200 hours, Feb. 15 Agua Fria River below Waddell Dam 4 0900 hours, Feb. 14 5 1600 hours, Feb. 14 6 0800 hours, Feb. 15 7 1800 hours, Feb. 19 8 0130 hours, Feb. 20 Ge 7G “(a 344 4 Pt. me s (3) PROFESSIONAL PAPER 1494 PEATE 3 EXPLANATION Bridge and road crossings-All improved crossings of the Salt, Verde, Agua Fria, and Gila Rivers are shown; those without bridge symbol are at grade level Streamflow-gaging station or data-collection site Salt, Verde, and Gila Rivers: Name of gaging station 1 gives the time and date when water first reached the station ( at Granite Reef Dam it is the time when water began to flow over the dam ) 2 gives the time and date of the most rapid rise 3 gives the time and date of the flood crest Agua and Gila Rivers: Name of gaging station 4 gives the time when water was first released to the river or reached the Avondale station 5 gives the time the constant release of February 14 began or reached the Avondale station 6 gives the time of the February 14 crest 7 gives the time when the February 19 rise began 8 gives the time of the February 20 crest Bridge was one of four that remained open during flood NOTE; All bridges from Hayden Road to 51st Avenue ( inclusive ), except Mill and Central Avenues, were closed because of washed -out approaches or structural damage. Bridges at 48th Street, 16th Street, and 19th Avenue had been destroyed by floods in 1978 and had been replaced with grade-level detours prior to the 1980 flood. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY 45°15 1230". J 18 18 5 730" 12°32" 30" I CORRELATION OF MAP UNITS @a | op QUATERNARY OTsi QUATERNARY AND on (OR) TERTIARY Tb TERTIARY Unconformity (OR) LATE ARCHEAN LATE ARCHEAN LATE OR MIDDLE ARCHEAN MIDDLE (?) AND EARLY (?) ARCHEAN DESCRIPTION OF MAP UNITS Sand and gravel (Quaternary)-Unconsoli- dated to poorly consolidated Oa Alluvial stream deposits Ob Basin fill-Mostly in upper reaches of Sweet- water Creek QTsi Siliceous fault line deposits (Quaternary and (or) Tertiary)-Jasperoid along Carter Creek fault, silicified breccia along Stone Creek fault OTs Pediment gravel and debris (Quaternary) and siltstone, sandstone, and conglomerate (Tertiary) Tb Basalt (Tertiary)-Remnants of valley flows, in part equivalent to basalt a few miles east of map area yielding K-Ar age of about 4 m.y. (Pliocene) - Diabase (Middle Proterozoic)-Narrow dikes, most along fractures related to northwest- trending faults Undeformed but slightly altered. Rb-Sr age about 1,425 m.y. Pegmatite (Early Proterozoic(?) and (or) Late Archean) Small bodies-Undeformed, tourmaline-bear- ing; many rudely zoned, having quartz core. Not separately distinguished in all parts of map area. Probably Early Proterozoic in age Sheets and dikes-Abundant; composed mostly of coarse-grained alkali feldspar and quartz, commonly fractured but rarely foliated. Mostly Late Archean in age Granite gneiss (Late Archean)-Massive to foliated, locally mylonitic. In part igneous intrusive, in part product of granitization of pre-existing pelitic strata. Not physically distinguishable from some phases of older quartzofeldspathic gneiss. Age about 2,750 m.y. Amphibolite (Late or Middle Archean)-Foliated sheet-like bodies composed mostly of horn- blende and plagioclase; some garnetiferous. Mostly mafic sills initially, of two or more ages. Some small bodies may be metavolcanic or derived from metasedimentary diopside gneiss by retrograde metamorphism MIDDLE PROTEROZOIC EARLY PROTEROZOIC AND 30' - Ultramafic rocks (Late or Middle Archean)- Small plutons in south-central part of map area, pods and lenses elsewhere. Bodies too small to be shown at map scale indicated by cross Christensen Ranch Metasedimentary Suite (Late or Middle Archean)-Divided on basis of lithologic units (not a stratigraphic sequence) Quartzite- Thin beds of orthoquartzite, mostly white to yellow, locally greenish | #-WVci Iron-formation-Alternating thin layers of mostly magnetite and quartz, commonly contorted. Beds that are too thin to be shown at map scale are indicated by solid red line WVem Marble-Medium- to coarse-grained, generally dolomitic and containing variable amounts of diopside, tremolite, serpentine, phlogopite. Host rock for widely distributed deposits of tale WVcu Undifferentiated metasedimentary rocks- Includes quartz-mica schist, sillimanite schist; tremolite, phlogopite, and anthophyllite schist; diopside and epidote gneiss; small bodies of amphibolite and granitic gneiss Quartzofeldspathic gneiss (Late or Middle Archean)-Mostly massive to well-foliated reddish-brown granitic gneiss, in part garneti- ferous, locally containing thin lenses and layers of amphibolite. Encloses tectonic slices and infolds of Christensen Ranch metasedimentary strata, mostly marble. Poly- genetic in origin, in part igneous, in part metasedimentary Older gneiss and schist (Middle(?) and Early (?) Archean)-Layered biotite-homblende-garnet gneiss, augen gneiss, migmatite. Corundum- bearing schist and anthophyllite schist in sec. 20, T.8 S., R. 6 W. Age uncertain but assumed to be older than quartzofeldspathic gneiss unit (Wag) - Contact-Dashed where approximately located or inferred. Some contacts mark surfaces of tectonic dislocation Fault-Dashed where approximately located or inferred; dotted where concealed Strike and dip of layering in metasedimentary 20 rocks -- Inclined =- Vertical op Strike and dip of foliation A- Inclined yo Vertical ->50 Bearing and plunge of lineation (rodding, minor fold axis, mineral elongation)-May be combined with strike and dip symbol 2730" I T8 S 1.9 5 12°32 30" Base from U.S. Geological Survey Ashbough Canyon, Christ ensen Ranch, Dillon East, Elk Gulch, Mine Gulch, 1961 TRUE NORTH APPROXIMATE MEAN DECLINATION, 1989 GEOLOGIC MAP OF THE SOUTHWESTERN RUBY RANGE, MONTANA 25° R 7 W R 6 W L] 1 5 0 1 KILOMETER C eT ~d - Hef ef * Lannea aaa aac c CONTOUR INTERVAL 20 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929 2230" 22°30" 45° 15" 45° 07 112°20' 112°30' 112°2230" 30" Dillon Christensen Mine East Ranch Gulch Ashbough Elk Canyon Gulch INDEX SHOWING MAP AREA (BLUE) LOCATED WITH RESPECT TO 1:24,000-SCALE TOPOGRAPHIC BASE MAPS PLATE 1 Compiled by H. L. James, mainly from published maps by James and others (1969), James and Wier {19726}, Heinrich (1960), and Garihan (19796) DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY N4 corner sec. 25 1 I 1 *A I 7 4 ( J 1 LSeme.: IX 3, 4, 8 +, C4 A% & 80 - 85 60 I ati 18 1 * #5, "SN s /V(\\\ 60 [~ !/12(s,/ 2 ‘-L\\ §§ (a=, 4 80 60 55 ** = a 70 U/ 11 S Cal ¥ 75 ___ Center sec. 25 »w\,\\;\l\‘ tes 8 pvs 28 . (l) 200 400 600 800 ems | | | | ' | I 0 100 200 METERS TRUE NORTH APPROXIMATE MEAN DECLINATION, 1989 MONTANA «Butte Weg MAP AREA 2 ty a £.) 33:75 *BEND IN SECTION W/cm >~I'\ ~ \ Wycqg hal we *** x4 7000 - “fly A "’°’:‘~’~,>~\ j\\:x *j 357 ‘,4" a A> sa p Lu wo * _] 2 te € 3 € € p € - « 2 > © Lu 'a jar u 6000 - GEOLOGIC MAP OF THE KELLY IRON DEPOSIT, MADISON COUNTY, MONTANA Secs. 23, 24, 25, and 26, T. 6 S., R. 5 W. 1000 FEET | CE GG P Co V- 1445 PROFESSIONAL PAPER 1495 PLATE 2 CORRELATION OF MAP UNITS } PALEOZOIC Unconformity [/XWog Sxwad EARLY PROTEROZOIC AND (OR) LATE ARCHEAN LATE OR MIDDLE ARCHEAN LATE OR MIDDLE ARCHEAN ( o|C --* 20 DESCRIPTION OF MAP UNITS [Modified from James and Wier, 1972a) Paleozoic strata-Cambrian Flathead Quartzite and Wolsey Shale at north margin; limestone of Mississippian Madison Group at west margin Pegmatite (Early Proterozoic(?) and (or) Late Archean)-Pink to white, coarse grained; mostly microcline and quartz. Some small bodies not shown Quartz diorite (Early Proterozoic(?) and (or) Late Archean)-Fine to medium grained, weakly to moderately foliated Ultramafic rock (Late or Middle Archean)- Heavy, compact; dark on fresh break, weath- ers yellowish brown. Some small bodies not shown Christensen Ranch Metamorphic Suite (Late or Middle Archean) Quartzite-Micaceous quartzite, biotite-garnet quartzite, vitreous quartzite Banded iron-formation-Two or more beds Gneiss-Dark-gray, layered diopside-horn- blende-garnet-plagioclase gneiss, containing thin beds of quartzite Main iron-formation of area Quartzite and gneiss-Upper part garnet- rich; lower part poorly exposed, mainly micaceous quartzite Dolomitic marble-Medium- to coarse-grained. Upper part contains phlogopite and serpen- tinized forsterite Contact Fault-Dashed where approximately located or inferred. Relative motion shown by arrows if dominantly horizontal, by letter symbol if dominantly vertical (U, upthrown; D, down- thrown) Strike and dip of layering in metasedimentary rocks and bedding in younger strata- Overturned bedding not separately distin- guished Inclined Vertical Bearing and plunge of linear feature, such as minor fold axis, mineral orientation, or rodding