V ‘7: .. L 0/5546 6’4 :‘M m \ a ‘ fig; 7b LAYAreal Geology of the 6:31 LIBRARY P/ajé fi/A/D I'lV Western Mojave Desert W" California L9” GEOLOGICAL SURVEXJ PROFESSIONAL PAPER/522 AREAL GEOLOGY OF THE WESTERN MOJAVE DESERT CALIFORNIA 26237 Fossiliferous terrestrial beds of Miocene Bar- Beds dip into axis of major Light-colored hills beyond amphitheater eroded from pyroclastic Hills in background are mainly Mesozoic plutonic rocks overlain by Plio- Aerial View looking northwest over the Mud Hills, 9 miles north of Barstow. stow Formation are partly capped by dissected older alluvium. Rainbow Canyon is at lower right. syncline with axis across amphitheater of Rain‘bow Canyon. rocks of lower Miocene( '3) Pickhandle Formation. cene(?) andesite and Pleistocene basalt. Goldstone dry lake is at upper right. Areal Geology of the Western Mojave Desert California By THOMAS W. DIBBLEE, JR. GEOLOGICAL SURVEY PROFESSIONAL PAPER 522 Contriéutim to west coast eart/zgttaée investigations UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967 V UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secre 'ary GEOLOGICAL SURVEY William T. Pecora, Directo Library of Congress catalog-card No. G For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 CONTENTS Abstract ___________________________________________ Introduction ....................................... Location of area ________________________________ Fieldwork and preparation of geologic map _________ Purpose of investigation _________________________ Acknowledgments _______________________________ Previous geologic work ______________________________ Geographic setting __________________________________ Culture and accessibility _________________________ Climate _______________________________________ Vegetation _____________________________________ Geologic setting ____________________________________ Pre—Tertiary crystalline rocks ________________________ Older dynamothermal metamorphic rocks __________ Schistose rocks _____________________________ Distribution ____________________________ Pelona Schist ___________________________ Rand Schist ____________________________ Mesquite Schist- _ _ -4 ____________________ Origin and age _________________________ Mylonitic rocks _____________________________ Gneissic rocks ______________________________ Unnamed gneissic rocks _________________ Waterman Gneiss _______________________ Origin and age _________________________ Metasedimentary rocks __________________________ Unnamed metasedimentary rocks _____________ Bean Canyon Formation _____________________ Oro Grande Formation ______________________ Fairview Valley Formation ___________________ Garlock Formation __________________________ Age _______________________________________ Metavolcanic and hypabyssal rocks ______________ Hodge Volcanic Formation ___________________ Porphyry complex __________________________ Porphyry ______________________________ Porphyritic felsite _______________________ Tourmaline-quartz—muscovite rock ________ Field relations, origin, and age ________________ Quartz latite felsite _________________________ Rhyolite aplite- ____________________________ Hornblende schist and greenstone _____________ Plutonic rocks __________________________________ Hornblende diorite and gabbro _______________ Quartz diorite___‘_______________, ___________ Ferruginous syenite _________________________ Aplitic quartz monzonite ____________________ Gneissoid quartz monzonite __________________ Biotite—rich quartz monzonite ________________ Granite and quartz monzonite ________________ Quartz monzonite ___________________________ Granite ____________________________________ Pegmatite and aplite ________________________ Hypabyssal rocks _______________________________ Quartz latite _______________________________ L” owmmquqmmmmmpmwwwmmmrfl'g FPHBPQVF“;HRHKWDIFPPVFVPWWODWWWWWOONNNNHHHHHHHF‘ wwwwwNNHHHHOO©®©©©NNWNN®VM¢©$$$WWO Tertiary sedimentary and volcanic rocks _______________ General features ________________________________ Rock units of southern and western areas __________ Palmdale, Valyermo, and Cajon Pass areas _____ San Francisquito Formation ______________ Vasquez Formation _____________________ Vaqueros Formation; ___________________ Punchbowl Formation ___________________ Crowder Formation _____________________ Anaverde Formation ____________________ Peace Valley area ___________________________ Peace Valley Beds of Crowell (1950) ______ Hungry Valley Formation of Crowell (1950) _______________________________ West Antelope Valley area _______________________ Neenach Volcanic Formation _____________ Quail Lake Formation ___________________ Oso Canyon Formation __________________ Meeke Mine Formation _________________ Rock units of central areas _______________________ Antelope Butte, Rosamond, and Mojave areas__ Gem Hill Formation ____________________ Bobtail Quartz Latite Member ___________ Fiss Fanglomerate ______________________ Bissell Formation _______________________ Castle Butte, Boron, and Kramer Hills areas___ Unnamed lower part of Tropico Group- _ _ _ Dacite _________________________________ Saddleback Basalt ______________________ Red Buttes Quartz Basalt _______________ Unnamed upper part of Tropico Group____ Limestone _____________________________ Rock units of eastern areas _____________________ Barstow area _______________________________ Unnamed sedimentary rocks _____________ Dacite _________________________________ J ackhammer Formation _________________ Pickhandle Formation ___________________ Opal Mountain Volcanic Formation _______ Barstow Formation _____________________ Lane Mountain Andesite ________________ Rock units of northern areas _____________________ Tehachapi Valley and Cache Peak areas _______ Witnet Formation ______________________ Kinnick Formation _____________________ Rhyolitic felsite ________________________ Bopesta Formation _____________________ Andesite______________-__________, ______ Horned Toad Hills area _____________________ Horned Toad Formation _________________ El Paso Mountains area _____________________ Goler Formation ________________________ Dacite _________________________________ Ricardo Formation ______________________ v VI CONTENTS Page Page Tertiary sedimentary and volcanic rocks—Continued Mineral resources .................................. 124 Rock units at northern areas—Continued Mineral deposits and rock commodities ____________ 124 Lava Mountains area _______________________ 105 Deposits and possible occurrences of borate minerals_ 124 Gray andesite porph yry _________________ 105 Discovery and mining of borate minerals ______ 124 Rhyolite felsite _________________________ 105 Geology of known borate deposits _____________ 125 Bedrock Spring Formation _______________ 105 Probable genesis ____________________________ 127 Andesite _______________________________ 108 Reserves ___________________________________ 127 Unnamed sandstone and basalt ___________ 108 Possible occurrences of other borate deposits and Quaternary sedimentary deposits and basalt ___________ 109 areas favorable to prospect _________________ 128 Older alluvium _________________________________ 109 Petroleum and gas ______________________________ 128 Black Mountain Basalt __________________________ 109 Ground water .................................. 129 Alluvium ______________________________________ 110 Movement of ground water __________________ 129 Windblown sand ________________________________ lll Efiect of faults on ground-water movement- _ _ _ 129 Plays. clay _____________________________________ 111 Ground water in pre-Tertiary rocks ___________ 129 Geologic structure __________________________________ 111 Ground water in Tertiary rocks _______________ 130 Tertiary depositional basins ______________________ 111 Ground water in Quaternary sediments ________ 130 Faults _________________________________________ 111 Ground-water reservoirs _____________________ 130 Present tectonic activity _________________________ 115 Magmatic water ____________________________ 130 Summary Of geologic history _________________________ 115 References cited ____________________________________ 130 ILLUSTRATIONS [Plates are in pocket] . . . . Page PLATE ; (SEOIOEw map 0f western MOJavc Desert, California. FIGURE 19. Juniper Flat area, northwestern San Bernar- . ap of western Moiave Desert region, showmg major . . phvsiographic and geographic features d1no Mountains """""""""""" 32 ‘ . , _ ' , 20. Black Mountain area near Sidewinder Moun- 3. Index map showmg location of detailed geologic maps tain __________________________________ 33 and sections, figures 3'69’ and explanation 0f 21, 22. Central and eastern El Paso Mountains__ 34—35, 36 symbols. ' 23. Stoddard well area _______________________ 38 4. Sequences of sedimentary and volcanic rocks of 24. Hills southwest of Mirage Lake ____________ 40 Cenozoic age exposed in western Mojave Desert. 25. Saddleback Butte area east of Lancaster" __ 44 Frontispiece. Aerial View looking northwest over the Mud Hills, 26. San Francisquito Canyon area _____________ 45 9 miles north 0f Barstow. 27. Soledad Pass area ________________________ 47 page 28. Little Rock area _____________________ _ _____ 48 FIGURE 1. Index map of southeastern California showing 29, 30. Devils Punchbowl area ____________________ 50, 51 location of western Mojave Desert region- - 2 31; 32' Caj on P335 area, northwestern part- --- - — '52-'53, 54 2. Diagrammatic section of generalized rock 33- San Gabriel Mountain foothill area near units _________________________________ 6 M6531 Creek __________________________ 55 . . . . . 34. Palm e area ___________________________ 57 3~69- Detalled geolOglc maps and sections of CI‘ltlcal 354,7. West end of Antelope Valley ____________ 59’ 60, 61 areas. , 38. Antelope Buttes area _____________________ 64 3' 4' Rind M°untams -------------- 10. 12 39,40. Rosamond Hills __________________________ 65, 66 5y 6- H1113 north 0f Bal'StOW _________ 15, 16 41. Middle Buttes __________________________ 67 7' 8‘ Iron Mountain area ——————————— 17: 18 42. Soledad Mountain area ___________________ 68 9- Hills north of Hinkley ......... 19 43. Bissell Hills area ________________________ 69 10- Hills W851i 0f Harper Valley _____ 20 44, 45. Castle Butte area ________________________ 72, 73 11. Bronco and Antelope Canyon 46, 47. Kramer borate district ___________________ 74, 75 area, Tehachapi Mountains___ 21 48. Muroc and Stone House Hills ______________ 77 12, 13. Techachapi Mountain foothills__ 22, 24 49- Kramer Juncti‘m 01” east Kramer area ------ 78 14, 15. Quartzite Mountain area _______ 26, 27 50' 51' Kramer Hills “““““““““““““““ 80’ 81 16, 17. Shadow Mountains ____________ 29’ 30 52. LenWOOd area—-___—_—_--_—__-'_-____-____ 83 18. Nor thernmos t t f S'd . d 53. Upper Black Canyon and Opal Mountain par 0 l ewm er area _________________________________ 85 Mountam ------------------ 31 54, 55. Mud Hills ______________________________ 88, 89 CONTENTS Page FIGURE 56. Northwestern and central Gravel Hills ______ 90 57. Southeastern Gravel Hills and lower Black Canyon ______________________________ 92 58. Monolith-Sand Creek area, southern Sierra Nevada ______________________________ 94 59. Cache Peak area, southern Sierra Nevada--- 95 60. Monolith and Cache Peak areas, southern Sierra Nevada _________________________ 96 61. Jawbone Canyon area, southern Sierra Nevada _______________________________ 97 62. Horned Toad Hills area ___________________ 99 63. Lower Jawbone and Redrock Canyons area, El Paso Mountains ____________________ 101 64—66. Last Chance Canyon, Black Mountains-Goler Gulch, and Redrock Canyon areas, El Paso Mountains ______________________ 102, 103, 104 67. Red Mountain area _______________________ 106 68. Summit Diggings area ____________________ 107 69. Sand Hills ______________________________ 110 70. Bouger anomaly and generalized geologic map _________________________________ 112 TABLES FIGURE 71. Probable areal extent of depositional basins filled with sedimentary and volcanic rocks of Tertiary age and their inferred profiles and depths ____________________________ 72. Simplified geologic map of San Andreas fault zone at margin of Mojave Desert, showing evidence suggesting right lateral displacements, measurable in miles, on San Andreas fault and its branches ______ 73. Tectonic map ___________________________ 74—80. Paleogeographic maps—Tertiary through Pleistocene time. 74. Paleocene and Eocene ____________ 75. Oligocene(?), early, and early middle Miocene ________________ Late middle and late Miocene _____ Pliocene ________________________ Beginning of Pleistocene __________ Pleistocene ______________________ End of Pleistocene _______________ 76. 77. 78. 79. 80. [Tables 2—4 follow “References cited”] TABLE 1. Divisions of Tropico Group in western Mojave Desert and their presumed correlations__-_ 2. Tabulated list of borate mines ______________ Page TABLE 3. Exploratory test holes drilled for min/erals____ 63 137 4. Exploratory test wells (drilled for oil and gas) and geological significant water wells ______ VII Page 113 114 116 117 118 119 120 121 122 123 Page 138 148 AREAL GEOLOGY OF THE WESTERN MOJAVE DESERT, CALIFORNIA BY THOMAS W. ABSTRACT The western Mojave Desert is in Kern, Los Angeles, and San Bernardino Counties. In this 7,000—square—mile region are the towns of Gorman, Palmdale, Lancaster, 'R'osamond, Mojave, Randsburg, Boron, Barstow, and Victorville. The center of the region is about 70 miles north-northeast of Los Angeles. The western Mojave is a wedge-shaped area, bordered on the southwest and northwest by rugged mountain ranges that reach altitudes of 10,080 and 7,900 feet above sea level, respectively. The desert itself has comparatively low relief, and is virtu- ally an alluviated plain containing irregularly trending bedrock hills and low mountains. The alluvial are-a contains seven undrained dry lakes or playais in the lowest parts. The only through-going drainage channel is that of the Mojave River— ‘an intermittent river that flows from the lofty San Bernardino Mountains northward, and then eastward, out of the mapped area. The alluviated desert plain ranges from altitudes of about 4,000 feet adjacent to the bordering mountains to about 2,000 feet at the playa flats and along the Mojave River channel. The bedrock areas within the desert region rise to generally not more than 1,500 feet above the surrounding alluviated flats, although the highest peak rises to about 2,400 feet above them, or to an altitude of about 5,200 feet above sea level. The rocks of the western Mojave Desert region and the bor- dering mountains may be grouped into three main divisions: (1) crystalline rocks of pre-Tertiary age; (2) sedimentary and volcanic rocks of Tertiary age; and (3) sediments and local ‘ basalt flows of Quaternary age. The crystalline rocks are largely plutonic, and there are some isolated pendants of metamorphic rock. The crystalline rocks may be grouped into four major divisions: (1) older dynamothermal metamorphic rocks; (2) metasedimentary rocks; (3) hypabyssal and metavolcanic rocks; and (4) plu- tonic rocks. The older dynamdthermal metamorphic rocks are divided into three units: schistose rocks, mylonitic rocks, and gneissic rocks. They are unfossiliferous and presumably are of Precambrian age. The metasedimentary rocks are assemblages of carbonate rocks, phyllites, schists, cherts, quartzites, and conglomerates of marine origin, and minor mafic to andesitic flows. Meager fossils found in a few assemblages indicate late Paleozoic age. The hypabyssal and metavolcanic rocks are porphyritic and aphanitic intrusives and extrusiveus of mainly Mesozoic age in the eastern part of the desert region. The plutonic rocks are granitic-textured intrusives that range in composition from hornblende diorite and gabbro through quartz diorite and quartz monzonite to granite. Quartz mon- zonite is by far the most prevalent type; it forms the south- east extension of the Sierra Nevada batholith through the west- DIBBLEE, JR. ern Mojave Desert. Lead-alpha age determinations indicate a range from 90 to 96 million years, or Cretaceous age, for this rock. The sedimentary and volcanic rocks of Tertiary age include conglomerates, sandstones, shales, carbonates, tufts, breccias, and lava flows and plugs ranging in composition from rhyolite to basalt. These rocks rest upon a deeply eroded surface of the crystalline rocks from which the elastic rocks were largely derived. Rapid lateral changes in lithology and thickness of stratigraphic assemblages of the Tertiary rocks indicate depo- sition during tectonic activity. The oldest Tertiary stratigraphic units are clastic sedimen- tary rocks of early Tertiary age and are known only in the mountains that border the desert region. Terrestrial units of Oligocene to middle Miocene age are mainly volcanic rocks of rhyolitic to andesitic composition, in large part pyroclastic, and minor sedimentary rocks and mafic flows. Units of late Mio- cene age are nearly all sedimentary, except for some andesitic intrusions and flows in the northwest-bordering mountains. With the exception of a marine and brackish-water formation at the west end of the desert region, all the sedimentary units in the desert are nonmarine and range from coarse stream-laid sediments to lacustrine shales and minor chemical sediments. Units of Pliocene age are all nonmarine; they are sedimentary in southern parts of the mapped area, sedimentary and volcanic in northern parts. Nearly all units include both stream-laid and lacustrine strata. The sediments of Quaternary age are mainly alluvial depos- its that fill the major part of the desert region. They range from coarse fanglomerate to fine clay derived from the moun- tains that border the desert region and from the highlands within it. In most places these sediments rest unconformably on rocks of Tertiary and pre-Tertiary ages, but in some places are conformable on Tertiary sedimentary rocks. The structure of the metamorphic rocks within the mapped area is complex ; prior to the invasion of the plutonic rocks they were severely folded, upturned, and in places thrust faulted. In the desert region, structural trends in these rocks are erratic, but are predominantly west to northwest in the northwest- bordering mountains, mostly west in the southwest-bordering mountains. The western Mojave Desert region is a tectonic block—known as the Mojave block—bounded on the southwest by the San An- dreas fault zone and on the northwest by the Garlock fault zone, along which the bordering mountains were elevated. Both zones are vertical crustal breaks along which major displace- ments are strike slip or lateral. Total cumulative right-lateral movement 011 the San Andreas fault zone in this region may be about 50 miles, and left-lateral movement on the Garlock fault zone about 17 miles, possibly as much as 30. 2 AREAL GEOLOGY, WESTERN MOJ'AVE DESERT, CALIFORNIA The Mojave block is also broken by several major high-angle faults, most if not all active during Quaternary time. They generally trend northwest, form low scarps if any at all, are characterized by reversals of (apparent) vertical displacements, and show evidence in several places of small right-lateral dis- placements. Some faults trend northeast; most of these are north-dipping normal faults. Tertiary formations exposed throughout the area are strongly deformed, either by tilt or by compression into folds having west-trending axes. They are most severely deformed adjacent to the major faults that have lateral displacement. Quaternary formations are deformed in the same manner but to less degree. Alluvium-covered parts of the Mojave block are underlain by several large basins or downwarps that contain as much as 10,000 feet of Cenozoic sedimentary fill. The Cenozoic forma- tions are presumably undeformed in the central parts of most of these basins. The major domestic source of boron compounds is a single large deposit of sodium borate near the town of Boron. This deposit is in lacustrine shale of the upper (middle Miocene) part of the Tropico Group. The lacustrine shale is practically devoid of other saline minerals. The source of the borate min- erals is presumably volcanic thermal springs genetically related to basalt flows that underlie the shale. The small marginal and outlying deposits are mostly of calcium borate. 119° 118° 117° INTRODUCTION LOCATION OF AREA The Mojave Desert in southeastern California is a wedge-shaped region having its apex toward the west. This report deals with the western part of the desert—— a part that is characterized by interior drainage and is sharply delineated by mountain ranges on both the southwest and northwest. The part mapped geologi- cally includes about 7,200 square miles between lat- itudes 34°34’ and 35°30’ N. and longitudes 117° and 119° W., or parts of Kern, Los Angeles, and San Ber- nardino Counties. The center of the region lies about 70 miles airline north-northeast of Los Angeles (fig. 1). FIELDWORK AND PREPARATION OF GEOLOGIG MAP Fieldwork was done during the spring, autumn, and winter months from 1952 to 1955 and during short intervals from 1956 to 1959. The geology was plotted in the field on aerial photo- graphs at scales between about 1:48,000 and 1 :25,000, 116° 115° L. S TULARE \I \ 36“ | 0 50 MILES N ’/\--/‘ JKERN BERNARDI \; Bakersfield {29:1 >'0 U '2. .1... I?” \ 35° m” // \} "”/////////////, R / \ ANGELES ) ’ ‘ i [/‘J . Pasadena 1 M Angeles ./ 1— 34° 1— (O4 0’» f 0 FIGURE 1.—Index map of southeastern California showing location of western Mojave Desert region. PREVIOUS GEOLOGIC WORK 3 and was subsequently transferred to 15-minute 1:62,- 500-scale topographic quadrangle base maps as these became available. An average of about 1 month was required to map the geology of each quadrangle and about another month was required to transfer the geology from aerial photographs to the quadrangle base map. Geologic maps of fifteen 15-minute quad- rangles (pl. 1, index to topographic maps) were pub- lished prior to completion of this report (Dibblee, 1958a, b; 1959a, b; 1960a—g; 1961b; 1963). Published maps of areas studied by other geologists (pl. 1, index to geologic maps) were field checked and, where neces- sary, were remapped by the writer before incorporation in this report. All data were recompiled at a scale of 1:125,000 (pl. 1). PURPOSE OF INVESTIGATION This report and map (pl. 1) represent part of a geologic investigation by the US. Geological Survey of the known and potential deposits of borate minerals in the southern California desert regions. The primary purpose of this report and the geologic map (pl. 1) is to provide a geologic background for the exploration for possible concealed borate deposits in the western M0- jave Desert, based upon (1) the geology of the known deposits of these minerals within the region, (2) the areal geology of the region, and (3) the subsurface geology as determined insofar as possible from logs of exploratory test holes, mine workings, and geophysical data. Available logs of test holes so used, including those drilled for petroleum and some for water, and of borate mine shafts are summarized in tabulated form (tables 2—4); the gravity geophysical data are published separately (Mabey, 1960). The resulting geologic data are of use for many sec- ondary purposes, such as exploration for other com- modities, including petroleum and gas, and in evalua- tion of ground-water conditions. The base for the geologic map was prepared by join- ing parts of the Bakersfield, Trona, Los Angeles, and San Bernardino quadrangles, as published by the US. Geological Survey at a scale of 1:250,000, and then enlarging the mosaicked map to a scale of 1:125,000 (1 inch=2 miles). Although lacking in detail and accuracy, the base is the best that is available. Numer— ous maps at a scale of an inch to a mile or larger show the geology of most of the complex areas in greater detail. ACKNOWLEDGMENTS The writer is particularly indebted to the following members of the US. Geological Survey: D. F. Hewett for his unfailing interest in the work and for the aerial photographs used in mapping, W. C. Smith for his technical advice and direction, K. E. Lohman, for work on fossil diatoms in the area; G. E. Lewis, for work on the vertebrate fossils from the Mud Hills and Black Canyon, and R. D. Allen for modal analyses of the igneous rocks. Mr. D. J. Ryan, geologist for Kerr—McGee Oil In- dustries, Mr. R. G. Maynard, geologist for Sunray- Mid-Continent Oil 00., Mr. K. M. Reim, geologist for Kern County Land 00., and Mr. S. J. Muessig, geologist for United States Borax and Chemical Co. (since 1957), have furnished logs of many prospect holes drilled for borates in the region. The investigation was supported in part by funds from the Bureau of Aeronautics, US. Navy. PREVIOUS GEOLOGIC WORK The earliest descriptions of the geology of the west- ern Mojave Desert and the mountains along its south- western margin are by Hershey (1902a, b). In his first report he described the pre—Tertiary crystalline rocks; in his second, the Tertiary sedimentary and volcanic rocks. He discussed probable correlations, named several formations, and prepared a geologic sketch map. The Tertiary rocks were further described by Baker (1911, 1912), and their fossils were described in sev- eral papers by Merriam (1911, 1914, 1915, 1919). Pack (1914b) did a reconnaissance and discussed the oil possibilities of the Harper Valley area between Barstow and Kramer. He also presented a geologic map—the first in the western Mojave Desert. Darton (in Darton and others, 1915) described the rocks of the Barstow-Victorville area. The ground—water resources of Antelope Valley were described by Johnson (1911). This report was fol- lowed some years later by an exhaustive study by Thompson (1929) of the ground-water conditions of the entire Mojave Desert; Thompson’s report includes a reconnaissance geologic map of the desert region. Hulin (1925) described the geology and ore deposits of the Randsburg 15-minute quadrangle in a report which included a 1:62,500-scale quadrangle geologic map—the first one in the Mojave Desert. Similar reports and geologic maps of other quadrangles and areas within the western Mojave Desert followed. Among these were reports by Simpson (1934) on the Elizabeth Lake (30-minute) quadrangle; Gardner (1940) on the Newberry and 0rd Mountains; Gale (1946) on the Kramer borate district; Wallace (1949) on the San Andreas fault zone west of Palmdale; Crowell (1950 and 1952) 011 the Gorman-Hungry Valley area, and on the Lebec (71/2-minute) quad- rangle; Wiese ( 1950) on the Neenach quadrangle; 4 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Dibblee (1952) and Dibblee and Gay (1952) on the Saltdale quadrangle; Noble (1953 and 1954a) on the Pearland and Valyermo (6-minute) quadrangles; Bowen (1954) on the Barstow (30-minute) quad— rangle; Troxel (1954) on the northwestern Shadow Mountains; and Dibblee (1967) on the Fremont Peak and Opal Mountain quadrangles. The locations of these published geologic maps are shown on the index map on plate 1. In addition, several reports and generalized geologic maps of parts or all of the western Mojave Desert have been published by Miller (1944) on the geology of the Barstow, Hinkley, and Oro Grande areas; Wiese and Fine (1950) on the geology of west Antelope Valley; Hewett (1954a and 1954b) on the general geology of the Mojave Desert and on the faults of the Mojave Desert; Buwalda (1954) on the geology of the Teha- chapi Mountains; and Noble (1954b) on the geology of the San Andreas fault area between Cajon Pass and Soledad Pass. The locations of most of these areas are also shown on the index map on plate 1. GEOGRAPHIC SETTING CULTURE AND ACCESSIBILITY Except in scattered towns (pl. 1), the western Mo- jave Desert region is virtually uninhabited. The larg— est towns in the area, according to the 1960 census, are Barstow, with about 10,000 inhabitants; Victorville, with about 8,000; Lancaster, with about 25,000; Palm- dale, with about 10,000; and Edwards, with about 5,000. The area is traversed by several major highways, and many paved, gravel, and dirt roads; these make all parts of the region accessible by road. The region is also traversed by several lines of the Southern Pacific Railroad and the Atchison, Topeka, and Santa Fe Railway. Several military installations prohibit or restrict travel locally. The principal physiographic and geographic features of the western Mojave Desert are shown on plate 2. CLIMATE The Mojave Desert is characterized by arid climate and a wide range of seasonal and daily temperatures. Maximum summer temperatures commonly exceed 100°F. Minimum winter temperatures fall below freezing, sometimes to 5°F. Diurnal temperature changes commonly exceed 50°F throughout the year. Average annual precipitation ranges from less than 5 inches in the interior parts to more than 40 inches on the crest of the San Gabriel Mountains. Most precipitation comes from Pacific cyclonic storms that pass eastward over the region from November to April. Generally the storms bring rain or snow in the moun- tains, but only a few bring rain to the desert because of the drying effect of the bordering mountains on the moisture-laden air descending their leeward slopes. Nearly all storms are accompanied or followed by gales that blow over the Tehachapi and Sierra Pelona Mountains and eastward across the desert region, com- monly with enough force to carry dust and sand in the desert. Occasionally during the late summer months thun- derstorms bring heavy showers or cloudbursts. These storms result in flash floods and cause severe erosion locally. VEGETATION Vegetation in the desert region is of the sagebrush type and consists of scattered but evenly spaced plants. mostly creosote bush and burro bush. Grasses and flowering annuals grow only in spring after unusually heavy winter rains. The vegetation is generally uni- form, the underlying rock formations having little influence upon it. Giant yuccas (Joshua trees) are common on sandy flats and alluvial slopes between altitudes of 2,800 and 4,000 feet. Cottonwoods and some willows grow along the permanent streams. The playa-lake beds are devoid of vegetation. Mountain slopes facing the desert between altitudes of 4,000 and 6,000 feet are partly covered with chapar- ral consisting mainly of scrub oak, chamiso, manzanita, juniper, pifion pine, and yucca. Above 6,000 feet the mountains are forested with oak, sugar pine, and some cedar. GEOLOGIC SETTING The Mojave Desert region is geologically a great wedge-shaped fault block, called by Hewett (1954a, p. 16—17, 1954b, p. 5) the “Mojave block.” It is bounded by the San Andreas and Garlock fault zones on the southwest and north, respectively, but has no definite natural eastern limits. Both fault zones are continuous, generally vertical, crustal breaks having lateral displacements measurable in miles. Of these two master shear zones, the San Andreas fault zone is by far the larger, having a known length of at least 600 miles and a possible cumulative right-lateral dis- placement of as much as 350 miles (Hill and Dibblee, 1953, p. 449). The mountain ranges elevated along the San Andreas fault zone separate the Moj ave Desert from the coastal area to the southwest. The Garlock fault zone, though subordinate to the San Andreas fault zone in length and magnitude of displacement, is nevertheless a master shear zone that is traceable for some 150 miles and has a left-lateral displacement of unknown magnitude. This fault separates the Mojave block‘ from the Sierra Nevada- GEOLOGIC SETTING 5 Tehachapi Mountain uplift and the Basin and Range province to the north. The Mojave block itself is broken by many major but discontinuous faults, as shown on plate 1. These appear to be generally vertical to steep shear zones having predominantly lateral displacements of rela- tively small amounts. In the mapped area (pl. 1), these faults trend northwest, and displacements on some are right lateral, as on the San Andreas. How- ever, in the northeastern part of the Mojave block, the faults trend predominantly east; some show evidence suggestive of left-lateral displacement. Many of the faults bound or partly bound desert mountain ranges and valleys; others transect them. (For a map show- ing the geologic setting of the western Mojave Desert, see Dibblee, 1960d, pl. 7, or 1963, pl. 11.) In the western Mojave Desert region and adjacent mountains, the rocks may be grouped into the follow— ing three main divisions: (1) crystalline rocks of pre- Tertiary age, (2) sedimentary and volcanic rocks of Tertiary age, and (3) sediments and local basalt flows of Quaternary age. A generalized section of the rock units of the western Mojave Desert is shown diagram— matically on figure 2. The pre-Tertiary crystalline rocks may be grouped into the following four major divisions based largely upon their lithologic characteristics: (1) older dyna- mothermal metamorphic rocks, (2) metasedimentary rocks, (3) hypabyssal and metavolcanic rocks, and (4) plutonic rocks. Of these major rock units the plutonic rocks are by far the most extensive, in which the older metamorphic and the metasedimentary rocks occur as isolated roof pendants. The older dynamothermal metamorphic rocks are schists, mylonites, and gneisses; they are unfossilifer— ous and presumably of Precambrian age. The meta- sedimentary rocks are assemblages of carbonates, phyl- lites, schists, cherts, quartzites, and conglomerates of marine origin. Meager fossil remains indicate late Paleozoic ages. The hypabyssal and metavolcanic rocks are porphyritic and aphanitic intrusives and extrusives associated with the metasedimentary and plutonic rocks, and they range in age from Paleozoic to‘early Tertiary, but are mainly Mesozoic. The plu- tonic rocks are widespread granitoid-textured (hypau- tomorphic) intrusives ranging in composition from granite to gabbro, but are predominantly quartz mon- zonite; they are mainly if not entirely of Mesozoic age. The sedimentary and volcanic rocks of Tertiary age are predominantly of terrestrial origin and include conglomerates, sandstones, shales, carbonate rocks, si- licic tufi's and breccias, and lava flows and plugs rang- ing in composition from rhyolite to basalt. Stratified assemblages of these rocks are characterized by rapid lateral changes in lithology and thickness that indicate deposition in local intermontane basins during times of tectonic activity. The sediments of Quaternary age consist mainly of alluvial deposits that fill the intermontane areas of the Mojave block and the small valleys in the adjacent mountains. The deposits range from a few feet to several hundred or possibly several thousand feet in thickness. The sediments were derived from the ad— jacent mountains and hills and vary from coarse fanglomerates to fine clays. In most places they rest unconformably on rocks of pre-Tertiary or Tertiary age; in a few places they appear to grade downward into the Tertiary rocks. The Quaternary deposits are divided into (1) older alluvium of Pleistocene age, which is locally tilted, deformed, and dissected; (2) dissected terrace deposits of late Pleistocene age that occur locally; and (3) younger undissected alluvium of Recent age that fills all modern valleys and covers the flood plains. In the northeastern part of the region, the older alluvium contains at least two local basalt flows that range from a few feet to as much as 300 feet in thickness. The rock units that occur in the area are described in the following pages. Units of the pre-Tertiary crystalline rocks and the Quaternary sediments and basalt are generally widespread and are described in chronologic order from oldest to youngest. However, because units of the Tertiary volcanic and sedimentary rocks are of limited areal extent and of uncertain cor- relation, local sequences as indicated on plate 1 are described separately. To conserve both time and space, descriptions of the units have been written in telegraphic style. Accompanying the description of each rock unit or local sequence is a geologic map of a critical area at a scale of 1 inch to the mile or larger, with one or more cross sections, to show lithologic and structural detail not shown on plate 1. The positions of these large- scale maps of small areas are indicated on plate 3, together with the symbols used on the maps. The rock sequences exposed in some of these critical areas are shown on plate 4. PRE-TERTIARY CRYSTALLINE ROCKS OLDER DYNAMOTHERMAL METAMORPHIC ROCKS A large part of the pre-Tertiary crystalline complex of the western Mojave Desert region is made up of intensely metamorphosed rocks composed of gneiss, schist, and some mylonite. These rocks crop out mostly in the mountains along the southwestern and north- AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA .fiwmon SE32 5833 no BE: Moon dcfififienow yo H8325 oEaEEEmfiQIN mascara SMDOH AHVILHEL'EHd 33190.4 mudwommaw 3:190; afmomld SMOOH AHVNHELVDO ONV AHVILHEJ. 391 90.; ammo/1 1 7147.4me 99190.4 Minus m’gpag 54¢an amium I.) 1. \/ \ z \ $3.5 \\zl“ / \ \\(>\ _ I x / x j 53?. ”FIN” Ewa=w5_vwmda®2 »\ A < < 530.— Emmhnanhn x. < “Eu o_:uo_o>5w5 V v > 93.1% E; 85% 3.53:3: 3131 55:0 u t “ 31360.35 «Ea . 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(37314529 pm) 9149903 AHVLLHEJ. a..Im-......--..........u-- (DIOZOSEW 0i tNVlafiWVDEHd) AHVILHEi‘EEd l . n.-u ..... o.-|uoo.lo.-o ......... .\.00|0|Illo IIIIII on..-na uuuuu on llllll ooooocoo0000.1I-noo-conu1000 n... QIIIIO.0 0.00.000..I0.000 .:0 av. :-|.IIVIIaoooon. 0000 O oonolooO-.O o o 0000...0 a a o o n .. I ‘ - ==_=-.-..==. —===ouonuooa no ooooonoou o o coo a o-Oo.o ouc.nu.ouo.ouo.n.o.c I 0.. . . .000.o.|u-.:. llllll ooo onooooooo ||.| ooooOoWIu;.a.-‘.o.o..o.. a0 no no . II 00000 .7 e 000000000000 OuOOOMOBMWWoOOoou enooo.ooe-o».o voloo allel|.a.o....0u ..... Oo.o... IIO .-I|«|1‘uluu:|| Olooo ................ o |.:.|.n4.....:.....l..|l ..o 1.33.! 000‘9'! ”99038191,; AHVNHELVHO guaosg FEE-TERTIARY CRYSTALLINE ROCKS 7 western borders and locally in the eastern and north- ern parts of the desert. Because the age relationship of the older metamor- phic rocks is controversial, these rocks are described in the order of their present physical positions, which in ascending order is: (1) schistose rocks, (2) mylonitic rocks, and (3) gneissic rocks. SCHISTOSE ROCKS DISTRIBUTION Schist known by local names but here referred to collectively as one major unit under the term “schistose rocks.” Exposed south of San Andreas fault in east- ern San Gabriel Mountains and Sierra Pelona, and north of it at Portal Ridge; also along or near Garlock fault zone in Tehachapi, El Paso, and Rand Moun- tains (pl. 1). Rocks are described below under their local names for each area after a general overall de- scription of their lithology. Schistose rocks dark-bluish to greenish gray; weather gray, yellowish gray, or brown; fine to medium grained ; rich in mica or other flaky minerals having parallel orientation; highly foliated, silvery sheen on foliation ' planes. Foliation parallel to bedding generally, as indicated by color and compositional variations of schist layers and by thin layers of marble and quartz- ite parallel to foliation of schist. In few places, how— ever, foliation passes through contorted bedding where seen. Schistose rocks composed of several varieties. Highly foliated gray schist essentially of muscovite, plagio- clase, and quartz most widespread; plagioclase (gen- erally albite, rarely oligoclase) scattered as subhedral and anhedral white porphyroblasts, 1/2—2 mm in size, gives schist granular appearance, forms 10—75 percent of the rock, averages about 30 percent; colorless mus- covite in small flakes less than 1-mm average diameter, parallel and subparallel with foliation, bent around porphyroblasts of plagioclase, forms 10~25 percent of rock; flakes of golden-brown biotite and brownish-green chlorite commonly associated with muscovite; quartz forms minute grains generally concentrated in small lenticular patches or layers 1—2 mm thick along foliation planes, forms 10—30 percent of the rock. As proportion of biotite or chlorite increases, gray muscovite-albite schist grades into dark-lead-gray bio- tite-albite schist and dark-greenish-gray chlorite schist, respectively; highly foliated. Chlorite-bearing gray schist grades into green schist composed essentially of chlorite, amphibole (actinolite, some green hornblende), and plagioclase (albite, rarely oligoclase) , in varying proportions, and small percent- ages of epidote (clinozoisite, allanite) , magnetite, limo- nite, and pyrite; most of plagioclase forms augenlike porphyroblasts generally 2—3 mm locally as large as . 5 mm in diameter, set in a dark-greenish fine-grained groundmass formed by other minerals. Green schist well foliated to “knotty” with crude lineation. Actinolite schist commonly associated with green schist as lenses or .iregular masses few feet or tens of feet wide; composed of apple-green. fibrous aggregate of aetinolite, in places with veinlike deposits of epidote and quartz; in places altered to talc schist. In some exposures, marble and quartzite occur as thin layers from few inches to several feet thick inter- calated in gray schist parallel to foliation; in zones as thick as 150 feet and as long as several hundred feet. Marble, bedded, white to light—blue gray, fine grained, calcitic; in places contains dark-gray graphitic lam- inae. Quartzite, gray White to pinkish gray, some stained brown or black from manganese oxides, very fine grained, commonly micaceous. White quartz present in nearly all exposures of schistose rocks as scattered lenticular veins few inches or feet thick and few feet or tens of feet long; many veins parallel to, others discordant to, foliation of enclosing schist, rarely if ever contain minerals of economic value. PELONA scmsr Pelona Schist of Sierra Pelora.—Schistose rocks of Sierra Pelona first examined and described in 1853 by Blake (1857, p. 59—60), later described as Pelona schist series by Hershey (1902a, p. 27 4—27 7 ) ; areal extent and geologic structure first mapped by Simpson (1934, pl. 5) ; section exposed in Bouquet Canyon area, mapped and described in more detail by Muehlberger (1958) and Muehlberger and Hill (1958); also mapped by writer (Dibblee, 1960c, 1961b). Pelona Schist of Sierra Pelona folded into a double anticline as indicated by-foliation attitudes (pl. 1), which exposes about 7,500 feet of schist; base un- exposed. Sequence mainly gray schist; contains lesser amounts of intercalated green schist that becomes increasingly abundant downward and predominates in lowest part. Small occurrences of actinolite schist and talc schist locally; few thin layers of marble and quartzite in middle and upper parts. On south flank, top of schist separated by few tens of feet of cata- clastic and mylonitic rocks from aplitic quartz mon- zonite that contains inclusions of gneiss. Pelona Schist of Portal Ridge—Schist of Portal Ridge first described by Johnson (1911, p. 23—24); included in Pelona Schist by Simpson (1934, pl. 5) and Wallace (1949, pl. 1, p. 7 81—808). Crops out in a narrow strip between the San An- dreas fault and the Hitchbrook fault to the north. Schist dips north as indicated by foliation attitudes; 8 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA about 6,000 feet of schist exposed. Differs from schist of Sierra Pelona in being darker and having biotite rather than muscovite as predominant mica. Schist gray; composed essentially of biotite, plagio- clase (albite), and quartz. Some contains muscovite, chlorite, epidote (clinozoisite, pistacite), amphibole (actinolite, green hornblende). Sequence texturally uniform; biotite most abundant in lower part, albite in upper part. Schist contains several thin lenses of micaceous quartzite stained brown by oxides of iron and manganese; several diabase dikes in sec. 13, T. 6 N., R. 13 W. Pelona(.?) Schist of Quartz Hill.—Schist at Quartz Hill (about 5 miles southwest of Lancaster) included in Pelona by Simpson (1934, pl. 5). Schist dips north as indicated by foliation attitudes, about 1,000 feet exposed; much coarser than in other exposures; composed essentially of biotite, plagioclase (andesine), and quartz; minor amounts of muscovite, epidote (clinozoisite), and iron oxides, including hema- tite; rock homogeneous and texture intermediate be- tween that of schist and quartz diorite; average grain size 1—2 mm. Pelona Schist of eastem San Gabriel Mountains and Cajun Pasa—Schist of Cajon Pass first noted by Blake (1857, p. 88); correlated with Pelona Schist of Her- shey (1902a) by Noble (1926b, p. 28—29, 31) ; described and mapped as Pelona Schist by Noble (1932, p. 11—12; 1954a; 1954b, p. 42—43), in detail by P. H. Ehlig.1 Pelona Schist occurs southwest of San Andreas fault; divisible into two blocks separated by Punch- bowl fault (pl. 1) ; northern block referred to as Blue Ridge block, southern block as San Gabriel Moun— tain block. Extends far southeast beyond border of map. Schist of Blue Ridge block folded into tight west- plunging anticline Whose north flank is partly over— turned and faulted out southeast of Wrightwood as indicated by foliation attitudes (pl. 1); about 8,000 feet of schist exposed; lithologically identical to that of Sierra Pelona; gray schist predominant over green schist; minor, very thin beds of quartzite and marble; occasional small masses of coarse actinolite, rare masses of talc schist; no granitic, aplitic, or diabasic dikes found. Pelona Schist of San Gabriel Mountain block ex- tends southeast beyond border of mapped area; arched into large northwest-plunging anticline (pl. 1) in which about 10,000 feet of schist is exposed; lowest exposed part mainly gray schist, upper part mainly lEhlig, P. H., 1958, Geology of the Mount San Antonio area, San Gabriel Mountains, California: California Univ. at Los Angeles, Ph.D. thesis. green schist, grades upward into overlying mylonitic rocks. Differs from schist of Blue Ridge block in having somewhat more biotite; in scarcity of marble beds, actinolite and talc schist; and in presence of many sills and dikes of aplitic to granophyric quartz monzonite and some of diabase; near intrusive contact with quartz monzonite to southeast schist becomes sub- gneissic with increasing amounts of hornblende. Pelona Schist of Tehaclzapi Mountains.—In Teha- chapi Mountains, schistose rocks referred to Pelona Schist (of Hershey) by Wiese (1950, pl. 1, p. 12—15). Schist crops out as a narrow strip bounded by bifur- cations of the Garlock fault zone (pl. 1); about 5,000 feet exposed. Foliation strikes north of east parallel to boundary faults, generally vertical. Gray schist predominates over green schist; contains some thin layers of quartzite, a few small pods of actinolite schist and actinolite-talc schist. RAND SCI-HST Rand Schist of Band Mountains.—Schistose rocks of Rand Mountains described briefly by Hess (1910, p. 28—29, 46) and by Hershey (1902a, p. 273); named, described, and mapped as Rand Schist by Hulin (1925, p. 23—31, pl. 1), and officially adopted for use in this report. Rand Schist folded into anticlinal arch plunging gently westward as indicated by foliation attitudes (figs. 3, 4). On north, schist overlain by gneissic rocks (Johannesburg Gneiss of Hulin), separated by possible fault or thin zone of cataclastic( ?) transition- al rock; on south and near Randsburg, schist intruded by quartz monzonite; extends unknown distance west- ward under alluviated valley, possibly to Garlock fault. Possibly 10,000 feet of schist exposed; lithology iden- tical to that of Pelona Schist of Sierra Pelona and of Tehachapi Mountains; gray schist, predominating over green schist, contains occasional pods of fibrous actino— lite schist; thin layers of quartzite and of marble, mostly in southern and western exposures. In expo- sures northeast of Johannesburg, albite content of schist increases to 75 percent. Type locality of Rand Schist designated as generally north-dipping section in Rand Mountains (fig. 4), from quartz monzonite intrusion just south of Rands- burg northward to contact with overlying( ?) gneiss about 3 miles north of Randsburg. museums scmsr Mesquite Sehist of El Paso Mountains.—Schistose rocks in Mesquite Canyon, El Paso Mountains, de- scribed and mapped as Mesquite Schist by' Dibblee (1952, p. 14—15), and term officially adopted for use in this report. FEE-TERTIARY CRYSTALLINE ROCKS 9 Schist dips east, in contact with gneissoid quartz monzonite to west, overlain unconformably by Garlock Formation (figs. 21,- 22); about 4,500 feet of schist exposed. Mesquite Schist highly foliated, dark gray; com- posed essentially of finely divided muscovite or seri- cite, chlorite, and scattered minute porphyroblasts of plagioclase (albite) and quartz; foliation planes mottled with numerous minute dark-gray clusters of chlorite and quartz; some clusters contain grains of chloritoid; in one place clusters contain remnants of cordierite (R. L. Christiansen, oral commun., 1961). Finely crystalline gray-white calcitic marble occurs sporadically throughout schist as lenses parallel to foliation, from few inches to 10 feet thick; mostly in upper part of schist. Marble strata in lowest part of schist partly altered to calc-silicate hornfels. ORIGIN AND AGE Schistose rocks of each widely separated exposure may be correlative because of distinctive lithologic and mineralogic similarities; if so, may be remnants of once enormously thick, widespread accumulation of mostly elastic sedimentary and mafic to intermediate volcanic rocks deposited in presumably marine eugeo- synclinal basin. Calcitic marble recrystallized from limestone; quartzite metamorphosed from quartzose sandstone or possibly chert; gray schist from clay shale, siltstone, shaly sandstone or graywacke; green schist from mafic tufl'aceous shale, m-afic tuff, or sediments derived from basaltic rocks; actinolite-chlorite schist possibly from mafic volcanic rocks or spilite (Muehlberger and Hill, 1958, p. 640); amphibole schist and talc schist from small mafic intrusions (Simpson, 1934, p. 380; Hulin, 1925, p. 26—27). Complete recrystallization of entire sequence into schist indicates regional metamorphism under condi- tions of moderately high temperature and pressure. Schistose rocks not younger than Late Jurassic or Cretaceous, inasmuch as this is age of quartz mon- zonite that intrudes them; may be Mesozoic, Paleozoic, or Precambrian. Generally believed to be Precam- brian (Hershey, 1902a, p. 273; Hulin, 1925, p. 29—30; Simpson, 1934, p. 380~381; Clements, 1937, p. 231; Wallace, 1949, p. 787). Age most likely Precambrian because of following evidence in Mojave Desert region: (1) schistose rocks generally in greater degree of regional metamorphism than any formations of known Paleozic or Mesozoic age as pointed out by Hulin (1925, p. 29—30) ; (2) no similar schistose rocks present in any formations of known Paleozoic or Mesozoic age 239—655 0437—2 other than as de-trital fragments; and (3) in Mesquite Canyon of El Paso Mountains, only place where schistose rocks and formation of Paleozoic age are in contact, Mesquite Schist unconformably overlain by comparatively less regionally metamorphosed sedimen— tary rocks of Garlock Formation of probable late Paleozoic age. MYLONITIC‘ ROCKS Zone of mylonitic rocks exposed in eastern San Gabriel Mountains southwest of Punchbowl fault in concordant relationship with Pelona Schist below and gneissic rocks above in large anticlinal arch (pl. 1) ; in Lytle Canyon area mylonite zone and adjacent schist- ose and gneissic rocks intruded by quartz monzonite; elsewhere by several thin sills and dikes of quartz monzonite aplite. Zone of mylonitic rocks as thick as 1,500 feet in western exposures; sout‘heastward thins to about 250 feet near Mount San Antonio, then thickens to about 1,000 feet in Lytle Canyon. In most places mylonite grades downward into Pelona Schist, and upward into gneissic rocks. Foliation of mylonitic rocks gen- erally parallels that of Pelona Schist and gneissic rocks. Lithology of mylonite in San Gabriel Mountains generally conforms to the following genetic description by Waters and Campbell (1935, p. 474) : First, a mylonite is a microbreccia produced by the milling down of the original rock material into an aphanitic paste which can be resolved only by the microscope; second, the rock must possess a flow structure, or lamination, as a result of the streak— ing out of the pulverized paste; third, the pulverization must have occurred under such conditions that the rock retains its coherence; and fourth, the rock must be characterized by cata- clastic rather than crystalloblastic textures. Predominant mylonite of this zone dark gray to black, hard, aphanitic; contains scattered rolled augen- like grains of plagioclase (albite or oligocl-ase) and quartz and uncommon to frequent white laminae of milled feldspar and quartz; dark aphanitic matrix presumably milled chloritic and biotitic flaky material and iron oxides. Subordinate mylonite, intercalated as layers, gray to tan, siliceous, presumably composed mainly of milled quartz and feldspar. Mylonitic rocks presumably derived from shearing and milling of gneiss and schist under great pressure at depth, probably during Mesozoic Era or earlier. Mylonitic rocks older than aplite of Late Jurassic and Cretaceous ages that intrudes them. Zone of mylonitic rocks interpreted by Noble (1954b, p. 42—43, pl. 5) and Ehlig (1959) as being along a thrust fault which they called Vincent thrust, on which gneissic rocks overrode Pelona Schist. 10 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA GNEISSIC ROCKS The gneissic rocks are described below under their local names after a general description of their lithology. Composition of gneissic rocks mainly that of quartz diorite. Banded or laminated gneiss alternates with or grades into gneissoid quartz diorite. Gneissic rocks are light to dark gray, fine to coarse grained, but mostly medium grained; composed largely of quartz, plagioclase (mainly andesine, some oligoclase), biotite, and hornblende in different proportions, small amounts of orthoclase feldspar present in some gneissic rocks either as small grains or as porphyroblasts; accessory minerals in very minor amounts are zircon, sphene, apatite, and iron oxides; some gneiss contains small amounts of chlorite, garnet, diopside, actinolite, and calcite. Gneiss composed of light-gray to White laminae from one to several millimeters thick rich in quartz and feldspar that alternate with gray laminae composed of all or most essential minerals, and dark-gray to black laminae rich in biotite and (or) hornblende. Most laminae medium grained, but some fine and others coarse grained. Biotite flakes and hornblende anhedrae oriented generally parallel to laminae. Lam- inae commonly lenticular and undulating within small area, in places crenulated, but within large area gen- erally regular. Gneissoid quartz diorite homogeneous, lithological— ly and mineralogically Similar to massive quartz diorite into which it grades; many biotite flakes and horn- blende anhedrae oriented parallel to each other give rock crude gneissoid texture parallel to the laminae of intercalated gneisses. Streaks of migmatite common in gneissic rocks, as well as lenses or zones of dark mylonite with rolled grains of feldspar and quartz. \\J \ \ v1 \ / “r. _ \\/\\/l>\/\\/\>’|/ .' \’\'/ (I/ /1\\/\‘\:’\ [a \\l \I :w / C u o —/\ \ /. /‘\ / FIGURE 3.—Geologic map of central FEE-TERTIARY CRYSTALLINE ROCKS 11 17 20 <~ PO") 7° CA/vr/L 29 // 5 l \ A . fiLfifi‘STO/R [\‘//\ MINE \\'/\\,\l7 /\’>£\ . \/‘ / /\l/ \\\\\ 2\‘ \\\\ \ "'\\\ \\\\\\\ \ \ \ .63, / i 115 \~‘: ”If " I EIO‘ 4, , I EXPLANATION Alluvium Older alluvium and fanglomerate : \\\ 2‘on Bedrock Spring(?) Formation Rhyolitic Rhyolitic Silica breccia felsite vein \25 \\310§\\\:'\\\\ \\\ ._ \\\\ ’X X Mine and prospect (gold and silver) X m Prospect (manganese oxides) and eastern Rand Mountains. X r Prospect (rhodonite) X 5 Prospect (scheelite) e , E _l Felsibe dikes Diabase dike |\/\\,/\ \/\ — 0 V2 1 MILE I\\/>\\\ \ Quartz monzonite / . I I I Gneiss Marble Rand Schist Schist Quartz veins \( I!" Ill 1 Gneiss (of Hulin, 1925) \ z z I I Johannesburg { Limestone OUATERNARY TERTIARY MESOZOIC PRE- CAMBRIAN (7) 12 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 4000 000 SEA [[VEL Bl «a \ , , // /////// //;///////// ///////// /// j N ,1/ /////// 4 w > m 4 < m m Locations of sections are shown on figure 3. 2 FIGURE 4.—~Secti0ns of Rand Mountains. SEA LEVEL / 7 / é/ /é / {Y 4000’ o o o N SEA LEVEL FEE-TERTIARY CRYSTALLINE ROCKS 13 In some places gneissic rocks contain lenses of bio- tite schist, marble, and few of quartzite, all parallel to foliation of enclosing rocks; schist highly foliated; marble and quartzite foliated or lineated locally. Most marble lenses not more than 50 feet thick or half a mile long, few thicker and longer; marble white, mas- sive, medium to coarsely crystalline, dolomitic Ito rarely calcitic, commonly contains silicates such as muscovite flakes, forsterite, diopside, and (or) antigorite; some layers contain graphite. Quartzite forms thin lenses, is light gray, massive to thin layered, vitreous, com- posed mainly of quartz, flakes of mica, and grains of feldspar. UNNAMED GNEISSIC ROCKS Gneissz'c roe/cs of San Gabriel Mountains and west— ern San Bernardino Mountains—In San Gabriel Mountains southwest of Punchbowl fault, sequence of gneissic rocks as thick as 10,000 feet overlies mylonitic rocks; foliation dips southwest (pl. 1). Lower part of sequence predominantly gneiss; basal part transi- tional through cataclastic and mylonitic gneisses into underlying mylonitic rocks; upper part mainly gneis- soid quartz diorite containing zones of migmatite; no marble or quartzite; in places gneiss intruded by thin sills and dikes of aplite. Rocks exposed on Pinyon Ridge and ridge west of Valyermo between Punchbowl and San Andre-as faults mapped by Noble (1954a) as “Pinyon Ridge granodio- rite,” but are composed of gneiss as well as gneissoid granodiorite and quartz diorite and therefore mapped herein as gneissic rocks; foliation trends nearly east- west, nearly vertical (figs. 29 and 30); total exposed thickness of gneissic rocks as indicated by foliation attitudes about 6,000 feet; contains no marble nor quartzite. Foliation of gneissic rocks exposed northeast of San Andreas fault along northeast margin of San Gabriel Mountains and western San Bernardino Mountains strikes east to southeast, dips north; about 9,000 feet of foliated sequence exposed; mainly gneiss, some gneis- soid quartz diorite; contains lenses of dolomitic mar- ble as much as 300 feet thick, traceable 4 miles (pl. 1) ; to northeast, gneissic rocks apparently grade through gneissoid quartz diorite and granodiorite into quartz monzonite. Gneissz'c rocks near Sierra Pelona.—Gneissic rocks exposed between Sierra Pelona and San Andreas fault to the north. Complex consists of gneiss and gneissoid granitic rocks composed mainly of granodiorite, but ranging from diorite to quartz monzonite. Foliation strikes north of east, dips steeply north to vertical. About 20,000 feet of thickness exposed if homoclinal. Several lenses of marble in northern part of outcrop area; some white aplitic dikes and sills. In general, rocks grade northward from granodiorite into quartz mon- zonite. Gneissz'c rocks of Frazier Mountain—Rocks crop out on Frazier Mountain southwest of San Andreas fault; consist of exposed complex of gneisses and some quartz diorites intruded by aplitic dikes and sills. Some bio- tite gneiss with ‘porphyroblasts or augen of potassium feldspar. Foliation of gneissic rocks much contorted but trends generally northwest, dips steeply northeast. Gneissz'c rocks in mountains north of Garlock fault zone.—Gneissic rocks associated with massive to gneis- soid quartz diorite exposed in Tehachapi Mountains mainly in upper El Paso Creek, described by Wiese (1950, pl. 1, 15). Also occur at southeast margin of southern Sierra Nevada Where gneissic rocks contain lenses of marble. In western El Paso Mountains quartz diorite contains lenticular inclusions of biotite- rich gneiss. Gneisstc rocks in western Mojave Desert.~—Gneissic rocks exposed 2 miles north of Johannesburg, described and mapped as Johannesburg Gneiss by Hulin (1925, p. 21—23, pl. 1), apparently overlie his Rand Schist, dip steeply north. About 2,800 feet exposed (figs. 3, 4) ; some layers rich in hornblende; several layers of marble, a few of impure quartzite, all parallel to foliation of gneiss. At Catholic Hill 4 miles east of Victorville, pendant in quartz monzonite contains nearly 1,000 feet of gneiss and intercalated quartzite; another pendant 6 miles northeast of Castle Butte contains about 500 feet of gneiss and quartzite; very small pendant of gneiss exposed a mile north of Boron. Near Oro Grande, granite gneiss is yellowish gray, nonlaminated but foliated, fine grained; composed es- sentially of quartz, microcline, and plagioclase (albite- oligoclase) with slight predominance of microcline, and small percentage of biotite as small parallel flakes forming foliation of rock; feldspar occurs also as scattered grains about three times larger than average grain size of rock. Figure 14 shows structure, thick- ness, and relation to adjacent rocks. Gneiss in hills 6 miles south of Barstow similar but contain dark laminae rich in biotite, generally undulating, in places crenulated; injected by quartz monzonite. wumuun GNEISS Waterman Gneiss of Barstow, Hinkley, and Harper Valley areas.—Gneiss and quartz diorite containing intercalated marble and quartzite exposed in hills north of Barstow, hills near Hinkley, and hills west 14 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA and northwest of Harper Valley. Miller (1944, pl. 6, p. 77—98) called gneissic rocks containing abundant intercalations of marble Hinkley Valley Complex, and those containing little or none, Hodge Complex. Bowen (1954, pl. 1, p. 17—22, 53—54) named gneissic rocks exposed in hills 2-4 miles north of Barstow Waterman Gneiss (type locality) ; those in hills north- west of Barstow he designated as gneissic hornblende diorite, and those containing abundant intercalations of marble and some quartzite exposed farther north- west in these hills, and in the vicinity of Hinkley, he referred to Oro Grande Series. In this report all these gneissic rocks are included in Waterman Gneiss because all are phySlcally and lithologically similar, appear to be regionally metamorphosed to same extent, and are physically unlike Oro Grande Formation. Planar foliation in Waterman Gneiss generally con- spicuous and parallel to lenses of marble and quartz- ite, but in many places obscured by lineations of vari- ous attitudes and by minor crenulations formed by plastic flow formed during metamorphism, as shown by Wiese (1954). In hills 2—4 miles north of Barstow attitudes of discernible planar foliation indicate sev- eral folds having axes trending northeast (figs. 5 and 6), which apparently expose possibly 4,000 feet of gneissic rocks containing intercalations of marble as thick as 50 feet; some partly containing specular hema- tite. Lirthology and planar structure of Waterman Gneiss in hills 1—6 miles northWest of Barstow nearly similar except part contains more intercalations of marble and some of quartzite (fig. 5), possibly about 5,000 feet of gneissic rocks exposed. In both areas, gneiss grades through gneissoid quartz diorite into granodiorite or quartz monzonite to northwest. In Iron Mountain area southwest of Hinkley, about 8,000 feet of nearly vertical Waterman Gneiss ex- posed; includes layers of marble as thick as 300 feet (figs. 7, 8). Gneiss grades into gneissoid quartz dio- rite to northwest. In low hills northwest of Hinkley, pendants of gneissic rocks contain several layers of quartzite (fig. 9); other pendants west of Harper Valley contain many layers of dolomitic marble (fig. 10) that locally contain forsterite (partly altered to antigorite), diopside, magnesium spine], and other magnesium silicate minerals. omem AND AGE Gneissic rocks recrystallized at moderate to great depth under conditions of high temperature; possibly partly melted in place or partly magmatic in origin. Gneiss probably recrystallized from sedimentary rocks as indicated by intercalations of marble, quartzite, and biotite schist; possibly in part crystallized from mag— mas or solutions injected along foliation planes. Gneissic rocks intruded by plutonic rocks of Late Jurassic or Cretaceous age, therefore older. In west- ern San Gabriel Mountains, gneiss intruded by gabbro— norite and anorthosite dated by lead: alpha measure- ments on zircon as 930190 and 810:80 million years, or Precambrian (Neuerburg and Gottfried, 1954, p. 465; Oakeshott, 1958, p. 24, 48). In Bear Valley area of San Bernardino Mountains, gneiss overlain with angular unconformity by Paleozoic sedimentary rocks. Therefore most if not all gneiss and included meta- morphic rocks in western Mojave Desert probably Precambrian. However, gneissoid quartz diorites and migmatic gneisses may be younger,'possibly Mesozoic. Age relation of gneissic rocks to schistose rocks is con- troversial and requires further study. METASEDIMENTARY ROCKS Remnants of a once-extensive and thick sequence or sequences of metasedimentary rocks of marine origin are exposed as isolated pendants in the batholithic masses of Mesozoic granitic rocks of the Mojave Desert, mostly in the southeastern part of the area and in the mountains along the northwestern border. The metasedimentary rocks are generally similar in their lithologic character, and in their relatively low grade stage of regional metamorphism as compared to that of the older dyn-amothermal metamorphic rocks. However, the stratigraphic sequence of each pendant is different, and with few exceptions, unfossiliferous, so that definite correlations and precise reconstruction of stratigraphy are not possible. The few fossils found in some pendants are all marine types known from rocks of late Paleozoic age. Consequently the metasedimentary rocks are presumed to be of that age, although some may be as old as Precambrian and some as young as Mesozoic. - Five local formational units are shown on plate 1, but because of their isolated positions and the scarcity of fossils, their ages and stratigraphic order are not ' completely known. The units are: unnamed metasedi- mentary rocks, Bean Canyon Formation, Oro Grande Formation, Fairview Valley Formation, and Garlock Formation. UNNAMED METASEDIMENTARY ROCKS Metasedimentary rocks of El Paso Mountains.— Rocks occur as a thin pendant across western El Paso Mountains, 1 mile east of Bedrock Canyon (fig. 63, pl. 1). Consist of quartzite, metaconglomerate, and hornfelsic rocks. Conglomerate predominates in lower (western) part, hornfelsic rocks elsewhere. Metacon- glomerate composed of originally rounded pebbles as much as 2 inches long in somewhat schistose dark-gray matrix of impure micaceous quartzite; pebbles flattened FEE-TERTIARY CRYSTALLINE ROCKS 15 US HWY 466 KEEN 32 4 r CHISOM rOp E434 _,\‘ 4’) Z FIGURE 5.—Geolog1'c map of hills north of Barsrtow. See figure 6 for explanation and sections. 16 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA SEA LEVEL A NW A’ ,_ \‘\ \‘ \ \/ \ \-—"-— .1 [V/— i I 1/ ~-/ 2000 5/ l \> A \L A4 \ v <\\“\\\\\\ \\‘\‘\’\\§{\_\(\l>/\,\:\ ~'~';\JL\$§:7§I:ZJ:\' ,r‘ - ,3- ». — / \ , I ‘ ‘ \\ _~\— \ ’_{\r:v‘7/ ‘k\ I: uni/I 7’ / \ SEA LEVEL SW 3' ,n=o’4*¢‘+n+ 4\/l\l\ E >‘ all an A++ 4 fl/ 1\-\ -2000' '— \ " A4 1' + A / \ \ L \ §U + + A + q ‘ \ \ / 0 4 + l H __ V \g P + + 4, / P m \ + A A \ ’ v =- + + 4 «LINN/l ,\ a » \T§A++ ++\A \\ >\ SEA ‘ LEVEL LEVEL o 9% 1 MILE EXPLANATION “ >- § D m d“: < Surficial sediments E Lu “a i- -§§ 3 E 3 o Miocenefl?) E: . B l a . § , '. m L FIGURE 6.—Sections of hills north of Bax-stow. Older alluvium E, :4 § / J" Intrusive dacite o o.o Conglomerate 42 Felsite and quartz latite porphyry Quartz monzonite and aplite \\ z/ \\ //, \ |\ /// Gneiss i Tuff J, A‘q+ A‘+¢1+‘1 Tuff breccia MESOZOIC E Marblé @ Rhyolite breccia ~V< r) v—‘r «A Granodiorite ( / q 4/ /L 1 / \l Quartz diorite Pic khandle Formation Homblende diorite and gabbro 5 0) {£5 Quartzibe B TERTIARY Y MESOZOIC OR OLDER PRECAMBRIANH) Locations of sections are shown on figure 5. FEE-TERTIARY CRYSTALLINE ROCKS R.4W. R.3W. Us HIGHWAY 1466 A Aa\ 4"? as 64 V V" 36 31 l \ 32 “RA “7‘35 > ,1 k ‘ \ ' \ IKM \ 87' \ ~ \ \ l \‘ \\ \ 4 I \ % x N ,2 \x I' r x T \ I \ \L w 9 \lg‘I/ll ‘“ ‘ \ I I\ l N “NIH/In 5| 7! /////IJ\ I, —1 4 //{‘/’/13/ ' 2 * b ‘ é /’ 1 4 /l/ l/\ 5 7 / 7 L/ ,1 1, , / A /I/ / /// ,’ _, // ,’ ,; ' ’.—/I 4, , , // 5/5), HINKLEV l b // /I,I DOLOMITE r / / QUARRY // / // / Iron Mountain (1’ == § ‘ \\26H // 5: / \\u \\/,,\\\\// /\ \\‘_,_——-——\_ zmazma H 1 MILE FIGURE 7.—Pre~Tertia1-y geology of Iron Mountain area. See figure 8 for explanation and sections. 18 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 2000’ - SEA LEVEL SEA LEVEL /\ ‘1"); {113/}: SEA LEVEL E Alluvial sediments E- Qumz latite Aplibe and felsiee / \ \ ’ / I, //, Quartzmonzonite 4 > < V A T Quartz dioribe \\ S I/ \ \\ Homblende diorite-gabbm \Ql 176$, 0 ’ , o Granodiorite porphyry FIGURE 8.—Sections of Iron Mountain area. Locations of sections are shown on figure 7. MESOZOICVOR OLDER OUATERNARY 36 1 MILE L._.—L_____J EXPLANATION ‘ Quartzibe Sericite - Schistose muscovice metaquartz schist latite 42$ 6 U 9 0 Quartz latite dacite porphyry J ‘ = Quartzite v Waterman Gneiss Hodge Volcanic Formatxon v PERMIAN AND MESOZOIC PRECAMBRIANU) , SEA LEVEL PRES-TERTIARY CRYSTALLINE ROCKS l9 SEA LEVEL 22 o o Hinkley Q % SEA LEVEL EXPLANATION }E >- |_ n: < < Alluvium and older alluvium a Z / \ // »/ 0 cc 6 m Quartz monzonite N a 0 o \\ ” \\ ’/ S n: o \\ fl 2 o g; Quartz diorite ‘3 5 _ Z = m u] 5 a — n: g E Quartzite Marble Tactite '1 2 < S 0 FIGURE 9.—Geologic map and sections of hills north of Hinkley. parallel to schistosity of matrix; most pebbles of gray- White quartz, few of tan to brown felsites. Hornfelsic rocks massive to indistinctly bedded, compact, micro- crystalline; composed of dark-greenish-brown nodular calc—silicate rocks and dark-brownish-gray to nearly black metamorphosed andesite or basalt. F ine-grain size and inferred mineralogy suggest low- grade regional metamorphism; age uncertain but on plate 1 assigned to Paleozoic for simplicity. Metasedz'mentary rocks of southern Sierra Nevada. and northern .Tehacluzpi Mowntaz'ns.—Biotite schist and marble, in part migmatized, presumably of Pale- ozoic age; occur as small isolated pendants in 'plutonic rocks of mountains west of Sierra Nevada fault and northwest of Garlock fault (pl. 1). Metasedimentarg/ rocks of southwestern Tehachanpi Mountains.—Pendants of white to light-gray marble, some hornfels, schist, quartzite, and tactite; occur in granite in southwestern Tehachapi Mountains south- east of Garlock fault (fig. 11). Described and mapped as Paleozoic( ?) rocks by Wiese (1950, pl. 1, p. 16—19) and metamorphosed Paleozoic( ?) sedimentary rocks by Crowell (1952, pl. 1, p. 6). Rocks similar to Bean Canyon Formation to northeast. BEAN CANYON FORMATION Pendants of metasedimentary rocks exposed in east— ern Tehachapi Mountains southeast of Garlock fault mapped as Bean Canyon Formation (figs. 12, 13) originally named Bean Canyon Series by Simpson (1934, p. 381—383, pl. 5). Pendant in Bean Canyon designated type section (fig. 13). Rocks composed of nearly two-thirds meta—argillite or fine-grained dark schist, about one—third carbonate rocks, and minor amounts of quartzite and metabasalt. Metabasalt (only in Bean Canyon pendant, fig. 13) is black, locally amygdaloidal, fine grained; composed of dark plagioclase and ferromagnesian minerals largely altered to antigorilte, chlorite, and iron oxide. Rocks unfossiliferous, therefore of doubtful age. General lithologic similarity to known Paleozoic meta— sedimentary rocks and apparent similarity in stage of regional metamorphism suggest formation most likely Paleozoic in age. 0R0 GRANDE FORMATION 0ro Grandd?) Formation of 0ro Grande-Victor- ville area.~—Sequence of carbonate rocks, calc-silicate hornfels, schist, and quartzite east of Oro Grande and Victorville (pl. 1) originally described as Oro Grande 2O Q AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA EXPLANATION E Alluvium - Older alluvium \/\ //\ Quartz monzonibe ////\ \\\\//// Gneissoid quartz Homblende diorite E diorite 8 U s @ E Quartz diorite White marble 3' gneiss a B Quartz latibe pox-phyry dikes 14 } NARY MESOZOIC MESOZOIC OUATER- OR OR OLDER TERTlARY E__Y_ PRE< CAMBRIAN ('2) SEA LEVEL SEA LEVEL FIGURE 10.—Geologic map and sections- of hills west of Harper Valley. SEA LEVEL PRE-TERTIARY CRYSTALLINE ROCKS 21 SEA LEVEL 2000’ SEA LEVEL EXPLANATION Recent r—L.‘ >. _ fl: Alluvmm é UNCONF’ORMITV at Ll] l.— l c < ‘5 ' D g g o o o m 3 Older alluvium , > r UNCONFORMITY : I > I Q \ v > a w 5 . , .. l n: \ S: u. - . ‘ . g :5 L:: ,1: § § :5 Sandstone and r n: 3 gm conglomerate . E 1 JNCONFORMITY ’ \/,/ \1 l\ ’ Granite >. II E '— . K Quartz dionte E u'J II Limestone and Schist and marble homfels FIGURE 11.——Geologic map and sections of Bronco and Antelope Canyon area, Tehachapi Mountains (modified after Wiese. 1950) . 22 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA I +‘-_++ I\\ \/I +' 2 /\\ ‘M x x - l’c’z’ / EXPLANATION C] Alluvium ”on n ‘ Clay and sand Gravel and sand Older alluvium Quartz lati’oe felsite dikes SEA LEVEL SEA LEVEL MESOZOIC MESO- TERTIARY QUATERNARY 9 8 Granite - (I A DJ Quartz monzonite Quartz diorite a O n: O Homblende dioribe IE Schist Marble Bean Canyon Formation PALEOZOICC’) FIGURE 12.—Geologic map and sections of Tehachapi Mountain foothills in vicinity of Tylerhorse Canyon. FEE-TERTIARY CRYSTALLINE ROCKS 23 Series by Hershey (1902a, p. 27 8—288), later by Baker (1911, p. 334—335) and Darton and others (1915, p. 163). Described and mapped by Miller (1944, p. 98) and Bowen (1954, pls. 1, 6, p. 23-26). Outcrop at Quartzite Mountain near Oro Grande designated as the type section by Bowen (1954, p. 24—25) . Oro Grande Formation characterized by lenticular- i=ty of units (figs. 14, 15) ; sequence at Quartzite Moun— tain as given below in descending order (northeast to southwest). Oro Grande Formation of Quartzite Mountain area (secs. 9, 10, 11, 14, 15, 16‘, 17, T. 6‘ N., R. 4. W., fig. 14) Metamorphosed felsite agglomerate. fifgfifi? Unconformity (‘1’). (feet) Schist, dark-gray, very fine grained _____________ 0—100 Limestone marble, blue-gray, bedded, finely crys- talline _____________________________________ 250—400 Schist, dark-gray, thin-bedded, very fine grained, micaceous; thins eastward ___________________ 0—500 Limestone marble, blue-gray, bedded, finely crys- talline; thins eastward _______________________ 0—800 Quartzite, pinkish-tan, massive, fine-grained; con- tains intercalated limestone in sec. 11 _________ 0—200 Schist, black, thin-bedded, very fine grained mi- caceous; includes a few thin beds of limestone marble; thickens eastward ____________________ 200—700 Dolomite marble, white, thick-bedded, fine to coarsely crystalline __________________________ 1, 000—1, 200 Schist, dark-gray, fine-grained, micaceous ________ 0—200 Limestone marble, blue-gray, bedded, finely crys- talline ______________________________________ 100—250 Schist, dark-gray, fine-grained, micaceous ________ 100—350 Quartzite, pinkish-tan, massive, fine-grained; forms ridge of QuartziteaPeak ______________________ 150—300 Hornfels, pinkish— to greenish-gray, bedded, very fine grained calc-silicate layers; thins eastward- . 0—150 Schist, gray-black, thin-bedded, very fine grained, micaceous; contains a few thin interbeds of blue- gray limestone marble; thins or grades laterally westward into overlying hornfels ______________ 300—650 Schist, like that above; contains several lenses as much as 300 ft thick of blue-gray limestone and dolomite marble and two lenses as much as 150 ft thick of tan quartzite __________________ 1, 000—1, 600 Total approximate thickness of Oro Grande Formation ___________________________ 7, 400 Granite gneiss. In hills 2—4 miles northeast of Victorville is a 3-mi1e- long pendant of Oro Grande in Iplutonic rocks. North- ern part marble, about 500 feet thick; southern part black fine-grained schist containing lenses of white marble and one of quartzite, flanked on east by meta- morphosed quartz latite( 2). 07-0 Grande (.9) Formation of Shadow Mountains.— Metasedimentary rocks preserved as large pendant in northern part (Troxel, 1954) and another in southern part of Shadow Mountains questionably referred to Oro Grande Formation (figs. 16, 17). Both pendants partial sequences, complexly deformed; neither base nor top preserved. Thicknesses of lithologic units within each pendant differ greatly, perhaps because of plastic flow during deformation. accompanying meta- morphism. 0ro Grande(?) Formation exposed on southeast flank of anticline in northern Shadow Mountains (secs. 99, 31, 32, 33, 34, T. 8 N., R. 6' W., fig. 16', east to west) Top of section concealed by alluvium, and intruded by 15%,?"sz quartz monzonite to west. (feet) Marble, white to gray-white ______________________ 200 Schist _________________________________________ 1, 600 Dolomite marble, white; lenses out(?) to west ______ 0—150 Schist; lenses out to west, then reappears __________ 0—150 Dolomite marble, white; lenses out to west, then re- appears west of fault as a thin layer _____________ 0—400 Dolomite marble, white; thins westward; forms crest of mountains _________________________________ 100—600 Quartzite; lenses out to west and east _____________ 0—30 Hornfels _______________________________________ 300 Schist _________________________________________ 700 Quartzite; lenses out to west and east _____________ 0—50 Hornfels and schist; contain several thin layers of marble ______________________________________ 800+ Granitic intrusions on axis of overturned anticline. —— Total thickness exposed ___________________ 4, 980+ Oro Grande(?) Formation exposed in southeastern Shadow Moun- tains (secs. 30,31, T. 7 N., R. 5 W., sees. 25, 96', 27, 34, 35, 36’, T. 7 N., R. 6‘ W., fig. 17, west to east) Thrust fault at top of section. fifgkmnflff Hornfels; contains some intercalated schist and a few (feet) thin layers of light-gray limestone marble __________ 800 Limestone marble, blue-gray; contains about 50 ft of schist near base that wedges out northward ________ 1, 200 Schist ___________________________________________ 300 Limestone marble, blue-gray _______________________ 200 Hornfels; contains some intercalated schist and thin layers of limestone marble, a few of quartzite; lower part concealed by alluvium ______________________ 600 Concealed by alluvium, but iso‘ated exposures of light blue-gray limestone marble in sec. 30, T. 7 N., R. 6 W_ 150+ Hornfels, synclinally folded; top concealed by alluvium- 200+ Schist ___________________________________________ 150 Limestone marble, gray-white ______________________ 500 Schist ___________________________________________ 250 Limestone marble, gray-white ______________________ 500 Schist; wedges out northward ______________________ 250 Marble, white; base concealed by alluvium ___________ 400 Total thickness exposed _____________________ 5, 500 + 24 .23.“! AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA EXPLANATION l: >. [I Alluvium g Calllomia 0: Portland u] Cement Co ’ 2 ° mill 3 . O /} Older allnvmm o/ >. / n: S ’— Rhyolitic felsite E |~ + + 4. + + in H" n: . LU Granite D .J O | / \" (I - / O . U Quartz monzombe 6 N O U) m ‘ 2 Homblende diorite E 5 W F3 1 W 9 .5. __ O a _ N E . . o {2 Marble Schlst Quanzxte Metabasalt a < D. N l .l i 1 MILE l B B’ 4000' 4000' 4000' 2000' 2000' 2000' / r _ ’ \ I /\I l/\ \_\— g ;\\E//\‘\ SEA /‘ fl : //_‘\'/’\/\l/\/T/:‘\,\\ _‘/\,/71\‘l‘7\‘,/x SEA LEVEL LEVEL SEA LEVEL FIGURE 13.—Geologic map and sections of Tehachapi Mountain foothills between Bean Canyon and Oak Canyon. PRE-TERTIARY CRYSTALLINE ROCKS 25 OM Grande Formiztion exposed in central southern part of Shadow Mountains (secs. 27, 28, 33, 34, T. 7 N., R. 6' W., fig. 17, east to west) Esti- mated . thickness Thrust fault at top of section. (feet) Schist _____________________________________________ 1, 800 Hornfels ; contains intercalated schist and a few thin lenses of limestone marble _______________________________ Schist; includes some intercalated hornfels and lenses of light blue-gray marble as much as 200 ft thick; anti- clinally folded and intruded from below by quartz mon- zonite ___________________________________________ l, 500 1, 200 Total thickness exposed ________________________ 4, 500 Oro Grande Formation exposed in southwestern Shadow Mountains (sec. 82, T. 7 N., R. 6 W., secs. 4, 5, 8, 9, 16, T. 6 N., R. 6 W., fig. 17, northwest to southeast) Esti- mated thickness (feet) Intrusive quartz monzonite. Schist; includes a few thin layers of marble and calc—sili— cate hornfels ___________________________________ l, 500 Marble, white, fine-crystalline ______________________ 500 Schist ___________________________________________ 400 Limestone marble, blue-gray _______________________ 500 Schist___________-_________-_____' ________________ 200 Limestone marble, blue-gray; in part intertongues ' northwestward into schist; basal part concealed by alluvium _______________________________________ 1, 200 Schist; contains some intercalated hornfels and mar- ble exposed only in an isolated hill (in sec. 8) sur— rounded by alluvium ____________________________ 300:}: Total thickness exposed _____________________ 4, 600:1: Ora Grande(?) Formation of Sidewinder Mountain area—In east-trending ridge at north end of Side- winder Mountain, 15 miles east of Oro Grande, rem- nants of metasedimentary rocks referred to Oro Grande Formation by Bowen (1954, p. 27—31, pl. 1). Occurs here as two large pendants (fig. 18). Another ex— posure in Black Mountain west of Sidewinder Moun— tain (fig. 20). Small pendants in Granite Mountains. One large pendant in Sidewinder Mountain com- posed of dark biotite schist, dolomite marble, and thin layers of quartzite. Another consists of black mica- ceous schist and white dolomite marble. In Black Mountain mainly gray-white limestone marble con- taining thin intercalations of hornfelsic calc-silicate rock; uppermost part altered to massive tactite (Bow— en, 1954, p. 33, 34). Small pendants in Granite Moun- tain, marble, biotite schist, and quartzite; in places marble silicated to tactite or metasomatized to horn- blende diorite or gabbro. Oro Grandd?) Formation of Juniper F tat area.— 239—655 0—67—3 In Juniper Fla/t area of northwestern San Bernardino Mountains gray-white dolomitic marble and black fine- grained biotite schist, similar to Oro Grande Forma- tion, prominently exposed as pendants in plutonic rocks (fig. 19). Crinoid stems suggesting Carboniferous age re- ported from west slope of Juniper Flat by Noble (1932). FAIRVIEW VALLEY FORMATION Fairview Valley Formation of Black Mowntain area. —Sequence of hornfels, limestone, and conglomerate exposed in Black Mountain and hills to west about 15 miles east of Oro Grande (fig. 20) described, mapped, and named Fairview Valley Formation by Bowen (1954, p. 36—42, pl. 1), and officially adopted for use in this report. Probably unconformable on marble of Oro Grande Formation, if not in fault contact. Lower unit of formation composed mainly of dark- greenish- to brownish—gray, laminated thin-bedded platy hornfels; contains several units as much as 300 feet thick of dark-greenish-brown ferruginous lime- stone and interstratified platy hornfels; individual limestone beds not more than 5 feet thick; several layers 1—25 feet thick of pebble conglomerate com- posed of scattered to abundant subrounded pebbles of porphyritic andesitic rocks, granitic rocks, quartzite, hornfels, and limestone in ‘matrix of sandy or gritty hornfels or gray arkosic metasandstone. Upper unit composed of limestone cobble conglom- erate containing poorly sorted rounded clasts as much as 2 feet in diameter of dark-blue—gray to black lime- stone in matrix of dark-gray fragmental limestone; few clasts of brown quartzite and chert. Fairview Valley/(.9) Formation in Sidewinder M oun- tain.—Dolomitic breccia or conglomerate at Three Color Marble quarry on north side of Sidewinder Mountain (fig. 18) described by Pack (1914a, p. 363—368) and Bowen (1954, p. 30, 146—147, figs, 7, 8, 68.). Referred to Fairview Valley Formation. About 200 feet thick. Composed of well—sorted subrounded to angular peb- bles and cobbles of white dolomite in greenish-gray to greenish-black, partly silicated, dolomitic marble; no fossils found. Unconformable on white marble of Oro Grande( ?) Formation. Fairview Valley(?) Formation near Spark/Lute Mountain—«About 200 feet of limestone conglomerate exposed just north of Sparkhule Mountain (fig. 14); composed of flattened cobbles and pebbles of black limestone in dark-gray limestone matrix; rock weathers light brown. 26 . AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA _ \ , "\Il;/ L-";\’I~ \’ ‘ \ ‘ I \ \K‘x7)—:/\\_. l/L EXPLANATION SEDIMENTS E W > E < Alluvium Z ,0: - E < ‘7 a v D O Fanglomerate 4 UNCONFORMITY PLUTONIC ROCKS n: 9 Lu 0 0 >3 "‘ o w 1 MILE m 0 N I 2 O Quartz diorite , HYPABYSSAL AND METAVOLCANIC ROCKS [1 PATLX': METASEDIMENTARY ROCKS ; (—41!“ g SE 3 ‘ Felsite ; ESE g 92 I: g I: Limestone conglomerate a g g g; E 3 fl *3 < EE 5 a: U I: Quartzite Schist Hornfels Limestone Dolomite & E g GNEISSIC ROCKS 3 «3 & < Z I) u': E n: n: D. m E Felsite agglomerace 0 FIGURE 14.—-Geologic map of Quartzite Mountain area. Garlook Formation of El Paso Mountains.—Garlock Formation originally described and mapped as Garlock Series (Dibblee, 1952, p. 15—19, pl. 1) ; superbly ex- posed in central El Paso Mountains; ofiicially adopted PRE-TE RTIARY CRYSTALLINE ROCKS A A’ . Sparkhule , 4000 Mountain _ 400° __ M7— \ "- 17¢ 2000' / ‘ \ \ -2ooo' /\ ‘ \ 7111 ’~7§%1§: /\//\ 7 / \ /\// ,/\ , _ >9??— _ , {\\ \‘\/\’/\///\l,\\ ’\ / \‘/I \ "/ \ 7\ \/‘/\ ’/’\’+ SEA LEVEL SEA LEVEL Quartzite Mountain SEA LEVEL 5 n z m m FIGURE 15.—Sections of Quartzite Mountain area. GARIJOCK FORMATION for use in this report as Garlock Formation. Garlock Formation differentiated into 22 units as shown on figures 21 and 22. Lithology and strati- graphic sequence of units in descending order are shown below. Unit 22. 21. 20. 19. Garlock Formation of El Paso Mountains Tactite: stratified to massive greenish- brown fine— to medium-crystalline gar- net-epidote rock ____________________ Hornfels: stratified to massive brownish- gray finely crystalline calc-silicate rock and micaceous schist; grades southeast- ward into white marble _____________ Phyllite, stratified, dark-brownish—gray, micaceous; grades into mica-quartz schist near quartz diorite contact _____ Hornfels: thin-bedded tan to light-gray aphanitic calc-silicate rocks; interbed- ded with platy calcareous to micaceous phyllite; contains O—30-ft-thick lens of black chert in upper part; 0—30-ft— thick lens of brown quartzite in lower part ______________________________ Chert: black, thin-bedded _____________ Phyllite and hornfels: thin-bedded gray micaceous slaty phyllite; interbedded gray to pinkish-tan calc-silicate horn- fels; contain few lenses of gray marble and dark chert _____________________ Eati mated thickness (feet) 1, 200 1,000 1,000—2,000 1,200 0—200 3, 700 Unit 18. 17. 16. 15. 14. 13. Locations of sections are shown on figure 14. Phyllite, gray, thin-bedded, micaceous; contains some interbedded calc-silicate hornfels and lenses of gray marble--__ Chert, black to gray, thin-bedded; con- tains thin layers of marble ___________ Hornfels, cream-tan to greenish-gray, thin-bedded; contains some interbed- ded dark-brown slaty phyllite; 0—100 ft of dark chert and siliceous phyllite at base ____________________________ Heterogeneous rocks: interbedded dark- gray slaty phyllite, tan to light-gray calc-silicate hornfels, dark chert, and gray limestone marble containing cri- noid fragments; 0—100 ft of greenstone near middle _______________________ Total thickness unit 18 _________ Phyllite, dark-gray, thin-bedded, slaty, micaceous; weathers brown; _________ Heterogeneous rocks: interbedded dark- gray slaty phyllite, light-colored calc- silicate hornfels, dark-colored chert, and some gray marble ______________ Phyllite: similar to that of unit 17 _____ Chert and phyllite, gray to black, thin- bedded; a few lenses of chert-pebble conglomerate as much as 2 ft thick- _ _ Andesite, dark-gray, porphyritic ________ Limestone, dark-gray, massive____ _ _ _ _ _ _ Chert, black to brown-gray, and tufi‘a- ceous(?) phyllite ____________________ 27 2000’ SEA LEVEL Garlock Formation of El Paso Mountains—Continued Eatimated thickness (feet) 1, 100 0—300 700 2, 300 4, 300 :l: 1,600—2,500 900—2, 000 500-700 600—1, 300 700 50 300 28 12. 11. 10. AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Garlock Formation of El Paso Mountains—Continued Andesite: like that above; thickens southeastward; contains tongues of chert to northwest; in Iron Canyon lower 0—100 ft altered to pink-gray sheared sericitized schistose material__ Andesite, flow breccia, and tufi breccia, pink-gray to brown, somewhat schistose- Total thickness unit 13 _________ Phyllite, gray, thin-bedded, slaty; con- tains thin layers of chert and greenish- tan limestone marble containing cri- noid fragments, and of chert-pebble conglomerate and sandstone _________ Conglomerate: flattened pebbles of chert, phyllite, and quartzite, in matrix of gray schistose sandstone or graywacke- Phyllite, gray to tan, thin-bedded to fissile; contains interbeds of tan fer- ruginous limestone that thicken south- eastward; in northwestern exposures limestone strata contain crinoid frag- ments, fusulinids, and pebbles of chert and limestone ______________________ Total thickness unit 12 _________ Quartzite, tan, massive; brown quartzitic to micaceous phyllite _______________ Quartzite, tan, thick-bedded to massive, very fine grained; grades southeast- ward into quartzitic and micaceous phyllite ___________________________ Phyllite, gray to brown, thin-bedded, slaty, micaceous; contains interbeds of tan micaceous quartzite and gray chert- Chert, black, gray, brown; contains a few thin lenses of limestone marble _______ Phyllite: like that above; contains some tan siliceous (tufiaceous?) shale in south— eastern exposures; 0—200-ft—thick lens of white quartzite near base at crest of mountains _________________________ Chert, gray, brown, tan, thin-bedded--- Total thickness unit 9 __________ Greenstone: vesicular dark metabasalt; thins and pinches out southeastward- Chert, black to tan, thin-bedded; contains interbedded phyllite layers; grades northwestward into siliceous phyllite- Phyllite, gray to black, thin-bedded, slaty, micaceous, brittle, siliceous; contains some thin-bedded quartzite and chert layers _____________________________ Limestone, marble, dark-greenish—gray, thick-bedded; contains numerous quartz grains, interbedded chert and phyllite; lenses out to northwest; to southeast, marble overlies and underlies thick tongue of dark chert conglomerate like that of unit 3 ______________________ Estimated thickness (feet) 1, 100—3, 100 500 4, 950:}: 1,100 250 700 2, 0504 500 800 1, 500 500 1, 300 200—500 3, 800 :1: 0—1, 400 400—600 600—1, 000 0—600 Garlock Formation of El Paso Mountains—Continued 4. Phyllite: like that of unit 6; in southern foothills upper part includes one or more fifzflzfid massive beds as thick as 100 ft of lime- (feet) stone marble similar to that of unit 5-- 900-1, 300 3. Chert conglomerate: flat pebbles of chert, few of phyllite and limestone marble, in matrix of gray-black chert ____________ 200—300 Phyllite: like that of units 6 and 4; thickens to south where it contains 0—100-ft-thick‘ lens of chert conglomerate base _______________________________ 50-200 Total thickness unit 3 ___________ 200—500 2. Greenstone: vesicular dark metabasalt; thins southward _____________________ 200—1, 500 1. Phyllite, dark-gray, thin-bedded, cherty, siliceous to micaceous, schistose; fer— ruginous, graphitic basal part contains flat pebbles of phyllite(?) and at one place 54 mile north of Mesquite Wash contains fragments of Mesquite(?) Schist ______________________________ 200—400 Approximate exposed thickness of Garlock Formation (including intrusive? andesite) ____________ 35, 000 Angular unconformity. Mesquite Schist. AGE Metasedimentary rocks of western Mojave Desert nearly devoid of diagnostic marine fossils; meager fossil remains found only in Oro Grande, Garlock, and Fairview Valley Formations at a few places. Age of unfossiliferous unnamed metamorphic rocks in western El Paso Mountains; Precambrian, Paleo- zoic, or Mesozoic. Precambrian age suggested by similarity of quartzite conglomerate to that in micace— ous schist and quartzite of known Precambrian age in Panamint Range about 80 miles northeast (Wright and Troxel, 1954, p. 24, fig. 9). In Oro Grande Formation, crinoid fragments sug- gestive of Carboniferous age from limestone marble 311;, miles northeast of Oro Grande and 2% miles northeast of Victorville, reported by Miller (1944, p. 99—100, fig. 6); brachiopod and crinoid debris of Carboniferous( ?) age from upper part of limestone marble on Sparkhule Hill, and two poorly preserved brachiopods suggestive of Pennsylvanian age from top of carbonate unit (in WV), sec. 25, T. 7 N., R. 6 W.) in southeastern Shadow Mountains, reported by Bowen (1954, p. 34). Oro Grande Formation lithologically similar to Furnace Limestone (Vaughn, 1922, p. 344, 352—365, map) in San Bernardino Mountains from which crinoid and other fossil fragments of Carboni- ferous (Mississipian?) age are reported by Wood- FEE-TERTIARY CRYSTALLINE ROCKS 29 R 7 w R. a w by ‘7 27 26 25 so 29 26 NORTH TUNGSTEN 90 FITS 0 . . 35 0 V1 1 MILE EXPLANATION Alluvial sediments QUATERNARY Granite and aplitic dikes 2 x / ‘1’ B / \, \ 8 Quartz monmnite lg ¢\\ 3‘ =I\" Oro Grande (7) Formation Dolomite and limestone SEA LEVEL SEA LEVEL Homblende diorite 5 D : O ,_— [I _: Lu E Homfels Schist Quartzite g m n: < 0 Bl 4000' 2000' SEA LEVEL SEA LEVEL FIGURE 16.—Ge010gic map and section of northern Shadow Mountains. OR OLDER 3O AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA R. 6 W. N \ \ 20\ \ \\\ \\\-\-. ‘ \\ \\\\\ \ \\ \&\\;\;x\21\\ 0 ‘EX‘MMW \ \ \“50'/" RM \ l! H _. \ I l||\ \ \\ R- 5 W C "‘1 a 1 \ 30 2: 50 .“ . qu E . ' W4 , We \ \ #0 ‘- 1‘ Kb! \\ 2 \\ I l +> \f.“ 31 \I \ \,\\ ‘.‘\\\ r. '\ \ 7 ’\' \ N, (04”? //\I ‘ n' \\ 30 T. \ 6 \ \\ N \ . C \ s ‘3 5 EXPLANATION l K m >- n: D II Alluvial sediments 3 Z z—w qu ' 9 7 ‘1 2 4 Granite and Quartz mus- 8 _ % aplitic dikes covite dike g \ I — '5,\ l5 \ ’ 55 ’ / / / V\\< 0 1k 1 MILE Quartz monzonite [I L“—‘—’ o W N 45 0 O 5" Homblende dioritg g g < Quartz latite porphyry g = 1'“ — i ‘3' g g 4]- 1 o g 522‘ ‘ , - “o z z s Limestone and Hornfels Schist Quartzite '1 r: o g . < u g E ‘“ dolomlte o u. g 3 AI — \ , ' ‘ / — 2000' SEA LEVEL SEA LEVEL FIGURE 17.—Geologic map and section of southern Shadow Mountains. PRE -TE RTIARY CRYSTALLINE ROCKS R,2 w ,\‘ +\/ -f,’\ EXPLANATION > 33 :l:l\ + E “ “’ « . E E 6 > \|:\/,\ \A Lu ,\ \1 \ N' “ "H ‘” Alluvium LE “’ I l > 1 D T. U I < i /\ \-\ \ r 4 0 v M "y in“ WW N‘ 325453: ‘ ’\ l 30 fs e \I:] "5"“: \- / ¢ :5 ‘ o \ _-__¢\, Massive Coarse Diorite Q - . -= J" ‘ s a“ \ “52’ " porphm porphyry porphyry 0 ‘4 {1' ’ ‘7‘," a): breccia 8 . ‘ ‘ I X ear/’3 ¢ m " § “’65 $517k: 9/50 s‘s runszcown 1.1 /¢” I ’70 ”<-’,§ la’ MARBLE 2 § ’5:’ (9/4": \’\,§ QUARRY + \‘s-‘v y¢§§’\gig§:§" ‘ 4” ..... ’,0¢¢’\¢§I =I§ Granite \0 ........... § § § ...a§ ’ m ‘ =1 " I! . 9-H y a @: I \ I1..¢l\,.l - f. 1r VL‘T‘I 00 é \ ~ \I 4 r \\/l , NJ 9 = ’10 ¢ t 4 v L , - - \ 00 ¢ '9 g , m P c N a / ’ a , Granite and quartz Biotite-rich quartz lug ' monzonite monzonite E < ,- .-. 3’95 anono E 2 33:13 ooooa -05 z 3% a on o o 2 Z: .-.._ “(at a a In >62, Dolomite conglomerate 1&1 iii C , «T. V: Z' w c U) E E 0: au °' “30 eg . _ 5:: g h Limestone Schist U E FIGURE 18,—Geologic map and section of northernmost part of Sidewinder Mountain. ford and Harris (1928, p. 270), and Mississippian fossils found by J. F. Richmond (1960). Foregoing evidence indicates Oro Grande Formation of probable Carboniferous age. Bean Canyon Formation and other metasedimen- tary rocks in Tehachapi Mountains and southern Sier- ra Nevada lithologically similar to each other and to Oro Grande Formation and therefore may be correla- tive; thus most likely of late Paleozoic (Carbonifer- we?) age. In Garlock Formation of El Paso Mountains, cri- noid stems and fusulinids found in pebbly impure platy limestone at base of unit 12 near Goler Canyon; fusulinids identified as Schwagerz'm sp., of Permian age; because of absence of Parafusulina, unit 12 be- lieved to be Lower Permian (C. W. Merriam, in Dib- blee, 1952, p. 19, footnote). No other diagnostic fossils found; crinoid fragments found in units 16—19; units 13-22 probably Permian, possibly in part younger; units 1—11 unfossiliferous, probably pre-Permian but presumably late Paleozoic in age. Upper part of Garlock Formation (units 12—22) probably younger than Oro Grande and Bean Canyon Formations and unnamed metasedimentary rocks. In Fairview Valley Formation, except for two local- ities, fossils found only in limestone conglomerate of Black Mountain, and nearly all in limestone clasts; 31 therefore, they only indicate age of source rock of clasts. Fossils collected by Bowen and H. R. Gale at Black Mountain mostly corals, brachiopods, gastro- pods, fragments of echinoids and crinoids, and few bryozoa, known from rocks of Cambrian to Permian ages, mostly Mississippian to Permian; more common fossils listed by ‘Bowen (1954, p. 42) as follows: Fossils from limestone conglomerate of Fairview Valley Formation, Black Mountain [Occurrenem a, abundant; c, common; 1‘, wire] M eekopora sp ____________ Composita sp ____________ spira. Echinocn'nus sp __________ Archeocidaris sp _________ Mississippian to Penn- sylvanian. Mississippian to Per- mian. Mississippian to Penn- sylvanian. Late Paleozoic _________ Name Known age range Occurrence Bellerophonids __________ Ordovician to Permian- - a Straparoids _____________ Silurian to Jurassic _____ a Raphistomids(?) _________ Ordovician to Silurian--- a Chonetes granuh'fera Pennsylvanian to Per- c (Owen). mian. M eekella sp ------------- Early Permian --------- r Herttchia sp. (Waageno- Permian --------------- a phyllum). Polypora sp ------------- Late Paleozoic --------- c Aulosteges sp.(?) --------- Permian --------------- a Omphalotrochus whitneyi--- Early Permian --------- c Omphalotrochus obtust- Permian _______________ r c 32 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA R.3W. “\'\\ \ Sax ‘\ 1 ~ ..\\\ Q ‘ . (l WW .5 l\ t \\\\\l '2 .\\ Z \‘\\\-\\ ( (E \ ta \ \\\\ ,. \ A at: EX F’ LA N AT | O N D: g < Alluvium and terrace gravel E a a <( ° 3 < . 0 Older alluv1um l‘v / l L‘, Quartz monzonite \ U (I — UJ \- L / k l O D I. > r \7 >N _l . 9.0 : Granite and quartz monzonite LLI n: I, E O A Hornblende diorite a E i; = U Q) _ —_ _ _ E '2 E U — O a N _ A _. N 5 E o 2 g: Marble Schist E O l N T 0 b 1 MILE L_ __ ___l __ _4 ‘ u N- 2000’ SEA LEVEL FIGURE 19.—Geologic map and section of Juniper Flat area, northwestern San Bernardino Mountains. Fossils reported by Bowen (1954, p. 41) from two localities less than a mile west of Black Mountain in thin conglomerate lenses in hornfels of lower part of Fairview Valley Formation included only small gas- tropods and Syringopom( ?). Fossils from limestone clasts in conglomerate of Black Mountain indicate 'Fairview Valley Formation may be Permian or younger, possibly Mesozoic, but it is older than plutonic and hypabyssal rocks of Meso— zoic age that intrude it. Fairview Valley Formation either correlative with or younger than upper part of Garlock Formation which it closely resembles litho- logically. METAVOLCANIC AND HYPABYSSAL ROCKS HODGE VOLCANIC FORMATION Sequence of metavolcanic rocks exposed between Iron Mountain and Mojave River near Hodge (pl. 1) ; described and mapped as Hodge Volcanic Formation by Bowen (1954, p. 34—36, pl. 1). Plutonic as well as volcanic “assemblage described and mapped by Miller (1944, p. 79—98) as Hodge Complex. Hodge Volcanic Formation composed of at least four rock types :- quartz latite-dacite porphyry, schis- tose quartz latite, sericite or muscovite schist, and quartzite (fig. 7). PRE -TE RTIARY R.3W. R.2W CRY STALLINE ROCKS 33 \\3\ \ \\7?\ \§ \u\‘= \ § a » \1 \ ass 9 a \ \ fi.\\=\$~ EXPLANATION V\u \Q$\ \\ \ - Q‘§\-\- '._ _‘_ §\\u ‘-\§ ‘5‘: E .\B\ § \ - \\\‘\\ ‘ < _ 5.553% S‘s: Alluvium z . .\\o\\l= “*9 ks E \ _ . \§ _ , . 7.. ,_ \'I\\',“°~°:. § .\\\\-\ \\ .\. '_ '_ § Older alluvium O \ \ \ ‘\. \\\' .\ .\~ . \ - :\\ “\\ 753x -\ . . , \ \ \ \ \\ Porphyritic felsite dikes U 0: Q; ‘.\\\\\\ éfib‘ _ _ 6 g 12 ,/\5\>.\:1,Z‘-7..\ _ :9 &§_% ““3: V > v 8.! N 4“." 5s lk'i’ 9 Q _ =L‘a 4 a \N < > r u) 0 —— In 109‘ ;§ / Massive Schistose Diorite Granite 2 a: {\0 Q\ Q 0 (o q a" porphyry porphyry porphyry and 9 § quartz \ fi$2 Q monzonite . [’5‘ .5 \\ x . >. RESERVE' QUARR 7 Q 0 0 “a ‘7 '7 I 3 {Q > 7 ll 0 b 75 E Limestone co lomerate Z 2 o w 1 MILE fl § I, > :3 ng S D < ‘ 17 J 3 2 z — E 5 5:. E < E A, .3 {:4 _—F: m m D. k‘ Homfelsic Hornfelsic Pebble limestone argillite conglomerate 4000' 4000 o u.- -:: ‘3 _ _ {3 5 g E m 2 (7, 5 E -- — 83 E o Limestone Tactite Quartzite 11:2 2000. 2000, o a- marble 5 m SEA LEVEL SEA LEVEL FIGURE 20,—Geologic map and section of Black Mountain area near Sidewinder Mountain. Quartz latite-dacite porphyry massive, nonfoliated, dark—brownish gray; composed, in order of decreasing abundance, of subrounded, partly resorbed phenocrysts 1—3 mm in size of plagioclase (oligoclase), orthoclase, quartz, and biotite, that make up 20—45 percent of rock mass, in aphanitic groundmass containing iron oxides. Schistose quartz latite dark-greenish, purplish to brownish gray. Sericite, muscovite, and biotite present in variable amounts in groundmass. Sericite or muscovite schist a heterogeneous unit ranging from dark schistose quartz latite to light- colored sericite or muscovite schists. Tan to cream- white schists, very highly foliated and fine grained, composed almost entirely of sericite, muscovite, and finely divided quartz. Quartzite light tan, massive to faintly bedded, fine grained; composed entirely of quartz; slightly to se- verely brecciated but recemented by limonite and hem- atite. Rock commonly stained yellowish to reddish brown. Occurs as lenses in sericite or muscovite schist sometimes as much as 50 feet wide and 2,000 feet long. Formation probably metamorphosed from sequence of extrusive lava flows and pyroclastic rocks, possibly from some intrusive rocks. Age mainly Mesozoic, and as old as Permian( ?), but probably younger than Oro Grande Formation. PORPEYRY COMPLEX Porphyry complew of area east of Mojave River.— Porphyritic rocks of mainly latite or andesite com- position extensively exposed from Mojave River east- ward to and beyond east border to mapped area (pl. 1). Rocks described and mapped by Miller (1944, p. 100—102, pl. 5) and called Sidewinder Valley Meta- voloanics (late Paleozoic). Called Sidewinder Vol- canic Series (Triassic?) by Bowen (1954, p. 42—43, 68—72, pl. 1), but intrusive rocks near Stoddard Well mapped by him as quartz monzonite porphyry of Jurassic to Cretaceous age. Beyond east border of mapped area called Ord Mountain Group (Triassic) by Gardner (1940, p. 266—270, pl. 1). Because of complex and controversial field relations, lithologic terms only, rather than formational names, applied to these igneous rocks in this report. Porphyry complex consists of three lithologic units differentiated and described on quadrangle maps 34 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA R, 38 E, R, 39 E. // l/ «\/f_ \‘l'I/I .-'/ E FIGURE 21.——Geologic map of central PRE-TERTIARY CRYSTALLINE ROCKS R. 39 E. R, 40 E, \:\\\§\ \“s‘rfi \’«\ , \\\ \ '\\§\\\\\\\\ § / \q’?’ ’\ \\§\\ Slate and phyllite Garlock Formation (stratigraphic units 1-22 in ascending order) Schistose slate Mesquite J Schist I and eastern El Paso Mountains. Granite w“ \/ \ ’1’ /:I\\: Quartz monzonite ix /\ AV < 4 Gneissoid quartz monzonite // 1/ I1‘;” Quartz diorite // // ll \\ uf\ Porphyry complex EXPLANATION C] Alluvium E Older alluvium and terrace gravel V MESOZOIC Black Mountain Basalt Ricardo Formation 00 00° Goler Formation M v MESOZOIC AND OLDER E a.” ° 0 o c o _._, M Pebble Limestone Hornfels Tactite Z ‘3 conglomerate g Q E z _ - [I < E ’ -, 0 Q 0 l] l] , Lu 5 , A § 0 a a . 0‘ n. Chert Chert pebble Sandy Greenstone Andesibe J conglomerate limestone (meta basalt) porphyry ;_ E w i “IJ < we; - M f D: a: “‘7 1 Fa m Schist Limestone and E schist S W OUATERNARY TERTIARY AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 36 dozafihoh “32.56 mo BE: 8 name» 9355.4 AN 8:»: 5 562m v.8 328% no 98558: $55582 36% an no muoSowwldm ":5ch Jw>w4 (mm Jw>wn_ (mm \\ “ : : __ /M Q / om / / 2 / // //// 22 2/ ////7// B // f2 ///2/ 3 éll/¢ mH/a/s & 2 5/ ~88 \\ =/ u = = // \= \\ = 0 __ // u/ n ¢ : / / //\ \a// /////M// 1/ w// // A/n/Mfi ’\////// ///////// ///.//// // II/ Il/fl né///, § § & .88 ,, n H \\ \ ,, Q = g V, /, .. \/ 56 \.////2//é/fl,7£fl€ \/<w4 (mm Jw>w4 (mm H : ¢ \ ll // W H \ : fl. / / 3/ / / // H 4 \ 4 \\: / // .. / / z/ \ // / = o 2 .fl/zxfi/{m ,. S..// a , w n /m/ w m a \\ a n .88 0 // ,/ 0.. . // / / //... ¢\\\\ / //// 0/ 7% o/ 4 \\ \ // .88 q a o I /m///,Hw~y///o / OWMWflA/W/x/éks IAN/074 9/ LL ,, \, , Q x,“ \ : a I fi/ ////mV//o / .. /// 7/” ////// 0800/” 0/7//// p > 4 \ l “ ¢ 4 \\ r . o 7... //////fl ////\o\\\\\\ 7/////// 4<<>L \\ ,,\\“,, // //I / //\\\\\\\\\o y//////////// < <78 4/ \\ __ \\ \\ 08M“ x \xxx M/fl’ ’ 7 > >><> >L / vices uoKuea annbsaw FEE-TERTIARY CRYSTALLINE ROCKS 37 (Dibblee, 1960a, 1960e, 1960g) as porphyry, porphyri- tic felsite, and tourmaline-quartz-muscovite rock. PORPKYRY Porphyry ranges from latite and andesite (predom— inant) to quartz latite and dacite (subordinate); phenocrysts constitute 10—50 percent of rock, range from 1—4 mm in diameter. Groundmass medium to dark gray; weathers brownish gray; aphanitic to fine grained. Phenocrysts generally subrounded, partly resorbed; composed of plagioclase (sodic andesine), orthoclase, biotite, hornblende, and quartz, in order of decreasing abundance, some or all of last four not everywhere present; biotite and hornblende partly or wholly replaced by magnetite and chlorite in many rocks. Groundmass probably composed of same min- erals present as phenocrysts, as well as quartz, sphene, magnetite, epidote, and chlorite. Remnants of shards( '9) and other minute fragments visible in groundmass in many )thin sections suggest rock may be in part a metatufi‘ (A. O. Woodford, oral commun., 1959). Crys- talline epidote commonly present as veinlets, fracture coatings, and small rosettes within rock. Porphyry composed of following lithologic facies, all gradational into each other, as shown on quadrangle geologic maps (Dibblee, 1960a, e, g): (1) massive porphyry, (2) diorite porphyry, (3) chloritized por- phyry, (4) schistose porphyry, (5) fine porphyry breccia, (6) coarse porphyry breccia, (7) metatufl’, and (8) felsite agglomerate. Massive porphyry—Massive, most widespread facies of porphyry; forms large masses and some narrow dikes; contains relict spherulites as large as half an inch in diameter. Diorite porphyry—Exposed 1 mile south of Black Mountain and 3 miles west of Stoddard Well and in hills just north of Stoddard Well (Dibblee, 1960d). Dark-gray dioritic facies of porphyry; phenocrysts consist only of plagioclase and hornblende; ground- mass fine to medium grained, composed of plagioclase, orthoclase, hornblende, and magnetite. Chlorz'tized porphyry—Exposed mostly at Stoddard Mountain southwest of Stoddard Well (fig. 23) and on the mountain 3 miles southwest, and on Silver Moun- tain (Dibblee, 1960g). Dark-gray to nearly black schistose, somewhat mafic facies; contains ferromag- nesian minerals largely altered to chlorite and biotite, and indistinct plagioclase phenocrysts. Schistose p0rphyry.—Facies exposed along western margin of the hills within 3 miles southeast of Helen- dale (Dibblee, 1960g); in hill 1 mile west of Side- winder mine (fig. 20) and northwestward for 4 miles (Dibblee, 1960e) ; on west slope of Stoddard Mountain and on Stoddard Ridge (fig. 23). A light-colored facies containing indistinct phenocrysts; groundmass weakly to intensely sericitized; locally chloritized. In places altered to sericite-quartz schist, in others almost completely silicified to rock resembling quartzite. Fine porphyry breccia—Exposed in hills 1—2 miles southeast of Helendale, on low ridge west-southwest of Stoddard Mountain (Dibblee, 1960e, g), on Stod— dard Ridge (fig. 23), and near base of Sidewinder Mountain (Dibblee, 1960c). Porphyry has sparse to numerous angular fragments of tan, brown, or gray felsite about an inch or less in diameter; fragments alined in places to suggest volcanic bedding or flow structure; locally somewhat schistose. Coarse porphyry breccia—Fades present as east- trending strip on Sidewinder Mountain (fig. 18) ; dark gray, composed of unsorted angular to subrounded fragments of porphyry from less than 1 inch to sev— eral feet in diameter; matrix schistose; some lenses of chert and silicified breccia as much as 10 feet thick. Metatufl.——Exposed in Silver Mountain area (Dib- blee, 1960g), 2 miles east and 2 miles northeast of Sparkhule Mountain (figs. 14, 15). Massive White to gray-white hard to chalky microgranular rock presum- ably composed mainly of quartz and sericite, possibly some feldspar; rock closely fractured and iron stained on fracture surfaces. Some layers are breccias with fragments of felsite; others are altered to powdery white aggregate of sericite and quartz. Falsite agglomerate.—Facies exposed as lenticular body 4 miles northeast of Oro Grande (figs. 14, 15). Poorly bedded or nonbedded accumulation of angular to subrounded fragments as much as 4 inches in length in gray-brown fine—grained matrix; most fragments gray-white to light-gray felsite; locally in basal part fragments light—gray quartzite; matrix volcanic to arkosic, in places replaced by epidote. PORPHYRITIG FELSITE Exposed in hills northwest of Sidewinder Valley, on Stoddard Ridge, at northeast base of Sidewinder Mountain (Dibblee, 1960e), and in hills north of Stoddard Ridge. Quartz latite to rhyolite in com- position, tan to pale pink, massive felsitic to porphy- ritic having aphanitic to finely aplitic texture. Pheno— crysts as much as 2 mm in diameter, form 10 percent or less of rock mass; most are plagioclase (oligoclase— andesine), others are orthoclase, quartz, and biotite. Ground-mass same minerals as phenocrysts, plus hema- tite, magnetite, sphene, apatite, [and zircon. Piedmont- ite reported by Bowen (1954, p. 51) may imp-art pink color to rocks on Stoddard Ridge and Sidewinder Mountain. Rocks generally unmetamorphosed. 38 \1 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Stoddard Mountaln 19 KEYSTONE MINE 3000' In ”I": _/ \r' ~| l, 4L L74A) 4 L44 Granite and quartz monmnite 1‘7; 72 ll ll f‘ /r - , = . ‘ n . // 4; Biotin-rich quartz monzonite EXPLANATION Alluvial sediments HYPABYSSAL IGNEOUS ROCKS ' "‘mmmm... ""‘V‘HIHL w Tourmaline-quartz- ‘\ muscovite dikes Aphmitic to porphyritic felsite 0' Veins A V q A i/fl Fine porphyry Chloritized breccia porphyry METASEDI MENTARY ROCKS L Marble FIGURE 23.—Geologic map and section of Stoddard well area. W OUATERNARY MESOZOIC PALEOZOICU) OR OLDER FEE-TERTIARY CRYSTALLINE ROCKS 39 TOURMALINE-QUARTZ-MUSCOVITE ROCK Described as “tourmalinized quartz porphyry” by Bowen (1954, figs. 28, 29). Crops out 2 miles south— west of Stoddard Well as two north-northeast-trending dikes as much as 50 feet wide (fig. 23). Rock gray white, hard; composed of fine-grained aggregate of quartz and muscovite with numerous rosettes 1—2 mm in diameter of finely crystalline blue-black tourmaline; rosettes contain limonite, probable alteration of pyrite, imparting brown stain to rock. Porphyry complex of Boron area.———Exposed in low hills just north of Boron (fig. 46). Gray-White mas- sive porphyry of quartz latite composition containing subrounded phenocrysts as large as 5 mm in diameter of quartz and feldspar; phenocrysts make up 10—15 percent of rock mass in a fine-grained aplitic ground- mass of plagioclase (oligoclase), potassic feldspar, quartz, muscovite, biotite, and hematite. Rock com- monly iron stained on fracture surfaces. Porphyry complex of El Paso Mmmtazins.—Exposed between Iron and Goler Canyons in the El Paso Moun- tains (fig. 21). Porphyry dark gray; massive, except at southwest margin of outcrop where it is locally brecciated and crudely schistose. Andesite composi- tion having phenocrysts of plagioclase and altered hornblende in finely crystalline groundmass. Pheno- crysts make up 20—30 percent of rock mass. FIELD RELATIONS, ORIGIN AND AGE In areas east of Mojave River most facies of por- phyry complex are of hypabyssal origin and are intrusive into Oro Grande and Fairview Valley For- mations and into older plutonic rocks of Mesozoic age; all facies are intruded by quartz monzonite of Cretace- ous age. Extrusive facies apparently overlies Oro Grande Formation east of Quartzite Mountain (figs. 14, 15). Porphyry complex is therefore mainly of Mesozoic age, possibly as old as Permian, and as young as Cretaceous. Dikes and most large bodies of massive porphyry intrusive, but some large masses may be extrusive. Diorite porphyry intrusive; metatufl' and felsite ag— glomerate probably of pyroclastic origin; other facies of porphyry either intrusive or extrusive or both. Porphyritic felsite of hypabyssal intrusive origin. In Boron area, porphyry complex forms small masses engulfed in Mesozoic quartz monzonite. In El Paso Mountains, porphyry complex forms sill-like mass emplaced in Garlock Formation, but may be in part extrusive. QUARTZ LATI’I'E FEL‘SITE Quartz latite felsite of Victorm'lle area.—Felsitic rock exposed 3 miles northeast of Victorville in north- trending strip (pl. 1) described and mapped as mixed Oro Grande and Sidewinder Valley by Miller (1944, p. 102, pl. v) ; included in Oro Grande Series by Bowen (1954, pl. 1) ; differentiated from it by Dibblee (1960g). Forms pendant in plutonic rocks. Rock dark gray, massive to slightly schistose, micro— crystalline; composed of potassic feldspar, plagioclase (oligoclase-andesine), quartz, biotite, hornblende, and hematite; in places contains very small phenocrysts of plagioclase. Quartz latite felsite of Kramer Hills. —— Felsite (mapped as hornfels by Dibblee, 1960d; included in Sidewinder Volcanic Series by Bowen, 1954, pl. 1) forms northeast-trending pendant 1 mile wide and 4 mileslong on quartz menzonite in eastern Kramer Hills (pl. 1). Felsite light gray; weathers brown; massive to faintly laminated, very fine grained; composed of quartz, potassic feldspar, calcic plagioclase (labra- dorite and bytownite), epidote, biotite, hematite, and magnetite, in order of decreasing abundance. Age presumably Mesozoic. RHYOLITE APLITE Rhyolz'tc aplz'te of western El Paso Mountains.— Exposed at and near lower Redrock Canyon at south- west end of El Paso Mountains (pl. 1, fig. 63) ; origin- ally mapped as granophyre (Dibblee, 1952, pl. 1, p. 33—34), intrusive into quartzite conglomerate and horn- fels; rock light gray; weathers buff; very hard, mas- sive, very fine grained; contains scattered small round phenocrysts of quartz and feldspar (less than 2 mm in diameter) . Age presumably Mesozoic. HORNBLENDE SCHIST AND GREENSTONE Hornblende schist of Kramer Hilla—Exposed on north flank of Kramer Hills east of US. Highway 395 as pendants in quartz monzonite. Rock gray black, massive to indistinctly foliated, fine to medium grained; composed of about 65 percent hornblende, 25 percent plagioclase (andesine), and 10 percent orthoclase, quartz, and iron oxides; weathered and weakly coher- ent. Age presumably Mesozoic. Hornblende schist and greemtone near Mirage Lake. —Exposed on a hill 2 miles southwest of Mirage Lake (fig. 24). Greenstone dark olive green, massive, fine grained; composed of antigorite or serpentine containing specks of magnetite; in places abundant veinlets of calcite, and some pseudomorphs of antigorite after coarsely radial crystalline actinolite or tremolite. Hornblende schist (or gneiss) gray black, medium to fine grained, homogeneous but with crude foliation; 40 R.7 W. 17 N' AVENUE P Black 19 Mountain AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA EXPLANATION E Alluvium >LL 14" H—1 QUATER- NARY Quartz monzonite Homblende granite Homblende diorite V s E PRE TERTIARY ”17"”: I, III I ,u’ % Homblende schist Greenstone Biotite schist 3i Garnet 'te FIGURE 24,—Geologic map and section of hills southwest of Mirage Lake. composed predominantly of hornblende, much plagio- clase (andesine), and some iron oxides. PLUTONIC ROCKS Plutonic igneous rocks constitute the major part of the exposed pre-Te-rtiary crystalline complex in the Mojave block. They crop out in the Sierra Nevada, and in the western and central parts of the Mojave Desert as far south as the San Bernardino and San Gabriel Mountains. The rocks are generally of medium-grained (3 mm average grain size) granitoid texture, and range in composition from granite to hornblende diorite or gabbro. Predominant plutonic types in the Mojave block are light-colored massive homogeneous quartz monzonites. The following lithologic units were recognized: (1) hornblende diorite and gabbro, (2) quartz diorite, (3) ferruginous syenite, (4) aplitic quartz monzonite, (5) gneissoid quartz monzonite, (6) biotite-rich quartz monzonite, (7) granite and quartz monzonite, (8) quartz monzonite, and (9) granite. Age relations of the first seven units are undetermined, but presumably they are contemporaneous (Mesozoic or older?). The last two units are younger and are of Mesozoic age. HORNBLENDE DIORITE AND GABBRO Rock exposed. in Gamble Spring Canyon, Tehachapi Mountains (fig. 12), in hills northwest of Barstow (fig. 5), at Iron Mountain (fig. 7), in central part of Shadow Mountains and Bell Mountain, in San Gabriel Mountains, south of Palmdale and Little Rock, and in northwestern San Bernardino Mountains (fig. 19). Rock dark gray to black, medium to coarsely crys- talline, nongneissoid; composed mainly of black horn- blende and white to lightwgray plagioclase. Horn— blende makes up 40—80 percent of rock; forms stubby to prismatic anhedra as much as 3 inches long; plagio— _ clase fills spaces between hornblende anhedra and ranges from calcic andesine to labradorite; consequent- ly rock ranges from diorite to gabbro. Biotite, diop- side, magnetite, apatite, and sphene commonly present in small amounts as primary minerals. Secondary minerals include green epidote, either as clusters of grains or as finely crystalline veinlets, clinozoisite, chlorite, and iron oxides. At Iron Mountain, rock mainly hornblende gabbro; feldspar gray labradorite (Bowen, 1954, p. 54—58). At Bell Mountain, rock highly mafic hornblendite; hornblende as much as 80 percent, remainder plagio- clase (labradorite), olivine (in part altered to ser- pentine and talc), diopside (in part altered .to chlo- ri'te) , magnetite, and epidote. In most places hornblende diorite and gabbro form ovate or elongate masses engulfed in and intruded by quartz monzonite (fig. 16), therefore older than quartz monzonite. Other masses associated with metasedi- mentary and gneissic rocks, commonly along contacts with quartz monzonite, elongate parallel to contacts PRE-TERTIARY CRYSTALLINE ROCKS 41 and to foliation of metamorphic rocks (pl. 1, figs. 5, 7, 12). These relations suggest that diorite and gabbro formed partly by metasomatism of metamorphic rocks during invasion of quartz monzonite in Mesozoic time. QUARTZ DIORITE Exposed extensively in western San Bernardino, San Gabriel, Tehachapi, and El Paso Mountains, and as small scattered masses in eastern parts of desert area. Grades from gray-white granodiorite composed mainly of plagioclase and quartz, minor but variable amounts of potassic feldspar, biotite, and hornblende, through quartz diorite, to medium-gray diorite com- posed mainly of plagioclase and hornblende. Quartz makes up as much as 30 percent of rock. Plagioclase (mainly andesine, less commonly oligoclase) makes up about half of rock. Potassic feldspar (microcline or orthoclase) seldom exceeds 10 percent of rock. Bioti-te also seldom exceeds 10 percent. Hornblende most abundant in diorite facies and in some places as high as 40 percent of rock. Accessory minerals, less than 2 percent of rock, are magnetite, sphene, apatite, and zircon. Secondary minerals, mostly in dioritic facies, are iron oxides (after hornblende and biotite) , chlorite (after biotite), epidote (after hornblende), and seri- cite and kaolinite (after feldspars), and veinlets of epidote. Quartz diorite generally gray and faintly to moder- ately gneissoid, especially in San Bernardino and San Gabriel Mountains and Tehachapi Mountains northwest of Garlock fault zone. However in Teha- chapi Mountains southeast of Garlock fault zone and in eastern El Paso Mountains, quartz diorite gray- white, nongneissoid, in part of granodiorite composi- tion, and physically indistinguishable from the quartz monzonite. Gneissoid quartz diorite younger than gneissic rocks of Precambrian(?) age which it intruded or from which it recrystallized. In area where it intrudes late Paleozoic metasedimentary rocks, must be post-late Paleozoic. Nongneissoid facies either older than, or contemporaneous with, quartz monzonite of Mesozoic age. In places where intruded by quartz monzonite, certainly older. FERRUGINOUS SYENITE Exposed in mountains southwest of Palmdale as mile-wide strip extending southwest from San Andreas fault (pl. 1); mapped and described as syenite and alkali granite by Simpson (1934, pl. 5, p. 385). Rock light brown to light gray, but stained brown by iron oxides where weathered; nongneissoid, medium grained, equigranular. Composed of 50—65 percent 239—655 0—67——4 alkali feldspar (mainly microperthite, also microcline and albite), 11—39 percent plagioclase (oligoclase), as much as 12 percent quartz, total of 7—9 percent hornblende, biotite, magnetite, hematite, and limonite, and less than a total of 1 percent apatite, zircon, and epidote. A few lenticular zones as much as 50 feet wide and several thousand feet long of dark-gray or brown syenite, rich in iron oxides. Ferruginous syenite much older than the Vasquez Formation of Tertiary age that unconformably over- lies it; may be same age as Mesozoic or older aplitic quartz monzonite into which it grades. APLITIC QUARTZ MONZONITE Crops out southwest of Palmdale, southwest of San Andreas fault zone, as a mile-wide strip trending north of east (pl. 1) ; mapped as monzonite aplite and quartz diorite by Simpson (1934, p. 384—385, pl. 5). Rock nearly white; weathers light tan; massive to gneissoid; ranges from fine-grained aplitic to medium- grained granitoid in texture. Contains many scattered elongate inclusions of biotite-rich banded gneiss. Com— posed mainly of quartz, alkali feldspar (microcline- perthite), and plagioclase (oligoclase) in about equal proportions, and total of less than 10 percent of biotite, muscovite, hornblende, iron oxides, apatite, and zircon. Aplitic quartz monzonite younger than the gneissic rocks of probable Precambrian(?) age that it either intrudes or was recrystallized from, and probably also younger than Pelona Schist. Much older than Tertiary Vasquez Formation that overlies it unconformably; probably emplaced or formed in Mesozoic time or earlier. GNEISSOID QUARTZ MONZONITE Crops out in two half-mile-wide strips, one east of Redrock Canyon and the other west of Mesquite Canyon (figs. 21, 22); formerly mapped as foliated granite (Dibblee, 1952, pl. 1, p. 34—35). Gray-white fine— to medium-grained gneissoid rock, about one-third quartz, two-thirds feldspar; a small percentage of biotite, muscovite, or sericite. Micas occur as finely divided parallel flakes in parallel clus- ters or streaks that give rock a gneissoid structure. Potassic feldspar (orthoclase or microcline) and sodic plagioclase (oligoclase) in about equal proportions in western exposure, plagioclase predominant in eastern exposure. In Mesquite Canyon area, rock in part is mylonitic, especially along contact with Mesquite Schist to east, and most of feldspar is sodic plagioclase. Gneissoid quartz monzonite younger than Mesquite Schist of Precambrian(?) age from which it may 42 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA have recrystallized or which it may have intruded; older than Mesozoic quartz diorite that intrudes it. BIOTITE-RICH QUARTZ MONZ ONITE Exposed in vicinity of Stoddard Well (fig. 23). Rock light to dark gray, somewhat mottled, nongneis- soid, granitoid. Composed mostly of quartz, potassic feldspar (orthoclase and microcline), plagioclase (oli- goclase), and biotite; less than 2 percent accessories (sphene, apatite, and magnetite). Plagioclase pre- dominates slightly over potassic feldspar; biotite forms 5—20 percent of rock as minute black flakes irregularly distributed as clusters producing dark mottlings; in places rock contains large but indistinct .phenocrysts of pinkish orthoclase; veinlets and disseminated grains of epidote locally common. _ Biotite—rich quartz monZOnite intruded by porphyry complex of Mesozoic age, therefore age Mesozoic or older. GRANITE AND QUARTZ MONZONITE Rock unit mapped as granite and quartz monzonite (Dibblee, 1960e) exposed in several areas east of upper Mojave River, mostly in Granite Mountains, and north- ward to Stoddard Well and Silver Mountain, in vicinity of Sidewinder Mountain, and in the low hills northeast of Sidewinder Valley. Unit gray white, granitoid, mostly nongneissoid, equi— granular, medium grained; weathers grayish to yellow- ish bufl' ; composed mostly of quartz, potassic feldspar (orthoclase or microcline) , and plagioclase (oligoclase) with slight predominance of potassic feldspar; very minor amounts of biotite, muscovite, and such acces- sories as sphene, apatite, and magnetite, and in places a little hornblende. Feldspars white to grayish white; biotite, which rarely exceeds 4 percent of rock in form of small scattered flakes, commonly leached pale brown, and may be partly or wholly altered to limonite which forms a brown stain. Rock strongly coherent but closely jointed; tends to form jagged, much-broken outcrops. Local facies of granite and quartz monzonite unit are: (1) A somewhat gneissoid facies, resulting from subparallel orientation of hornblende anhedra and biotite flakes; exposed in extreme southwestern part of the Granite Mountains. (2) A medium— to coarse- grained porphyritic facies containing large scattered rectangular phenocrysts of orthoclase as long as 2 centimeters; exposed in gap between two main parts of Granite Mountains. (3) A fine-grained aplitic facies containing small feldspar phenocrysts; exposed in extreme northern Granite Mountains, southern part of Sidewinder Mountain, Stoddard Ridge, and north- ward and westward nearly to Helendale fault. (4) A medium-grained facies approaching syenite and mon- zonite in composition; made up almost entirely of conspicuous rectangular grains of feldspar and very little quartz; exposed just north of Sidewinder Moun- tain and in the area about 5 miles southeast of Helen- dale. In Granite Mountains and north of Sidewinder Mountain, granite and quartz monzonite unit engulfs pendants of Oro Grande Formation, is therefore younger than that formation. In vicinity of Side- winder Mountain, aplitic facies apparently gradational into large masses of porphyry complex; if so, presum- ably same age. However, near Stoddard Well and in Silver Mountain may be intrusive into large masses of porphyry complex but intruded by dikes of that rock. Intruded by quartz monzonite of Cretaceous age. Therefore, age of granite and quartz monzonite Mesozoic, probably Jurassic or Early Cretaceous. QUARTZ MONZ ONITE Extensively exposed in western Mojave Desert be- tween San Andreas and Garlock faults, locally exposed north of Garlock fault (fig. 70) and south of San Andreas fault (pl. 1). In Randsburg mining district mapped as Atolia Quartz monzonite by Hulin (1925, pl. 1, p. 33-39) ; in Victorville area as Victorville quartz monzonite by Miller (1944, pl. v, p. 105—106), Bowen (1954, pl. 1, p. 65—68); at Liebre Mountain as Liebre quartz mon- zonite by Crowe‘ll (1952, pl. 1, p. 8—11); in Valyermo area as Holcomb quartz monzonite by Noble (1954a). Rock gray white medium grained nongneissoid granitoid, remarkably uniform in physical character throughout its great areal extent. Composed essen- tially of quartz, potassic feldspar (microcline or ortho- clase), and plagioclase (oligoclase or andesine) in nearly equal proportions, but with slight predomin- ance of plagioclase in some places, of potassic feldspar in few others; contains small percentage of biotite, usually as scattered black euhedral plates; total of less than 2 percent accessories (hornblende, iron oxides, sphene, apatite, zircon, and muscovite)». A slightly mafic facies, having com-position of grano- diorite; forms transitional zone 1/2--1 mile wide between normal massive quartz monzonite and gneissoid quartz diorite in several places; this facies, mapped with quartz monzonite on pl. 1 along northwestern margin of gneiss and associated quartz diorite of hills north and northwest of Barstow (fig. 5), along northern margin of similar rocks in San Bernardino and San Gabriel Mountains north of the San Andreas fault zone, and in mountains south of this fault zone in vicinity of Sawmill and Liebre Mountains. TERTIARY SEDIMENTARY AND VOLCANIC ROCKS Quartz monzonite Mesozoic in age. Lower age 1 limit of quartz monzonite, that of youngest rock unit i it intrudes, namely, hypabyssal and metavolcanic rocks of probable Mesozoic age, and granite and quartz monzonite unit of probable Late Jurassic or Cretaceous age in areas east of Mojave River. Upper age limit that of quartz latite dikes of Cretaceous or early Tertiary age that intrude it in Harper Valley area. Therefore quartz monzonite possibly Late Jurassic or more probably Early Cretaceous in age. Age calculations based on lead-alpha ratios in zircon content of quartz monzonite made on three samples by T. W. Stern (written commun., March 13, 1957, to D. F. Hewett and W. C. Smith) as follows: sample from center sec. 25, T. 8 N., R. 16 W., S.B.B. and M., west Antelope Valley 6 miles west of Fairmont, 86: 10 million years; sample from SW14 sec. 2, T. 9 N., R. 12 W., S.B.B. and M., Rosamond Hills 3 miles northeast of Rosamond, 95:10 million years; sample from NW1/4 sec. 31, T. 31 S., R. 43 E., M.D.B. and M., north Harper Valley 2 miles east of Fremont Peak, 85: 10 million years ( 90: 10 million years from mona- zite); sample from SW14 sec. 31, T. 5 N., R. 3 W., Granite Mountains, near Deadman Point 1121-10 mil- lion years (this may be from granite and quartz mon— zonite). These ages are all within the Cretaceous period. GRANITE Most extensive outcrops in the Tehachapi Mountains southeast of Garlock fault from San Andreas fault 21 miles northeastward, west of Mesquite Canyon in El Paso Mountains, in western Rand Mountains, in Bissel‘l Hills west of Rogers Lake, in hills east and southeast of Rogers Lake to Mirage Valley, in hills north of Sidewinder Mountain and 2 miles northeast of Victor- ville, and in vicinity of Fremont Valley near Koehn Lake. Mapped by Crowell (1952, pl. 1, p. 10) and Wiese (1950, pl. 1, p. 24—27) in Tehachapi Mountains. Granite generally pinkish cream white, nongneissoid, medium grained; composed essentially of quartz, potas- sic feldspar (orthoclase, microcline, locally perthite), and plagioclase (oligoclase); potassic feldspar pre- dominant over plagioclase in most places. Less than 1 percent accessory minerals (muscovite, biotite, apa- tite, sphene, zircon, and magnetite, in order of decreas- ing abundance). Granite occurs as stocks with numerous ofl'shooting apophyses and dikes of pegma-tite and aplite intrusive into quartz monzonite, quartz diorite, and older rocks. Granite Mesozoic in age. Most granite presumably slightly younger than quartz monzonite of Late J was- sic or Cretaceous age. 43 PEGMATITE AND APLITE Not shown on plate 1. Exposed in hills between Rogers Lake and Mirage Valley. Most widespread at Saddleback Butte and vicinity, 17—20 miles east of Lancaster (fig. 25; Dibblee, 19580). Other occurrences at Lovejoy Buttes (Dibblee, 1959a), hills north of Kramer (figs. 46, 47, and Dibblee, 1958a), hills west of Harper Valley, hills north and northeast of Gravel Hills, in western Rand Mountains, and in El Paso Mountains west of Mesquite Canyon. Rocks cream white with textures ranging from coarse pegmatite (grain size as large as 11/; inch) through graphic granite to aplite; dikes generally coarse in interior, finer along outer margins, commonly have textural zoning. Dikes composed essentially of quartz, potassic feldspar (orthoclase or microcline), and some plagioclase (albite-oligoclase); minor mus- covite and biotite; some dikes near Harper Valley contain hornblende, rarely black tourmaline, but lack more exotic minerals. Occur as dikes a few inches to a few feet wide, either scattered or in swarms, intrusive into quartz monzonite and adjacent older rocks. Probably represent final pulse of plutonic intrusion in western Mojave Desert. Possibly Jurassic but more likely Cretaceous in age. Age calculation based on lead-uranium ratio in euxenite from a pegmatite dike in quartz monzonite and hornblende gabbro determined as 72 million years, or late Cretaceous (T. W. Stern, written commun., March 13, 1957, to D. F. Hewett and W. C. Smith). HYPABYSSAL ROCKS QUARTZ LATI'I'E Quartz latite forms dikes, mostly loss than 10 feet wide but one as wide as 500 feet, in hills south of Boron (Dibblee, 1960d, p. 86—87), and in Fremont Peak area. Intrusive into quartz monzonite and older rocks, therefore not older than Cretaceous; quartz latite fragments present in Barstow Formation, there- fore not younger than late Miocene. Quartz latite most likely either Cretaceous or early Tertiary in age. Quartz latite white or pale bluish pink to gray, weathers tan; very hard, felsitic, massive to rarely faintly flow banded. Composed of microcrystalline potassic feldspar and sodic plagioclase partly altered to sericite, and traces of hematite. Commonly contains a few small phenocrysts of clear quartz, feldspar, and minute flakes of biotite. TERTIARY SEDIMEN‘TARY AND VOLCANIC ROCKS GENERAL FEATURES Deposits of Tertiary age in the western Mojave Desert region consist of a great variety of nonmarine sedimentary, pyroclastic, and volcanic rocks, and some 44 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA I Saddleback Butte 4000' 2000’ EXPLANATION Alluvium $1 QUATERNARY UNCONFORMI TV Pegmatite dikes /\7 / \— / Quartz monzonibe Saddleback \ Butte f: 28 27 ( 33 34 T 7 Q? N- ROAD T. 6 N. N 0 ‘6 PRE- D: . < Alluvxum z 0: Lu , l— :«g. g 0 Older alluvium $9 3.55 +.+:+:I g g 2:! f3 ’5 + + 5' m s s 23 5 ° . '3-3 > o E Reddlsh-gray sandstone and a E h‘ v gypsiferous shale E < ‘x 8 _ ‘ I— Q; ‘5 fl . I I... " E s g £2 3 ..- -. F s) Q o d; E . S e = 5 Buff arkosm Dark-gray w a; a E a f g: s E sandstone, shale and g g F“ V some can siltstone a ,‘n‘ glomerate \7 / <71: «17 — /V‘/ v ’ Z 4000 ‘ < Gneiss and E granodiorite III . E 2000 WM M 5 «1/ Lu 3; M E SEA °|____*lf—l M'LE Pelona Schist FIGURE 26.—Geologic map and sections of San Francisquito Canyon area. 46 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Clay shale dark gray; weathers brownish gray; well bedded, indurated, closely fractured, argillaceous to silty, highly micaceous. In places contains carbonized wood fragment-s. Commonly contains dark-gray flaggy hard calcareous layers few inches thick, and also dark- gray calcareous concretions. Sandstone forms hard massive strata from few inches to 20 feet thick; light olive gray; weathers bqu' to light brown, fine to medium grained, locally conglomeratic. Grains subangular, composed of quartz and feldspar (mostly plagioclase) , biotite flakes common. Conglomerate occurs as brown lenses and beds from a few inches to several tens of feet thick. Composed of well-rounded pebbles and cobbles in matrix of hard arkosic sandstone. Clasts composed of very hard rocks, mainly light—brown to gray felsitic and porphyritic igneous rocks, quartzite, granitoid rocks, pegmatite, aplite, and some gneiss. Local basal conglomerates composed of cobbles and boulders derived from under- lying gneiss and quartz diorite. Exposed sequences as follows in descending order: San Francisquito Formation in San Francisquito Canyon (fig. 26) Vasquez Formation: Sandstone and siltstone, reddish-gray; basal contact . conformable. Eatlmled _ _ . thickness San Francrsquito Formation: (feet) Siltstone and sandstone, interbedded ______________ 150 Sandstone; minor thin interbeds of shale ___________ 650 Shale; minor interbedded sandstone _______________ 350 Sandstone, a few lenses of conglomerate ___________ 350 Shale; grades westward into sandstone _____________ 250 Sandstone; thickens eastward ____________________ 100 Shale; grades westward into sandstone _____________ 400 Sandstone _____________________________________ 300 Shale; grades westward into sandstone _____________ 250 Sandstone, a few lenses of conglomerate; thins east- ward ________________________________________ 800 Shale; grades westward into sandstone _____________ 200 Sandstone; lenses out eastward ___________________ 250 Shale; grades westward into sandstone _____________ 200 Sandstone; several thin interbeds of conglomerate, siltstone, and shale, including a conglomerate lens about 20 ft thick 400 ft below top; thickens west- ward, thins eastward __________________________ l, 350 Shale; several thin beds of sandstone a few feet thick, except one 200 ft from top that is as thick as 50 ft; sandstone beds mostly in upper half, which grades westward into sandstone _______________________ 1, 300 Total exposed thickness, San Francisquito For- mation __________________________________ 6, 900 Unconformity, partly in fault contact. Gneissic rocks of pre-Tertiary age. San Francisquito Formation in Big Rock Creek and Devils Punch- bowl area (figs. 29, 30) Punchbowl Formation. Unconformity. San Francisquito Formation: ”“6an Upper part: mainly sandstone and abundant inter- (feet) beds of clay shale and lenses of conglomerate _____ 2, 000 Lower part: mainly clay shale; a few thin beds of sandstone; includes several thick lenses of sand- stone and conglomerate in most westerly exposures and thin basal lenses of sandstone and conglomerate Estimated on Pinyon Ridge ______________________________ 2, 000 Total exposed thickness, San Francisquito For- mation __________________________________ 4, 000 Unconformity. Gneissic rocks and quartz diorite of pro-Tertiary age. In Cajon Creek about 1,500 feet of lowest part of formation present, composed of shale and sandstone, 10 feet of basal conglomerate, on gneissic rocks, un- conformably overlain by Punchbowl Formation. Marine molluscan fossils characteristic of Martinez Formation of Paleocene age of Mount Diablo region, 450 miles to northwest, reported from basal part of San Francisquito Formation by Dickerson (1914, p. 295), from lowest 400 feet of beds on Pinyon Ridge. Similar fossils found in basal part in vicinity of Elizabeth Lake Canyon beyond western border of figure 30 by students from University of California at Los Angeles. Unfossiliferous middle and upper parts of this thick sequence presumably range from Paleocene into Eocene age. Therefore, age of San Francisquito Formation considered to be Paleocene and Eocene( 2). vssevaz FORMATION A sequence of terrestrial sedimentary and volcanic rocks of Oligocene and early Miocene( ’4) age, uncon- formable on pre-Tertiary crystalline rocks and uncon- formable below Punchbowl Formation in Soledad Pass area southwest of San Andreas fault (pl. 1; figs. 27, 28). Exposed more extensively beyond southwest border of mapped area where it was described as Escondido Series by Hershey (1902b, p. 350—355), but because name preempted renamed Vasquez Series by Sharp (1935). In Soledad Pass area, Vasquez Formation composed of volcanic rocks and minor amounts of sedimentary rocks. Volcanic rocks mainly andesite, a few ques- tionable variations to dacite and mafic andesite, and some basalt and tufl-breccia. Andesitic rocks pink to TERTIARY SEDIMENTARY AND VOLCANIC ROCKS R,IZ W R.“ W. - , \\ 4 3 ' - . . m | / \ . , l s ‘ e _ /' ‘n . < “v :2? I: don V95 (:‘5/3 (U N -L’::A:.\':I:/\7’/\:1’ LU do ‘U\‘,‘/\/I/,‘ \‘ ‘ ’ > ' \ \_ \ \ 1 l V I“ ’ wager ' ., ’ ¢::;::;;:.,. a»: T. 5 N, EXPLANATION E g .2 § ; E g 2 Gravel and sand E I: ,‘i‘ g 5 .5 g '1: . g 5—5 _ Granitic Schlst O ‘. f/L'q" .§ E fanglomerate fanglomeraw L , A <. . n.‘ and sand . H < uucouromwry ' l: ‘ Gray clay 9 o E — \ 2.24 "/‘DC/Pfiofi'l‘ffl ’ 1.. 3 "‘ Buff sandstone \fiCC’.‘ I“ K < E , 5 ' r3 \ Pink to buff sandstone UNCONFORMITV and conglomerate E I ° ’4 1 M'LE UNCONFORMABLE cm 5 1. m "' PLUTONIC ROCKS E E 9.: A " > .1 " > E >_ > S w a g .4 L: Andesite Toff g ’- §§ g 5 broccis breccia l: '5 1 Gray clay shale g: E E It! g 3 8 0 .§ 3 n " § 5: .8 t Basalt Sandstone r- : 1. 'fl 5 UNCONFORMIYY >. J I- § 0 '5' Sandstone Red clay __ ‘ / a: 3 \ / gs E a /\ l‘\\ “:1 S E E \/\I \/\ II I— ’- b 'g o a n: 5' (n a h Plumnic rocks E < If] IL a: Fanglomerate of l :3 D I volcanic detritus A < Z A 4000' “1 ( 0 z < Z < U) "JL" 4., \- " Al‘ F ”Pt/‘7]. _ <'~ ‘ \ \l \ /\/‘/\\l l » » /\\ \ \" ‘ ’ 7 —\ ~ — , ’~//\‘/‘/_\Q’_\’\/\/\/‘ J/_\/\m \ 1/ J10 \\/ _/,/,\ eJ/Ifi \\J/ 4/ /\/\/\;‘/\\\\‘\’/:\/?,\/‘/:‘/\IV.‘ \\ / \ W ,\\\,\ - , — \ ,Hu,‘ \_\ ;\| l/ ,/_ \\/)’_‘l\/ \ \/\/ \/,\ I / \ ,, [1‘ "/ "l\/\’\ - / /~‘//\\\ \_\\\’ l /,\/\ /\/\\—\\,\/\ x 7‘, — \, /,,\ \/ \ . ,l ,\ /\\ \\ l, l/,\/\/ ,x x \ \_\ \ ,M ,L I, \H “I,‘_/|\///\/\\//l<'/\/\Il\/7 I SEA LEVEL FIGURE 27.—Geolog'ic map and section of Cenozoic rocks of Soledad Pass area (in part modified after Wallace, 1949, and Noble, 1953). ' AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA R. H W. R. IO W. / 550 Granitic rock 1 2 at 520’ 625 G Granitic rock at 610' Limeg Rock a u u a 1 8 1 3 \/\ / l/ \ \/ ‘- l/\_ \ l \ NADEAU FAULTS ; SAN ANDREAS F ULT C NADEAU FAULTS ULT SEA LEVEL - 2000’ SEA LEVEL SEA NADEAU FAULTS SAN ANDREAS FAULT LEVEL FIGURE 28.—Geolog'ic map and sections of Cenozoic rocks of Little Rock area (in part modified after Noble, 1953). tian on figure 27. Explana- TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 49 dark reddish brown, massive, felsitic to slightly por— phyritic; contain scattered small phenocryts of plagio- clase, and, in places, a few of quartz, biotite, and horn- blende, in iron-oxide-bearing aphanitic groundmass. Basalt, black, fine grained; composed of plagioclase and augite( ?) ; contains scattered small amygdules of calcite or chalcedony. Tuff—breccia, unbedded; com- posed of angular fragments as large as a foot across of andesitic rocks and silicified tufl" in matrix of green- ish- to cream-white silicified or opalized tuff. Sedimentary rocks light gray, buff, red; composed of cobble-boulder conglomerate of granitic detritus, arkosic sandstone, and gritty siltstone. Deposited by streams. Vasquez Formation unfossiliferous. In San F ran- cisquito Canyon lies above Eocene(?) beds of San Francisquito Formation (fig. 26), therefore younger. In Soledad Pass unconformably underlies Punchbowl Formation; in Tick Canyon 12 miles west, unconform- ably underlies beds of early Miocene age (Jahns, 1940, . p. 170). Vasquez Formation therefore most likely Oligocene, not younger than early Miocene in age. VAQUEROS FORMATION Two small erosional remnants of light-gray con- glomerate and sandstone mapped as Vaqueros Forma- tion by Noble (1954b, p. 39—40) on quartz diori-te south- west of Cajon Junction north of San Andreas fault (fig. 31) contain marine molluscan fossils common in Vaqueros Formation of early Miocene and Oligo- cene( 2) age in Coast and Transverse Ranges. PUNCHBOWL FORMATION A sequence of terrestrial sedimentary rocks of upper Miocene and lower Pliocene age exposed in north- eastern margin of San Gabriel Mountains (pl. 1); unconformable on Vasquez Formation, San Francis- quito Formation, and pre-Tertiary crystalline rocks (pl. 1). Mapped and named by Noble (1953; 1954a) for section superbly exposed in Devils Punchbowl (figs. 29, 30), the type locality. In Devils Punchbowl area southwest of San Andreas fault, Punchbowl Formation lies unconformably on San Francisquito Formation; southeastward, laps onto Pelona Schist; about 5,000 feet exposed, top eroded (figs. 29, 30). Formation mostly thick~bedded buff white to locally pink medium- to coarse-grained ar- kosic sandstone; grades downward into gray to red cobble-boulder conglomerate at base; upward into medium-grained white sandstone and interbedded red to green siltstone. From LittleRock Creek to Soledad Pass (figs. 27, 28) about 2,200 feet of Punchbowl Formation exposed; mostly sandstone containing several lenses of red gypsiferous clay, and basal lens of fanglomerate de—1 rived from underlying andesite of Vasquez Formation.’ In Cajon Canyon area northeast of San Andreas fault, sequence assigned to Punchbowl Formation (Noble, 1954a; 1954b, pl. 1) unconformable on San Francisquito Formation and quartz diorite; overlain conformably by Crowder Formation (figs. 31, 32); sequence about 5,500 feet thick and lithologically al- most identical to Punchbowl Formation of Devils Punchbowl area. In nearly all exposures of Punchbowl Formation on both sides of San Andreas fault, clasts mostly of gra- nitic rocks, some of gneissic rocks, and few of Pelona Schist, San Francisquito sandstone, and Vasquez ande- site. Punchbowl Formation younger than Vasquez For- mation which it overlies unconformably. Scanty mam‘ malian fossil remains from lake beds just west of Little Rock Creek and from basal beds in Devils Punchbowl south of Valyermo, suggest late Miocene (Barstovian) age (Noble, 1953, and oral commun., 1958). Other remains found in all but basal beds of Punchbowl Formation of Devils Punchbowl area suggest early Pliocene (Clarendonian) age, whereas all remains found nearly throughout Punchbowl Formation of Cajon Canyon area suggest late Miocene (Barstovian) age (R. H. Tedford, University of California, River- side, oral commun., 1963). On basis of similar lithology and stratigraphic posi- tion above Vasquez Formation, Punchbowl Formation probably correlative in large part with Mint Canyon Formation (Kew, 1924) to the west, which also con- tains late Miocene (Barstovian) and early Pliocene (Clarendonian) mammalian faunas but which is over- lain by marine strata containing late Miocene (Moh- nian) foraminiferal and molluscan marine faunas (Jahns, 1940, p. 171—172; Durham, Jahns, and Sav- age, 1954, p. 66). On basis of foregoing evidence, Punchbowl F orma- tion here considered to be late Miocene and early Pliocene in age by vertebrate time scale. CROWDER FORMATION A sequence of fluviatile detrital sediments of mainly Pliocene age resting on Punchbowl Formation and on pre-Tertiary crystalline rocks and conformably over- lain by older alluvium in Cajon Canyon area (pl. 1; figs. 31, 33). Here named for Crowder Canyon, the type locality (Isl/2 sec. 13, secs. 24, 25, 26, T. 3 N., R. 6 W., fig. 31). Formation about 1,800 feet thick at Crowder and Cajon Canyons (fig. 32), thinning to northwest and 50 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 0 DA (V LI’fl-R /:\\:» _~ — 5L“ [1:53 ‘14— $37315“!- \ \\ \\\\ \ \\ \ ‘Tsf . "VI; K . \\ \ "$5 3 I Valyermo Ranch 9W. \ R,10 WV \ EXPLANATION x '0 0 O AHVNHELVDO 'c : 3 t 3 3v 3 a wg 3 a E .2 3 "'3 o 3: Eu 0 z 5 In 3 W x... ._J wnwuv (BOO) umymua ”PIC guaaag moo 43mg m .1 E $ 0 z ‘_...__ I: / AHVILHEL'HHd [a l') \ E II I .: x/ ‘n (X > 3 I f 2 \ O O— -E 3 a 5 ° T- m E .2 e e v 5 E g 3 13 D 5 5 .2 2 C5 AHVILHBL A 3 . E ,, o : E , a: e U s t Q ~ a» g 2° H g y. m 0 EB m a 'U ° 2 'U .5: g a. F‘ O = U) a: ° Eu :2 0 § J \ “ND (51) uopeuuog uopauuod Imoqqound oqgnbspmud u'es V V “439014.! new] PM) (2') ““903 W” masoyy Jaddn 314,990an FIGURE 29.—Geologic map of Devils Punchbowl area (modified after Noble, 1954a). TERTIARY SEDIMENTARY AND VOLCANIC ROCKS FAULT PUNCHBOWL 4000' “- ,\l 2000’ ,\,\ __.-r 4000' 6000’ m B’ 6000' a W , g: . § DeVIIs Punchbowl 2:; << . ~ ~ 21L . - ‘ < 4000. _ ‘ . [’1' m ‘ w I I ‘I ’t . ‘ \ u ’ f 2000' - U) a 6000' g: 22 (M. 2 < m 4000’ 4000’ 2000' 51 m E :5 E’ m» - 9? sooo' - 1§[;'\” ‘Illv \’ ”A l n ’1 I! - 4°00, \ / W"! WI>’>f\’;<;’t>?‘/;‘;”I'm/”r v I‘/\7\"“\/7 "slim! w ‘ \/f / W) Kf‘lp/(S‘lf) f? via); {\’{;f(?\/;/\/f; ‘/\\I\(j<7\\,\/j{l iL‘lu‘l W ‘l‘ l \\Hl \‘ ‘H - / \ / / / \ \ \ \ I \ § 2000- / // |\f/[\/i\/ \;\‘y\/ \/5\\,\/\\,\§/\\/\ \I \ H\\I\ll n ‘ “o u \\ _2000‘ \\I‘\// ‘\\\'/«\‘\' All A /\/\\\\\‘\I\,‘ g ,, ;\/,//u \ FIGURE 30.—Sections of Devils Punchbowl area. Locations of sections are shown on figure 29. 52 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA r 0 Alton Development Co 23 Sierra Nevada Oll Company - . . Yucca" \ OUATERNARY TERTIARY A Pleistocem Upper Miocene and Pliocene fi { , Older alluvium A Crowder Formation A Punchbowl Formation A E Alluvium 0 Terrace Landslide gravels rubble UNCONFORMITY r . a D Fanglomerate (Shoemaker Gravel) Sand and gravel L (Harold Formation equivalent) , Sandstone \ Fanglomerate Sandstone \ Conglomerate TERTIARY Oligocene (?) and Miocene Vaqueros (? ) Formation Paleocene and Eocene (.7) San fiancisquito Formation Sandstone and conglomerate (marine) UNCONFORMITV Siltsbone, clay, shale, and sandstone (marine) PRE-TERTIARY \ UNCONFORMITV 4/\ scp ~\ Q) / \ _ Quartz monzonite Quartz diorite -@ Gneiss Marble FIGURE 31.——Ge010gic Pelona Schist map of Cajun Pass area, o O n/ ,_ '. a _/Z 9/» o/'o° TERTIARY SEDIMENTARY AND VOLCANIC ROCKS Jersethlef '.I_"M.,..‘I 5’ ~ “:Tvb Canyon |¢|§II"’ ’ “lo... I I'O’§ 4 ug§ § - 1/ ' -'IH-I.4, . .un -'4¢'~ ‘,u ‘~ I“ ‘ / \,. _ \'. 2% ”a ‘°\30\‘ a '\ \ \ northwestern part (modified after Noble, 1954b) . 53 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Am Emma :o :32? 9% 98398 no 32930: .35“ mmwm 3.30 we msozowwlflm mascara / 31 I; g «<4 . . _.II .» ‘¢ u t v. .x. \ 4\ § ._ . ”luglsts as ‘ -u~— .~ ‘~ ;~‘ .. // X\\\\\\\ H.“ flx/MMWI/flvm/mrf 0 an” Aft .W/ / x/ .82 So us So .000? Q .mulw \ \ ///// //////aum _|\ \\\\.|./ \/\ now a §§ ”we/WWW“ \ a? 3 g, .88 .3. \\\\\\\ t“ /////w// /// n «411/» EL 2/ .. \\\\ // U/// // _/\// ///\/ cum \\\\ // fl//// // \\ \/_ \I. .83. / / /// Eu /_ \ / 8» Q ‘31..»5 .§-¢o- .~ .OOON ///I \r x, A. \\ \,/~I\ C/x .//_r\/f//~ \ .ooov / “firm? )xff SIC \\\\\\ / \ ~ \ I ,q if; ,éfi, — \ \ x. TERTIARY SEDIMENTARY AND VOLCANIC ROCKS southeast. Composed mostly of weakly consolidated sandstone and fanglomerate. Sandstone, gray white to bufl' White, friable, bedded, fine to coarse grained, conglomeratic, arkosic; contains scattered interbeds or lenses of pebble-cobble conglomerate and green to light- red siltstone. Pebbles and cobbles mainly of granitic rocks, some gneiss, felsite, porphyry, quartzite, schist, and quartz. Siltstone, gritty, sandy to argillaceous, in places containing small White calcareous nodules; 55 westward from Cajon Canyon siltstone is light reddish gray; eastward greenish gray. Fanglomerate massive to obscurely bedded; composed of unsorted boulders and cobbles of mainly granitic detritus in matrix of coarse arkosic sand. Crowder Formation younger than underlying Punch— bowl Formation of late Miocene and early Pliocene age, and older than overlying basal greenish gray sandy beds of older alluvium that are probably cor- Cum/‘- awa \ r - \ he ~'\ U |_\/\/\/-I \ \/ ‘17 EXPLANATION .f. ~\ \\/\ ”VHF, ’\l\/\l\1\} 70': g l Alluvium UNCONFOEM/TY > Terrace mvell g UNCONFORMITV E E o E 0»? S o § 0 E E leomerau E (Shoemaker Grnvel) i ‘ E 0 Gray gravel,sand, and silt (Harold Formation equiv-lent) 4000' § 5:, 5 _ .. w '5 § 3 g E: E Buff sandstone and > 0 ° I! '3 F“ red—brown ailutona < 2000' ‘3 F E .. i: B = m .§ 3 ‘3 i- : 5 E 5 ‘2 Arkoaic and-tone 9‘ (not exposed) UNCONFOEM/TY ‘WO‘ _\/ 3 \A’,“\ PRE- TERTIARY m 2: 7, /./ Gneiu and quartz diorite } 2000' FIGURE 33.—Geologic map and sections of Cenozoic rocks of San Gabriel Mountain foothill area near Mescal Creek (modified after Noble, 1954b). 56 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA relative with Harold Formation of Noble (Pleisto— cene) of Palmdale area; therefore part if not all of Crowder Formation most probably‘ of Pliocene age. ANAVERDE FORMATION Sequence of terrestrial sedimentary rocks of Plio- cene age exposed along San Andreas fault zone for about 28 miles northwestward from Little Rock area. Named and mapped by Wallace (1949, p. 790, pl. 1) after Anaverde Valley. Type section hereby desig- nated as sequence exposed 2—3 miles west-southwest of Palmdale (SW14 sec. 28, sec. 29 N1/2 sec. 33, T. 6 N., R. 12 W., fig. 34). Included in Escondido Formation (of former usage) by Simpson (1934, pl. 5). Formation consists of four main rock types: dioritic breccia, pink arkosic sandstone and conglomerate, buff arkosic sandstone, and clay shale. Dioritic breccia (“old arkose” of Wallace, 1949, p. 784, pl. 1) a severely shattered mass'of dark—gray medium- to coarse—grained diorite composed of plagio- clase, hornblende, and biotite; rock incoherent and deeply weathered; most northwesterly exposures com- posed of weathered fragmented diorite in crumbly red arkosic sandstone. Pink arkosic sandstone and conglomerate inter— bedded and intertongued; pink gray to bufl' friable, massive to poorly bedded; sandstone fine to coarse grained; pebbles and cobbles of conglomerate rounded, composed of granitic rocks, aplite, and pegmatite, in arkosic sandstone matrix. Bufl' arkosic sandstone grading to nearly white ;. friable to moderately hard, massive to bedded, fine to coarse grained, locally pebbly; in places contains in- terbeds of micaceous siltstone. Clay shale gray, soft, crumbly, thin bedded; con— tains veinlets and minute crystals of gypsum; in ex- posures 11/; miles southwest of Palmdale contains num- erous strata from less than 1 inch to several inches thick of white gypsum. Formation severely deformed (figs. 27, 28, 34) ; over- lies, and in fault contact with, pre-Tertiary rocks; top eroded; exposed thickness about 1,500 feet in San Andreas fault zone; possibly thicker in area 11/; miles southwest of Palmdale (fig. 34). Pink arkosic sand- stone and conglomerate forms lower unit; grades up- ward into buff arkosic sandstone, which in turn grades through interbedded sandstone and shale into over- lying clay shale (figs. 28, 34). Diorite breccia occurs as several discontinuous fault slivers southwest of Portal Ridge (Dibblee, 1961b). Nineteen species of fossil plants reported by Axel— rod (in Wallace, 1949, p. 791) from basal part of clay shale unit 31/; miles west of Palmdale (R. E. Wallace, 1959, oral commun.; fig. 34) are only fossils found. ‘ well (1952). Flora assigned to Hemphillian Stage of lower middle Pliocene (Savage and others, 1954, p. 53). An‘averde Formation lithologically similar to and possibly correlative with Peace Valley Beds of Cro- Supposedly younger than Punchbowl Formation to southeast, but lithologically similar and possibly in part correlative (Noble, 1953). PEACE VALLEY AREA PEACE VALLEY BEDS or CROWELL (1950) A lacustrine and fluviatile sedimentary sequence of Pliocene age unconformable on pre-Tertiary rocks and conformably overlain by Hungry Valley Formation in large area southwest of Liebre Mountain and east of Peace Valley (pl. 1). Described and mapped as Peace Valley Beds by Crowell (1950, p. 1631—1632, fig; 4; 1952, p. 13—14, pl. 1) and Jennings (1953, p. 9—13, pl. 1). Formation consists of clay shale, siltstone, sand« stone, and conglomerate. Clay shale and siltstone, gray, bedded, micaceous. Sandstone buff, well bedded, friable to hard, fine to medium grained, arkosic. Con— glomerate bufl' to brown; composed mainly of rounded pebbles and cobbles of granitic rocks, aplite, and peg- matite, plus few of gneiss, quartz, porphyry, and sand- stone. About 4,000 feet of beds exposed within mapped area, thinning and coarsening eastward; forms upper part of 18,000-foot sequence of Pliocene terrestrial beds exposed to south. Fossils found in Peace Valley Beds are fresh—water mollusk and smooth-shelled ostracods of no diagnostic age significance (Crowell, 1950, p. 1638), and stickle- back fish considered to be of Pliocene age (David, 1945, p. 315—318). Flora of fossil plants found in lower Peace Valley Beds in Piru gorge few miles south of mapped area considered to be of middle Plio- cene (Hemphillian) age (Axelrod, 1950, p. 159—214). HUNGRY VALLEY FORMATION or CROWELL (1950) A fluviatile sedimentary sequence of late Pliocene age overlying Peace Valley beds in hills between Peace Valley and Frazier Mountain and southwest of San Andreas fault. Named, described, and mapped in detail by Crowell (1950, p. 1633—1637, fig. 4; 1952, p. 14—16, pl. 1). Weakly consolidated gray-white arkosic sandstone and pebble-cobble conglomerate; some interbedded light-red to greenish-gray sandy siltstone. Cl-asts of conglomerate mainly of granitic rocks, some of meta- morphic rocks, others of Tertiary andesitic and felsitic volcanic rocks. Formation about 4,000 feet thick; top eroded. Vertebrate fossils found 600 feet above base of , Hungry Valley Formation include teeth of large horse R, H W. R l2 W. TERTIARY SEDIMENTARY AND VOLCANIC ROCKS z <— w 4 E AHVILEEL'EHd /——/% 3 E E E 3 x S X m s: E o a .c: ; e 61 ,2 o N O u a 3 z 33 ‘= s a = :2 E ‘3’ m E: Z/IK. o AHVNEELVDO AHVILHEJ. 3 q: o a 2% a: g 0 § g S 3 m 2 2 a a n O m an .E E 3 3 3 8 z '4 g t .g :1 g .3 a t -<'§ o ‘H s u m . g c. a g = — «I 9‘ E - m a E I! 3 '— 8 3 . .2 93 E .2 < z 2*: . s E f: z a Z 8 E E x x o g .x < z m o ' E :1 ° 2 E _l 3 3 >, >. .H "3 :1 g. o. E .2 E g E g i 5 “5 >< E E E O m E m N 2 22 T: U E‘ ~3 umymna (Ae_|_)u0l19u1.10d (gq duaoguuuod JGPIO apmwv (2.) [M'Jq‘lwnd 1749993 914290;st yuammg macaw 4‘!an SVEHONV NVS 239—655 0—67 5 FIGURE 34.——Geologic map and sections of Palmdale area (modified after Wallace, 1949, and Noble, 1953). 57 58 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Pliohippus or Plesippus; considered either late middle Pliocene (late Hemphillian) or early upper Pliocene (late Blancan) age by Chester Stock (in Crowell, 1950, p. 1638) ; overlying beds of formation considered to be upper Pliocene. WEST ANTELOPE VALLEY AREA NEENAOH VOLCANIG FORMATION A volcanic sequence of Oligocene( ?) and Miocene age unconformable on pre-Tertiary granitoid rocks and overlain by sedimentary rocks of late Miocene age. In hills west of Antelope Valley, northeast of San Andreas fault, exposed as a narrow strip adjacent to this fault near Gorman, and from La Liebre ranch southeast to Pine Canyon (figs. 35—37). Formation hereby named for a former school in Neenach quad- rangle. Type section exposed in large canyon about a mile east of La Liebre ranch (projected 81/; sec. 14, sec. 23, T. 8 N., R. 17 W., San Bernardino meridian) in which all facies are present (fig. 36). Andesite and felsite two major recognizable facies; minor exposures of perlite, tufl' breccia, and bentonite; rare thin lenses of conglomerate, sandstone, and lime- stone reported by Wiese (1950, p. 31). Andesite flows dark reddish to purplish brown, aphanitic to slightly porphyritic, massive; some flows slightly vesicular, rarely scoriaceous. Thin sections show rock to be mass of plagioclase (calcic andesine) laths intermixed with iron oxides; most of phenocrysts are biotite largely replaced by hematite, chlorite, and epidote (Crowell, 1952, p. 11). Felsite light colored, greenish gray, pink, red, brown to tan, flow banded to massive, aphanitic, very hard, siliceous; presumably in range of composition from rhyolite to dacite. Perlite greenish gray to steel gray, massive to flow banded, vitreous, brittle; innumerable curved frac- tures; perlite-to-felsite transition rock contains spher- ulites; cavities and fissures filled with opal or chal- cedony. Tufl‘ breccia cream white, massive, indurated, com- posed of angular fragments of felsite in fine-grained partly silicified tufl’aceous matrix. Andesite and felsite in part contemporaneous, ande- site in part younger; perlite locally forms basal chilled facies of felsite; tufl' breccia forms base of formation in type section and in Pine Canyon; small lens of fel- site agglomerate at top. ' Neenach Volcanic Formation pre-late Miocene in age. Considered possibly Oligocene, and early or middle Miocene, as suggested by its similarity to, and possible correlation with, andesitic and felsitic rocks of Vasquez Formation (Sharp, 1935) south of Sierra Pelona, Kinnick Formation (middle Miocene) in Tehachapi area, and Tecuya Beds (Oligocene or Mio- cene) of Stock (1920; 1932) and Vaqueros Formation as used by Hoots (1930) in southeastern San Joaquin Valley, all known to be of that age range. QUAIL LAKE FORMATION A marine and brackish-water sedimentary sequence of shale, sandstone, and conglomerate of late Miocene age exposed at west end of Antelope Valley; referred to Santa Margarita Formation by Wiese (1950, pl. 1, p. 32-53) and Crowell (1952, pl. 1, p. 12—13). Un- conformable on Neenach Volcanic Formation and Mesozoic granite; gradational upward and laterally northeastward into fluviatile beds of Oso Canyon For- mation. Exposed northeast of San Andreas fault, in hills northwest of Quail Lake, also in hills to south- east near La Liebre Ranch (pl. 1). Formation herein named for Quail Lake; type sec- tion exposed from point 21/; miles N. 60 W. of center of Quail Lake eastward down ridge for 11/2 miles (fig. 35). Lower part of formation mostly shale that grades laterally northeastward into sandstone; conglomerate at base; upper part nearly all sandstone. Shale dark brown to nearly black; bleaches light brown on weathering; thin bedded, micaceous; ranges from ellipsoidal—fracturing clay shale to harder platy- fracturing semisiliceous shale; southeast of Quail Lake, shale light colored, porcelaneous, probably tufl'aceous. Sandstone gray white; weathers bufl'; moderately hard, massive to bedded, medium to coarse grained, commonly conglomeratic, arkosic. Conglomerate com- posed of rounded cobbles and pebbles of granitic rocks and pink to white (bleached) rhyol-ite in matrix of coarse arkosic sandstone. Sequence of type section as follows in descending order: Quail Lake Formation exposed at type locality 2V2—1% miles west- northwest of Quail Lake Sandstone; contains shell fragments in a few places. Grades eastward, northward, and upward into terres- Em. trial red and green sandstone, siltstone, and fanglom-mmfl” erate of Oso Canyon Formation; downward through (feet) interbeds into shale _____________________________ '-_ 1, 000 Shale; contains several thin beds as much as 5 feet thick of sandstone, which increase in abundance as shale grades northward into sandstone ____________________ 1, 300 Sandstone and conglomerate; contain scattered pebbles and cobbles that increase in abundance and size as sandstone grades downward into basal boulder con- glomerate of granitic detritus; clasts of purple-brown andesite where this formation rests unconformably on Neenach andesite _________________________________ 250 Total thickness, Quail Lake Formation __________ 2, 550 59 TERTIARY SEDIMENTARY AND VOLCANIC ROCKS .wv - Vm SR: 5320 ES 58H 55;» SE 3583 3:5, 323.8 no 25 H83 £93 gong 958% S can 55:5 85 .833 ya 32: 3m28¢|fim ".3an AHVILHEL AHVILHEL‘EHd AHVNHELVDO r—H i- Cm Act 5:5.5: ciao—ox» £05502 23x35 «:3 wind—.5 Act—SEE: Lab wand :35 Awfiuryiuv Act—552: Lek 5555 30 A SEE—5: V 3:833: 05: 3—002 AEV wind: - «£4: \\ \ — \ a >tlk0k200>3 . £55 38?. 332 $54 7 A A £393.. A 4 v >L===< ZO_.—.< ‘ v n 7 av A l>_ v >9 p 4 a: A» vyi’ W" ‘1 4; vg v“ n 4 1: AD» v v \y b A47, DA . q v 4 I? . 4v <1 03 ' .(x \, m s \ _ ' "'umli" 4 , \ \ , ’«,'/‘\ \ ., M 34-44' EXPLANATION >. 8 § 1 . E \) Alluvmm (Qa) Z a II c. . m g g Older allnvmm (Qoa) l; E g :1 O LINCONFORMITY ' Oso Canyon Formation (To) 0 V2 1 MILE a |—___.l_._____l E Quail Lake Formation (Tq) 'E UNCONFORMITV >. E II a s O . l- x'. Andean/e ,3 A II : c L” E s: F 3 Felsite "o‘ UNCONFORMITV >- 3 > 5 n: ‘ .5: 5 s - I , -< O Perlite 3 a J \\ .1", Quartz monzonite (qrn) E; I: E - / ,~ \ 0.0: 8 g L|J L Tuff breccia Z '— FIGURE 36.—Geologic map of Cow Springs Canyon and Pine Canyon area, west end of Antelope Valley (in part modified after Wiese, 1950.) In area west of La Liebre ranch, formation attains rita Formation (upper Miocene) of southern San Joa- maximum thickness of 2,700 feet. Section exposed quin Valley as mapped by Hoots (1930, pl. 1) ; on this here strikingly similar to that of type section north- basis, Quail Lake beds correlated with and referred to west of Quail Lake (figs. 36, 37) but lacks marine that formation by Wiese (1950, P- 33a PI- 1) and Crowell (1952, p. 12—13, pl. 1). fossils. Marine molluscan and echinoid fossils from beds 080 CANYON FORMATION mapped as Quail Lake Formation in Oso Canyon and A coarse fluvi-atile sedimentary sequence of late vicinity include four Species present in Santa Marga- Miocene age exposed at west end of Antelope Valley; 61 TERTIARY SEDIMENTARY AN'D VOLCANIC ROCKS .3 and mm mean no Epcnm 93 no? no gouaoou .558» 3282 no 65 $95 as 2:: no mnouoamlsm BEER _|'1‘|J|_ mtg; « W» O 4m>m4m4 (mm .8ON Ju>uu_ (ww boom __ r\».~¢ w H V 4 ~m~ VI 4| ‘ a . ~r. 1‘ _, _. ~ 1‘ I v u~ I ‘u t o ~ § n _. ‘ utu .‘ .~ 0 l ‘ ¢~9~Ja \;\Itlsu¢:\ul~:\k sv~.-m=4~a..l.l. \ n . 4m>wn_ (mm 117.5 . ‘ 11—. ~o~ \-Is “o~¢ boom no u n ..|\\nv’li\ 500v 62 mapped by Wiese (1950, pl. 1) as continental deposits, Miocene( t), and Santa Margarita Formation. Lower part gradation-a1 southwestward and downward into Quail Lake Formation; northeastward becomes un- conformable on Neenach Volcanic Formation and on Mesozoic granite; unconformably overlain by Meeke Mine Formation. Formation herein named for Oso Canyon; type sec- tion exposed from contact with bufi' sandstone of Quail Lake Formation two-thirds of a mile north of west end of Quail Lake along line N. 20° E. for 2 miles, across Oso Canyon to contact with overlying Meeke Mine Formation (fig. 35). Formation about 5,500 feet in maximum thickness; composed of interbeds and intergradations of fanglom- crate, conglomerate, sandstone, and siltstone. Fan- glomerate composed of unsorted subrounded clasts ranging from pebbles to boulders in matrix of gray— white friable coarse arkosic sandstone. Conglomerate similar but clasts are moderately sorted pebbles and cobbles. Sandstone buff white to red, friable, fine to coarse grained, commonly gritty or conglomeratic, arkosic. Siltstone greenish gray to red, soft, mica- ceous, argillaceous to sandy, commonly pebbly. Fan- glomerate massive, other sediments bedded, commonly crossbedded and with filled stream channels. Forma- tion composed mainly of detritus of granitic rocks, including pegmatite, aplite, and abundant fragments of bleached white massive to flow-banded rhyolite identical to that of Neenach Volcanic Formation. Oso Canyon Formation same age as Quail Lake Formation (late Miocene) into which it grades later- ally. MEEKE MINE FORMATION Sequence of fluviatile gravel and lacustrine clay of probable late Pliocene or early Pleistocene age exposed discontinuously in southeastern foothills of Tehachapi Mountains from Oso Canyon northeastward 8 miles to Antelope Canyon (pl. 1; fig. 35). Mapped as Plio- cene( ?) lake deposits by Wiese (1950, p. 35—36, pl. 1). Unconformable on Oso Canyon Formation and pre- Tertiary rocks; about 1,500 feet thick; unconformably overlain by older alluvium. Formation named for nearby Meeke tin mine. Type section that exposed from contact with Oso Canyon Formation 21/2 miles north of west end of Quail Lake northeast 1 mile to Kern-Los Angeles County boundary (fig. 35). AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Formation consists of two units of gravel separated by one of clay and clay shale. Sequence as follows: Meeke Mine Formation exposed from 1 to 4 miles northeast of 080 Canyon, including type section (fig. 36) Older alluvium (Pleistocene). - E timat d Unconform1ty. . £50k“; Meeke Mme Format1on: (feet) Gravel, weakly consolidated; no discernible bedding; composed of subangular to rounded pebbles and cobbles of granitic rocks, hornfels, black schist, quartzite, and marble in matrix of gray— —brown loamy gritty sand _____________________________ Clay shale, light gray to tan, less commonly pink thin bedded, soft to moderately hard, somewhat siliceous or possibly tufl'aceous; contains occasional layers few inches thick of impure limestone and soft buff fine-grained sandstone _________________ Clay, gray, soft, crumbly when dry; no discernible bedding; exposed only in gullies ________________ Gravel, similar to gravel at top of sequence, but in southwestern exposures bedding barely distinguish- able through residual soil; in northwestern expo- sures includes several lenses as thick as 6 ft of conglomeratic marl or limestone ________________ 150 400 150 800 Total estimated thickness, Meeke Mine Forma- tion _____________________________________ Unconformity. Oso Canyon Formation. 1, 500 Weakly to moderately consolidated sedimentary rocks near Antelope Canyon (fig. 11) about 1,650 feet thick questionably assigned to Meeke Mine Formation; composed of gray-white arkosic sandstone and con- glomerate and a tongue of clay shale as thick as 250 feet. Conglomerate clasts mostly of granitic rocks; abundant clasts of marble and hornfels in lower part. Smooth—shelled ostracods in shale and concretionary aggregates of calcareous algae(?) in basal limestone lens 1 mile southwest of Meeke mine indicative of fresh-water environment but not of age. Great angular discordance with underlying upper Miocene formations suggests Meeke Mine Formation is Pliocene or younger, most probably upper Pliocene, possibly early Pleistocene. ROCK UNITS OF CENTRAL AREAS Nearly all of Tertiary rocks of central areas mapped as Tropico Group (Dibblee, 19580, p. 136—138), a sequence of nonmarine sedimentary, pyroclastic, and volcanic rocks unconformable on pre-Tertiary crystal- line rocks and unconformably overlain by Quater- nary alluvial sediments in Antelope Buttes, Little Buttes, Rosamond Hills, Middle Buttes, Soledad Moun- tain, Bissell Hills, Castle Butte area, Kramer borate area, Kramer Hills, and Red Buttes (pl. 1). Maxi- mum exposed thickness about 2,800 feet. Assemblage characterized by rapid lateral changes in lithology. TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 63 Type section within half a mile west of Mojave- Tropico road in western Rosamond Hills 1—2 miles north of Tropico mine, or NElfll sec. 2, T. 9 N., R. 13 W. (Dibblee,1958c,p. 136) . Tropico Group divided into units as shown on table 1. ANTELOPE Bum ROSAMOND, AND MOJAVE AREAS GEM mu. ronnuron A dominantly pyroclastic sequence of silicic tulf, tufl' breccia, and tufl‘aceous sandstone in Antelope and Little Buttes, Rosamond Hills, Middle Buttes, Soledad Mountain, and eastward to Bissell Hills (pl. 1); un- conformable on Mesozoic quartz monzonite; includes associated silicic extrusive and intrusive volcanic rocks of Bobtail Quartz Latite Member. Named and de- scribed by Dibblee (19580, p. 140; 1.963, 164—187) ; type section at Gem Hill in western Rosamond Hills, 51/2 miles northwest of Rosamond, or 81/2 sec. 25, SE14 sec. 26, and NEIA sec. 35, T. 10 N., R. 13 W. Gem Hill Formation rests on red-weathered undulat- ing surface of quartz monzonite. At Antelope Buttes, formation about 1,250 feet thick, composed of white bedded lithic tufl", tufl' breccia and tufiaceous sandstone, and a lens of weathered basalt as thick as 20 feet (fig. 38). At Little Buttes about 800 feet of tufi‘aceous strata and some carbonate interbeds exposed. At Gem Hill in Rosamond Hills, Gem Hill Forma- tion about 1,290 feet thick (Dibblee, 1963, p. 168—169) ; thins eastward; composed of white to greenish-tan lithic tufl', tufl'aceous sandstone, tufi' breccia, and con- glomerate of quartz latite detritus; also several thin basalt flows (figs. 39, 4-0). Tufi' of Gem Hill Formation composed of devitrified glass shards, grains of feldspar and quartz, flakes of biotite, devitrified pumice lapilli, and fragments of tan and pink to brown rhyolite or quartz latite felsite and porphyry. BOBTAIL QUARTZ LATITE MEMBER Member consists of felsitic and porphyritic volcanic rocks of quartz latite or rhyolitic composition occur- ring as plugs, pods, and dikes intruded through pre- Tertiary granitic rocks into stratified pyroclastic rocks of Gem Hill Formation and as short lenses of flow breccia within that formation in vicinities of Rosa- mond Hills, Middle Buttes, Soledad Mountain, and eastward to Bissell Hills (pl. 1) ; named after Bobtail mines, Soledad Mountain (Dibblee, 1958a, p. 140—141; 1963, p. 178—184); type locality, Soledad Mountain (secs. 6 and 7, T. 10 N., R. 12 W.). Four facies of Bobtail Quartz Latite Member recog- nized and mapped (figs. 39—42) as follows: porphyry, felsite and porphyritic felsite, and perlite, all of in- trusive origin, and felsite breccia, of probable extrusive origin. Porphyry massive to faintly flow laminated, pink to brown; composed of phenocrysts of plagioclase (Oligo— clase), orthoclase (sanidine), quartz, hexagonal plates of hematite (after biotite?), and elongated black vugs (after hornblende?) in aphanitic groundmass (index of refraction 1.53) with disseminated hematite; pheno- crysts make up 25—30 percent of rock. Forms large plug east of Soledad Mountain (fig. 42) and several dikes on Tropico Hill (fig. 39) . TABLE l—Divtsions of Tropico Group in western Mojave Desert and their presumed correlations [See pl. 43 (or thickness and lithology of divisions] Rosamond Hills 8' 11 Castle Kramer East Kramer Kr Age and Antelope I??? Butte borate borate Hillamer Buttes areas 1 s area district district 8 area 0 Fiss Bissell Upper part Upper part Upper part 5 Fanglomerate Formation .§ 9 > E g Saddleback / Red Buttes E '8 5 Basalt Quartz Basalt _ as o l- 8 Q 8 Gem Hill \ Gem Hill g Formation* Formation Lower part Lower part Lower part Lower part *Includes Bobtail Quartz Latite Member in Rosamond Hills area 64 AREAL GEOLOGY, WESTERN MOJ AVE DE SE RT, CALIFORNIA R‘s W. R. 14 W. '7 . . EXPLANATlON <9 .../ 2/ 20 g E .. Alluvium E .~/ \ § >Lu ' . x7, w L; ,‘/ / \ § 3 . ‘ up "’ 3 o /,’H’/\\ Older alluvium a \ ' ’ ‘ _.I/‘<,‘ :Zéf/g/ UNCONFORMITY 1/' II \,\ \,\,\/ "I‘\'l/:l>‘\l‘( g 00 :\ \J \— ’/\ '._\/—/\ 5'3 0 o o T —/\_ 1 ///_\'/\\j BE I ' o . \I\ I/ I / \ \/z\ ‘ i: 2 Fanglomerate Felsite breccia Fanglomerate 3- 3 K 0 o o o o . /\ /\ -/ m . . , V 25 . >__° . /\ _ t I / c of volcanic of granitic 9 N. . o o 030 , \ z /I _-\ on g ‘ ‘ ' ° .00 ‘ :/\/\/'\’\~/// \ (:I,’ a. h detritus detritus § . . ' °o a °50 \/>\:1/\77\ / /’_/ g 'e >- . / \l — / l h UNCONFORM/TY E 0: ' / \— / :\ 0 OK! / /\ /\ \ / \ U 8 < - 0° 0 ZOOAnt -’\Buttes/\-*YAI o >; o 0° '// \‘I/l‘l /\ .0 K 00 - 2oo°°° O°O°°p \~\f/‘\)\/\’*\/\//\ E.‘ ‘t E . -\° I \ \(lrlj mg Basalt a gs : Tuff UNCONFORM/TY E < ‘ r77\ 1 I: \ / \// /\ \ E] . f»— Quartz monzomte “'1 O: [1. SEA LEVEL SEA LEVEL FIGURE 38.—Geologic map and sections of Antelope Buttes area. Felsite and porphyritic felsite pink, red, brown to grayish green, tan to cream white, aphanitic to sub- vitreous, some containing phenocrysts that compose as much as 20 percent of rock of same minerals as those of porphyry facies. Most widespread facies of Bobtail Quartz Latite Member; similar to felsite of Neenach Volcanic Formation. Perlite steel gray, vitreous; numerous curved frac- tures; forms chilled marginal border facies of some intrusive bodies of felsite and porphyritic felsite in Rosamond Hills and Soledad Mountain (figs. 40, 42). Felsite breccia forms one extrusive and partly in- trusive lenticular greenish-tan mass 1 mile south and southeast of Soledad Mountain (fig. 42), and another composed of brecciated dark-red fielsite in Rosamond Hills 1 mile north and northwest of Rosamond (fig. 40). Willow Springs Mountain and Tropico Hill each composed of pods and merging dikes of pink to bufl' felsite of Bobtail Quartz Latite Member that trend east and dip steeply south; intrusive into quartz mon- zonite and basal tuff and tuff breccia of Gem Hill For- mation (fig. 39). Middle Buttes composed of several pods and masses of bufl' felsite of Bobtail Quartz Latite Member elongated northwesterly, intrusive into quartz monzo- nite and overlying tufl'aceous rocks of Gem Hill For- mation (fig. 41); tufl'aceous rock so hydrothermally altered as to be almost indistinguishable from intrusive quartz latite. Soledad Mountain composed of several large pods of pink and green to buff felsite and porphyry of Bob- tail Quartz Latite Member intrusive into pyroclastic rocks of Gem Hill Formation and underlying pre- Tertiary rocks. Porphyry and felsite massive to flow laminated; flow laminae and fracture partings of each intrusion parallel to outer margins; porphyry intruded by felsite and therefore older (fig. 42). About 1,000 feet of Gem Hill Formation here exposed; composed TERTIARY SEDIMENTARY AND VOLCANIC ROCKS R. 13 W. Willow Springs Mountain 16 In. 00.. coo-cocooooooO-IO 15 o-oohoooocnooooono coo. oucuuoOoO~o 00.00.... 13 SEA LEVEL SEA LEVEL FIGURE 39.—Geologic map and sections of Willow Springs Mountain, Tropico Hill, and Western Rosamond Hills. Explanation on figure 40. AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA .zwa - ‘ _‘ / ~_ / \ \ ‘\ ‘; I \ \\— ,\— 0-11 by; \”/'\”\\ /\\'> :\‘\ K " /— \‘,‘\ \‘/\\ \ ‘\\‘l\/\\\\\’\\/i\l\/\/\\ - —— / ”//\ ‘\ /\ /! \\ ‘ ,\///~) \ \ \ l\ \\\ \‘I, /~. \ l/ \3\/\\/\ \\\/2/1/\/f\\ : / “\/ \\ l/\://\‘_\\\\/\/. ,4 EM /Hil|5\/\;‘\l// \\\‘\\\/w\/ //‘ \\7 /LL”‘ —\‘ ‘4\:fll\ / .' \\\ \:\\\,\ \/’\_//\‘/ / ‘\’/\ /_\\\’\/\’;'\/.\j/\\/\\\\\\\\\ \\\\ / \ 1 / /— If \ / \\ / \ ‘./ // \ /\\\l\\\\\/\||\\/\‘ \/\1‘/ / /‘ //\/l___\ //\\\\\\\\~.\’/ _ /‘//\\\\\ ‘ <\"\\\I: /\/1/\\/\/ A“ ' \\ ’\ \\ /_/’.—\/I\ \ /\\%1\\\/\\\\ /: 1‘2 / <\\\ \/\/’\‘/-\l/\\/‘/’\ «I: . \/ ”\/ \\ -—_//\//\ /. /l./\/, ‘r /— — qm//\ _.\_/ l ' 25.. \\’/l\\l//l\'/f/\ ( . ///\;// (\l/\ /1/ Ir“ / / //\; I / !/\\‘ /// \\\\L A?“ 11¢, \~ ; 5212/ mi“ . ~.\/ \. " .-".'.'.... . /\/ ”nun-1'0“". \" \ o 7’3 / 17 \ 13 "'.>.-......:u. 0...”. i , ......... RedHHI It] Rosamond N 0 vs 1 MILE \—._J—_J I EXPLANATION C C - 2000’ Alluvium and windblown sand fi LE Z _ UNCONFOPMITY 5' § E] U < 8 :> SEA LEVEL g 0 Older alluvium “- , 3 UNCDNFORMITV D D e . \ / {£2 ’ F 2000, g Fanglomerate a: ’ h LOCAL UNCONFORMITV § ._ I. >_ a. {2'3 I .§ 0: 5 a E r/ E < SEALEVELE g 8’; E >3 >E .g .3 g 3 Pei-lite Porphyry Felsxte and ‘3 Lu a 6E! .g E breccia porphyritic § F E 3 mg . felsibe g E El :2 m ginesl indlicate tigersd ())f as P ‘ w“ ow ammae an or T E M fracture parting) ._ w Tuff and Basalt - l/ ‘/ - "2000' U tuff breccia ‘7\ 7‘41"“ \ \ / I *\\/\ \/\:| \/\\:\\:\\7\ 7\\::\//\ \:\ \:\\: /\:’ UNCONFORMITY / / / wan / \ \\/\\/\\/\\/\\/\ \\/\ \fi\\’\\/ SEA LEVEL m Pegmatite dikes —— //\ Quartz monmnite FIGURE 40,—Geologic map and sections of south-central Rosamond Hills. V PRE-TERTIARY TERTIARY SEDIMENTARY AND VOLCANIC ROCKS R.13 W. CACTUS QUEEN MINE 14 13 (2 am“ “if” [Z703 19 ® A I Recent Oligocem (?) to middle Miocene (2) 67 EXPLANATION > E < Z R u Alluvium and windblown sand t; : _ _ ~ 0 El — :1 __'=7: Felsite and porphyritic Bobtail Quartz felsite (lines Latite Member >- _ indicate trend E J ‘ Gem H.111 of flow laminae I: Formation and fracture n: ' m parting) |_ ‘§\l:\ \ 1 V. k Tuff breccia >_ [I < l\ qrn F: /\ & UJ . J +— Quartz monzomte “:1 [E D. 0 V2 1 MILE ;_;__l SEA LEVEL FIGURE 41.—Geologic map and section of Middle Buttes. of greenish-white lithic tuif breccia, tufl'aceous sand- stone, felsite conglomerate, and basalt. Gem Hill Formation unfossiliferous but similar in lithology and in stratigraphic position to Neenach, Kin- nick and Pickhandle Formations and possibly to Vas- quez Formation. Age may therefore be Oligocene to middle Miocene, but closer age assignment not possible. PISS FANGLOMERATE Coarse fanglomerate overlying Gem Hill Formation in Antelope Buttes and in Rosamond Hills; named after Fiss Hill in western Rosamond Hills (Dibblee, 1958c, p. 141), described previously in detail (Dibblee, 1963, p. 187—191). Type section at Fiss Hill, 11/2 miles east of north of Tropico mines (sec. 1, T. 9 N ., R. 13 W.). Fiss Fanglomerate reddish brown, crudely bedded; composed of boulders, cobbles, and pebbles of felsitic and porphyritic rocks derived from Bobtail Quartz Latite Member, and few of granitic rocks; includes several small masses of brecciated felsite. At Gem Hill, fanglomerate about 900 feet and grada- tional into underlying Gem Hill Formation; about 500 feet exposed at Fiss Hill; about 300 feet in foothills northeast of Rosamond and unconformable on Gem Hill Formation. About 1,700 feet exposed at Antelope Buttes. Formation unfossiliferous, but presumably of Mio- cene age, probably correlative with lower part of 050 Canyon Formation as suggested by similarity in lithol- ogy and stratigraphic position, as well as to coarse alluvial facies of Bopesta Formation in Tehachapi area, Barstow Formation in Gravel and Mud Hills, and Punchbowl Formation south of Palmdale, all partly or entirely of Miocene age. BISSELL FORMATION A fluviatile and lacustrine sedimentary sequence overlying Gem Hill Formation in Bissell Hills (fig. 43) after which formation was named (Dibblee, 1958c, p. 141—142; 1963, p. 191). Type section exposed from 68 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA RIZW, 5a EXPLANATION - ’i’!‘ 6: § { W 0 Ft 3% << Alluvium 82 \H EXPOSED TREASURE AND \ UNCONFORM/TV DESERT QUEEN ~11st ,—-.~ ‘2‘ u \ \Q } '§ g x ‘\\ .1 Q a: Felsite and Porphyry Perlite E E porphyritic < 33 34 Q .g felsite ,2 § ‘4 I: g .3 (lines indicate trend {'5 T- .E g g of flow laminae ‘ 1NI E a g and (or) fracture ' g E 0' parting) . o = E k‘ 5 V VA ‘ II; = E ‘8 Mm $21" ¢ 4 N w :3: m _ . a Felsite breccia EEACé-ligflzcgs MINES 0 6¢ v I V E 0 / § 8 >- "¢ 1 ¢ 3 mumnurmu E § (\HuuHH/ml ; 3 ° Basalt E ,_ \, Tufv‘f.an'd' tuff UNCONFOPMITV breCCIa Pegmatite dikes E It ‘ s 12 10 L\_/ \ / E E _ = Quartz *7 w . m D monzomte a: “A A54 gay “ -- ”V“ ._ , . o 4; - \mum Metaquartz \\\ . ' - “WWW ® a5 lame ',\\ -‘ ’ Wing/1’7“” ' \\ “3% ' m ’ g .1 . o . \ ‘ . 3 0. GD, . \ ’ 12 17 j 15 15 .,o “0' o... 3 Gloster "'0 C . C o o". \ '. A A, _ V m o 1k 1 MWLE ~ Soledad Mountain L————-—'———’ 4000- . I -4000' _ '00. - , -"‘/1// - l H‘ j J -' “Ut\ \//'\\,\\ \H\ ‘ , 1-“ \l‘ lJ\/\\,,_ 2000'- \\[HH [H /,\ a“ ‘\I‘ll‘ /\’/\//\\\l .2000, 4m!) 1177/ N l"1n“‘3n‘-// \/ \/I/ I J V f. E / a Magnesnte ints SEA LEVEL ‘ Sandstone member 3.‘ Claystone member 9 l g i Carbonate and ‘7 o. shale member g s >- E . DC '8 U Bissell Formation 4: § 3 _ I: s: '5 Bobtail Quartz Latite E, § 5 Member (intrusive) I— § 1- "if-I Tuff and basal g conglomerate o . : Basalt i Gem Hill Formation UNCONFORMITY SEA LEVEL >. _ / . B: In t ’ El; 0 V2 Quartz monzonite J Lu gFA—g ,_ FIGURE 43,—Geologic map and section of Bissell Hills area. 7O AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Carbonate and chert strata are as much as several feet thick; occur in shale. Carbonate strata, yellow- ish-gray to nearly white, very hard, bedded, aphanitic; range from limestone to dolomite in composition; some layers have nodules of gray chert Chert layers, trans- lucent gray to nearly black, locally mottled with brown, green, yellow, red; very hard but brittle and closely fractured; range from opal to impure chalce- dony in composition. Shale is tufl'aceous, siliceous, or clayey; tufiaceous shale nearly white, soft, thin bedded to massive; sili- ceous shale, cream white, hard, platy, coarsely lami- nated, slightly to moderately procellaneous; clay shale gray, rarely green or red, soft, crumbly, argillaceous to silty, micaceous. Sandstone light gray to buff, friable to locally mod- erately hard, bedded, fine to coarse grained, arkosic, commonly micaceous. Conglomerate, composed of pebbles, cob‘bles, or boulders in matrix of arkosic sand- stone; clasts mostly of granitic rocks, locally of dio- rite, quartzite, and metavolcanic detritus. Breccia com- posed of granitic detritus, locally of dioritic material. Basalt black, weakly coherent, massive; of fine- to medium-grained diabasic (ophitic) texture; locally slightly amygdaloidal; composed of 40—50 percent plagioclase (labradorite), 25—30 percent augite, 10—15 percent olivine (partly altered to iddingsite and antig- orite?), 1—4 percent magnetite and ilmenite, small amounts of secondary minerals (chlorite, hematite, limonite, calcite, chalcedony). Lower part of Tropico Group exposed nearly 2,000 feet thick; sequence chacterized by rapid lateral changes of thickness and lithology, but lowest beds mostly pyroclastic, upper beds mostly sedimentary. Lower part of Tropico Group prominently exposed in Castle Butte area (fig. 44) as follows in descending order: Lower part of Tropico Group (sec. 26 and N}é sec. 35, T. 82 S., R. 38 E.) Fanglomerate. Unconformity. Thickm" Lower part of Tropico Group: (feet) Basalt _______________________________________ 50¢ Sandstone, hard, thick—bedded, coarse-grained, gritty; contains minor thin layers of sandy shale; forms prominent hill ________________________ 200 Clay shale, gray; contains few hard platy layers as thick as 2 in. ; also a 5—ft-thick layer of sandstone 105 it below top ____________________________ 260 Siliceous shale; uppermost 3 ft composed of hard ledge-forming dark chalcedonic chert and oc- casional limestone beds ______________________ 50 Lower part of Tropico Group (sec. 26‘ and N% sec. 35 T. 32 8., R. 38 E.)—Continued Thickness Lower part of Tropico Group—Continued (feet) Tuff _________________________________________ 20 Basalt; lenses out to west and east .............. 0—20 Sandstone, medium-grained, tufl’aceous __________ 13 Tufi _________________________________________ 260 Sandstone, coarse-grained, gritty; lenses out to east _______________________________________ 0—30 Tufl' _________________________________________ 100 Tuif breccia __________________________________ 7O Tuffaceous shale, siliceous shale, and clay shale, interbedded; tufiaceous shale predominating- _- 45 Basalt; lenses out to east and west ______________ 0—15 Tufi breccia __________________________________ 10 Siliceous shale ________________________________ 25 Tufi breccia and minor interbedded tufi _________ 117 Andesite breccia, green to reddish-brown, unstrati- fled; lenses out to west ______________________ 0—190 Total thickness exposed (exclusive of two lower basalt lenses) _____________________ 1, 440 Unconformity. Quartz monzonite. Pyroclastic lower unit exposed nearly 10 miles east- northeast of Castle Butte (fig. 45), with sequence as follows: Lower part of Tropico Group (SWM sec. 5 and SE% sec. 6‘, T. 39 S., R. 40 E.) Quaternary older alluvium. Unconformity. Lower part of Tropico Group: “’0’“ ”£88 Lithic tufl’ breccia, thick-bedded, greenish-yellowish- (fed) white _______________________________________ 200 Fanglomerate of quartz monzonite boulders as much as 2 ft in diameter ____________________________ 30 Quartz latite, mafic, gray, fine-grained, massive _____ 5 Bentonite and tuff ______________________________ 30 Total thickness exposed _______________________ 265 Unconformity. Quartz monzonite. In areas between Castle Butte and Saddleback Moun- tain, and in Muroc and Stonehouse Hills northwest of Boron, lower part of Tropico Group (referred to Rosa- mond Series of former usage, by Gale, 1946, p. 350— 357, pl. 52) ranges from 100 to about 1,200 feet in thickness; composed of lithologic units as shown on figures 45—48. In low hill just south of Kramer borate mines (fig. 46), about 200 feet of exposed strata, presumably of TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 71 lower part of Tropico Group, are as follows in descend- ing order: Lower part of Tropico Group (SEX sec. 23, SW% sec. 94, T. 11 N ., R. 8 W.) Quaternary(?) granitic cobble-boulder conglomerate. Unconformity. Lower part of Tropico Group: 723: Tufl'aceous shale; contains a few limestone beds as (feel) much as 1 ft thick ____________________________ 104 Limestone, cherty, in beds as much as 5 ft thick; interbedded tufi‘aceous shale ____________________ 37 Arkosic sandstone _______________________________ 13 Basalt _________________________________________ 6 Tail and bentonite ______________________________ 40 Arkosic sandstone, coarse-grained _________________ 0—10 Total thickness exposed _______________________ 210 Unconformity. Quartz monzonite. In large alluviated area north of Kramer Junction (or Four Corners), gray coarse granitic cobble con— glomerate and breccia presumably of lower part of Tropico Group exposed at only one place, just west of U.S. Highway 395, 4 miles north of Kramer Junction (fig. 49) ; similar conglomerate penetrated in three core holes to south drilled for U.S. Geological Survey; deepest penetration of 1,650 feet into conglomerate by hole 4 (fig. 49, sections; table 3). In Kramer Hills and vicinity, lower part of Tropico Group ranges from about 500 to 2,000 feet in exposed thickness; overlain by shale of upper part of Tropico Group, or unconformably by Red Buttes Quartz Basalt (figs. 50, 51) ; five lithologic members recognizable in various parts of Kramer Hills (Dibblee, 1960d, p. 90—96), as follows in descending order: Member 5. Clay shale, locally tuffaceous. 4. Carbonate rocks and interbedded shale. 3. Sandstone and shale, including lens of granitic breccia. 2. Carbonate rocks and interbedded shale. 1. Tufl’, sandstone, and conglomerate. Flows of basalt present in members 1, 3, 4, and 5 and lens of dacite vitrophyre in member 1 (fig. 50). Exposed sequences of lower part of Tropico Group in various parts of Kramer Hills disconformably or unconformably overlain by Red Buttes Quartz Basalt; unconformably overlie pre-Tertiary quartz monzonite or metamorphic rocks. descending order: Sequences as follows in Lower part of Tropico Group exposed in northern part of Kramer Hills just east of U.S. Highway 395 (secs. 33 and 34, T. 10 N., R. 6 W.) Thickness Member (feet) 5. Clay shale; contains 2 beds (5—10 ft thick) of dolomite _________________________________ 905: Basalt; contains 2 beds (5—10 ft thick) of dolo- mite _____________________________________ 562 Clay shale; contains 3 layers (5—13 ft thick) of thin-bedded dolomite and shale; includes 2 tongues of basalt that wedge in from north__ 212 4. Dolomite; interbedded siliceous shale and some chert ____________________________________ 25 3. Clay shale; at least 5 ft of basalt near middle (member largely concealed) _________________ 225 2. Dolomite and interbedded tufl'aceous shale, rare chert ____________________________________ 86 1. Tufi _______________________________________ 168 Sandstone, gritty, arkosic ____________________ 45 Basalt _____________________________________ 45 Conglomerate; cobbles as much as 1 ft in diam- eter of pegmatite, aplite, and granitic rocks in arkosic sandy matrix ____________________ 0—5 Total exposed thickness _______________ l, 463 Lower part of Tropico Group exposed in central part of Kramer Hills, east of U.S. Highway 395 (secs. 3 and 4, T. 9 N., R. 6W.) Thickness Member (feet) 5. Tufiaceous shale ___________________________ 5 Basalt. Includes a wedge as thick as 30 ft of tufiaceous shale lensing in from northwest; top about 65 ft below top of basalt _________ 360 Chert, thin-bedded _________________________ 10 Clay shale, gray to tan; contains 5 ft of dolomite near middle _____________________________ 190 Basalt (and shale?) _________________________ 13:1: 4. Dolomite; some lenses of black chert .......... 15 3. Clay shale and sandstone; some basalt near middle (member largely concealed) _________ 160:1: 2. Limestone; interbedded shale and chert _______ 58 1. Sandstone, tan, arkosic; contains scattered pebbles and cobbles of pre—Tertiary andesitic and granitic rocks ________________________ 260:1: Dacite vitrophyre, extrusive or intrusive(?) lens ____________________________________ 0—150 Sandstone, like that above. Conglomerated); no outcrops but loose pebbles and cobbles of pre-Tertiary quartzite, andesitic and granitic rocks. Tufl’ exposed in 80-ft shaft to south- east ____________________________________ 1005; Total exposed thickness, exclusive of dacite vitrophyre (estimated) ________________ 1, 321 72 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA R, 38 E? R. 39 E. ‘ - ' .15 - \ _, /\,\\ _ '\ “) ‘. ".\/\/ - \ (/\_\ l /\, \///\\7 I\/ I 21 \/\ <\, l I4 ’:/\\\\ “/ \ I // \\\/ -\\ SEA LEVEL SEA LEVEL A E _ a. /' _ \ / 3 \ I ’ B SEA LEVEL 9 2‘ / B E U c .2 n. 2000' E H SEA LEVEL 2000' - cl \ 2000' \ \ "\ / I \ \\ ”1/ \I‘ \\/\ \_\\/ q \ / ’ _ _ —\ / \ _ _// r -‘\;J\‘o Tropico Group 0 O 0 Oligocene (.9) and Miocene (-7) UNCONFORMITV E Pegmatite dikes in quartz monzonite J \/ \’/\ II Quartz monzonite PRE-TERTIARY o /, -\ WW :flnnra; -// ,\ All]? 2w ’— \x: W ' "L", \ 11 \ FIGURE 45,—Geolog'lc map and section of hills east of Castle Butte. l ,—\/\/\ T; \ ’1 > SEA LEVEL SEA LEVEL 239—655 0~67——6 74 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA ’"lV "FY/3(4) \/\/’~\’\/\/\/‘/ //\ (/7 /\/‘ /,\’ \/I/ \I,’ \ ’J 2 ~ ‘/\/.\’\“— \V—u ' r‘ ,L\//‘//\t, /\ \ ,\ /\\ l\l\l\—‘/\/ . 1 \ \/|\_,__ I‘- \/\/\, /\ \ x3. .;\>\’/\ % \(hi‘sa/xv‘: \ / _ \ — \\l \ / /\ \/ /\ \\ ,l, '/ \/ \l/ l 18 \/ ‘/ )1 _\ \ /l/\/\ E l \\ ‘il \ ‘/ — \ \U/ f / \/,\’r/ |\” /\/ s \— "CM/JAM» ‘~,I \ \ IH’ ,,//\\/\ ‘VU‘ ’\_/\/ ”’34 \ :3” ‘ \/ \ /\/ I79 '/\ /\ Rm Pleistocene Miocene Oligocene (.9) and Miocene (?) Tropico Group Ilzse 22 2 \.0 '\°.. 4" EXPLANATION 0 Alluvium Older alluvium Fanglomerate UNCONFORMITY o o a a o Granmc fan- 00000 ‘70 °o glomerate o ° - - (see sections) a u S h Sandstone 5 Clay shale (contains borates) Saddleback Basalt. 8 Clay shale and a cherty limestone h 6) B .3 Tuff UNCONFOPMI TV '56 ._Q\ . 5 a 270 " 0/ 2 -. \illflgnee 3E QUATERNARY (LS. HIGHWAY #66 Boron Quartz latibe dikes Pegmatite TERTIARY dikes Quartz mon zonite Porphyry //g/ Gneiss PRE > b 5 ‘ ‘0 ~ 3 “ c: < \ § : \ E a g a VP Wan/1,51 \ \l _\ ,\ \I/ /\ , \ m4 “31 a o v as N m‘ 05 ii I! H E ... 8 'g 0 E 0 ° 3 a: no .5 u 00 3 9° 0 n° 0 O 0 0 ' 0 . o +\ c 0 133 o “’0 I! 6 g .2: < E§ m $__ >- o 3'. N E i E .. II m ”II V L v . Eu)" -0” “to o ‘L D— n. < I III I: In x < 7—-.. L ' a: a L“, a 3'; 0 Sn 3% u 0 w 5:: 8-5 U 3 ° 0 2w 0 5: :2 5:: i< ”at, I: or: \ an: at: /\/_\/)\/ g8 /\A\/\//\:V /\/lC/\/\/ /\ /‘/ L/\/\ ‘1' 9Q! l I I I 8 8 b b C O 8 S m m N -4 SEA LEVEL SEA LEVEL VERTICAL AND HORIZONTAL EXAGGERATION X 2 Locations of sections are shown on figure 46. FIGURE 47.—Sections of Kramer borate district. 75 76 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Lower part of Tropico Group exposed in southeastern part of Kramer Hills east of U.S. Highway 395 (SE% sec. 11, N W% sec. 14,T. 9N., R. 6W.) Eastward along strike, member 5 becomes overlapped by Red Buttes Quartz Basalt; breccia of shattered quanz monzonite and diorite appears as lens as thick as 200 It at top of member 3; member 2 thickens southeastward to as much as 900 It (fig. 50); total exposed thickness about 1, 650 feet' in sec. 13 ’I‘ 9 N. R. 9 W. Thickness Member (feet) 5. Clay shale ___________________________________ 456 4. Dolomite, white; interbedded gray clay shale and thin layers of white magnetite ____________ 221 3b. Basalt; some clay shale in basal part ____________ 476 3a. Sandstone, light-gray ___________________________ 215 2. Limestone; minor interbedded shale and chert--- 43 l. Tulf _________________________________________ 160 Total exposed thickness ________________ 1, 571 Lower part of Tropico Group exposed in southwestern part of Kramer Hills just west of U.S. Highway 396 (sec. 16 and SEM sec. 17, T. 9 N., R. 6‘ W.) N orthwestward along strike, members 1 and 2 lap out against pre-Tertiary basement rocks (fig. 50) Thickness Member (feet) 5. Clay shale, gray to red ________________________ 115 4. Dolomite and interbedded shale ________________ 180 3. Sandstone, gray-white, arkosic; contains scattered grit and pebbles of granitic rocks and Tertiary rhyolitic rocks; some clay shale _______________ 45 Basalt, lens __________________________________ 0—45 Sandstone and clay shale (mostly concealed) _____ 80 2. Limestone and interbedded shale and chert _______ 18 1. Tuff _________________________________________ 15 Total thickness exposed (approximate)--- 498 Lower part of Tropico Group probably of early Miocene age or possibly of older Tertiary age, as indi- cated by position stratigraphically below upper part of Tropico Group that contains early middle Miocene fossils at Boron open pit mine. Pyroclastic lower unit of lower part of Tropico Group in Castle Butte and Kramer borate area and member 1 in Kramer Hills lithologically similar to and presumably correlative with Gem Hill Formation in Rosamond Hills. Sedi- mentary strata and basalt flows that constitute rest of lower part of Tropico Group presumably correlative with Bissell Formation of Bissell Hills. DAGITE At Desert Buttes, southwest of Castle Butte, dacite forms three isolated small volcanic plugs surrounded and partly covered by Quaternary alluvium, but pre- sumably intrusive through quartz monzonite exposed to south; rock light pink gray, felsitic; flow laminae and fracture parting are concentric around central core and dip vertically or steeply inward at each plug. At Haystack Butte, dacite forms single plug in quartz monzonite; rock massive, felsitic; contains small scattered phenocrysts of plagioclase (oligoclase) , quartz, biotite, hornblende, and potassic feldspar, in order of decreasing abundance. In Kramer Hills, dacite occurs as several masses in and near sec. 35, T. 10 N., R. 6 W., probably intrusive into lower part of Tropico Group along fault at north- ern margin of hills (fig. 50); rock generally similar to that of Haystack Butte, but pale pink gray and lacks hornblende. Dacite also present as lens of vitro- phyre in member 1 of lower part of Tropico Group in sec. 3, T. 9 N., R. 6 W. (fig. 50). Dacite presumably same age as lower part of Tropico Group, but possibly younger. SADDLEBACK_BASALT One or more flows of basalt that form middle part of Tropico Group in Kramer borate district; exposed discontinuously from Saddleback Mountain northwest- ward for 7 miles, and westward for 15 miles (pl. 1). Occurs under borate—bearing shale throughout Kramer borate mines except in extreme southern part; also struck in water wells below Quaternary gravel under alluviated valley within 5 miles north of Kramer borate mines. Named and described by Gale (1946, p. 346—350, pl. 52) and referred by him to Ricardo Formation (lower Pliocene) ; redefined as a formation and assigned to Pliocene( ?) (Dibblee, 1958c, p. 142). Type locality at Saddleback Mountain (in sec. 9, T. 11 N., R. 7 W.; see fig. 46). Northwestward from Saddleback Mountain, basalt about 200 feet thick, composed of several flows; rests unconformably( ?) on pyroclastic rocks of lower part of Tropico Group (figs. 45, 46). Art Stone House and Muroc Hills, Saddleback Basalt probably about 300 feet in maximum thickness and composed of several fine-grained flows. Overlies lower part of Tropico Group, probably unconformably (fig. 48). Under Kramer borate mines and westward, Saddle- back Basalt composed of several flows, in places sepa- rated by shale or sandstone (fig. 47) ; total thickness of basalt more than 400 feet, but not completely penetrated by any well. Basalt black, massive, aphanitic or very fine grained to ophitic (finely diabasic) ; aphanitic facies commonly weathers reddish brown. Rock composed essentially of plagioclase (calcic labradorite), augite, and olivine (largely altered to antigorite and limonitel), iron oxides, common scattered very small phenocrysts of labradorite; scattered amygdules of zeolites, calcite, or silica are other constituents. Saddleback Basalt now considered to 'be early Miocene in age, as suggested by probable conformable TERTIARY SEDIMENTARY AND VOLCANIC ROCKS R.9W. 117°45’ c)4 o5 16 0 13 14 0 o 5 19 20 O 3 0 U! A AI 1 — 3000' EXPLANATION /\ \ .-. — j — I /\ / — 2000’ r3/1K'39/Gc’3" - ~ W > _ /‘\_,,\\/\\\\/\\//\\ - —1000' § m /’\/\,\/\/_\\/ ,‘l, / _,,\\ \/\// (/ \_/ / n 4 ’,\/:~\,\ ‘\/\ \/‘ \\I/—’/\7\7|7\\:\/)/\q ‘/|/:/\' DE . 2 /\\/\/\/\/fl\/\/\/\// \ / \/,\\/\/\\//-\I_,‘/\//\/\/\/\/\‘/\’,\ SEALEVEL Alluvxum n: Lu § I- o < .§ 0 E Fanglomerabe 3000' - UNCONFORMITV ‘3‘; 2000' N: 1000' g a .3 ' a >- SEA LEVEL 3 Saddleback Basalt 2 01 a x o 5 ‘I “i ( “ = C“ — + + .§ E N § a a u D. §E E ° 0 9 ° w _ + + a E 3 0 g g Conglomerate Arkosic Tuffaceous Tuff F o sandstone shale ‘b 1 MILE L___—I—J UNCONFORMITV \ < Pegmatite dikes '11—: U] \(I j)! l"- '\\Q\m/\ [6:] D. Quartz monzonite FIGURE 48.—Geolog'ic map and sections of Muroc and Stone House Hills. 78 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 118°00’ ‘GC 00 c, 47,1») ‘ (VA/14: \/\’/ . 9.3/315/6’02» T- W n - ' 50 V N. . . . a : EXPLANATION >. E All ' E s uv1um Z ' DE r° y - ' E § Older alluvium < C). E 8 L ' ' :> 0 35'00’ UNCONFORMITV LEVEL and Miocene (?) i .s- B B Miocene (.9) Tropico Group Ah—ng a D = flu? n Fanglomerabe a a O D a KRAMER JUNCTION l_.___l___l E. >_ us Hwy (FOUR CORNERS) Ii Sandstone n: ‘65 F\ a. E E (’4\ D \ Clay _—... - “5 - . S \ shale I-Iul-l- Cherty limestone IL|_J Pegmatlte dikes E \ ‘9‘) E. m Approximate outline Fanglomerate . *— of concealed cole- I- , l g and sandstone n‘ \ /_\ 1| Quartz manzonltej E manite deposits 3 a. BI 25 26 28 29 36 394041 42 SEA LEVEL FIGURE 49.——-Geologic map and sections of Kramer Junction or east Kramer area. TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 79 relation to overlying beds that contain early middle Miocene vertebrate remains at Boron pit, or possibly older Tertiary. RED DUTIES QUARTZ BASALT One or more flows of quartz basalt form middle part of Tropico Group in Kramer Hills (pl. 1); also exposed at and near Red Buttes (the type locality, sec. 5, T. 8 N., R. 6 W.), for which it was named, and assigned to the Pliocene( Z) (Dibblee 1958c, p. 142— 143; 1960d, p. 101—102); described and mapped as quartz andesite by Bowen (1954, p. 78, 83—84, pl. 1). At Red Buttes, quartz basalt composed of several lava flows totaling about 300 feet in thickness rests directly on quartz monzonite; overlain unconformably by Quaternary fanglomerate. In Kramer Hills, quartz basalt forms one or several flows that total 360 feet in maximum thickness overlying lower part of Tropico Group with slight unconformity (figs. 49, 50). Basalt black on fresh surface, massive, hard, non- vesicular; in places somewhat brecciated; aphanintic to very fine grained; contains scattered small rounded phenocrysts 1 mm or less in diameter of quartz; smaller rectangular ones of plagioclase (labradorite) ; groundmm composed of labradorite, augite, diopside, glass, hypersthene, greenish-brown hornblende, and magnetite, in order of decreasing abundance (Bowen, 1954, p. 83—84). Quartz basalt now considered to be early Miocene age or older; probably correlative with Saddleback Basalt, as suggested by similar stratigraphic position and unconformable relationship to underlying lower part of Tropico Group. UNNAMED UPPER PART 01" T302100 GROUP A sequence composed mainly of clay shale, sand- stone, and conglomerate that conformably overlies lower or middle parts of Tropico Group in Kramer borate district, Kramer Junction area, and Kramer Hills. Not given formation status because of incom- plete and poor exposures and uncertainty of correlation from area to area. In Kramer borate mines north of Boron, sequence revealed by mine workings and exploratory test holes described in detail by Gale (1946, p. 335, 339—346, pls. 51, 52) and referred by him to Ricardo Formation (lower Pliocene) as used by Merriam (1914). Sequence conformably overlies Saddleback Basalt; about 800 feet in maximum thickness. Composed of three lithologic units as follows in ascending order: clay shale containing borate deposits, sandstone, and fanglomerate. Clay shale unit, described in detail as “Kramer Lake Beds” by Gale (1946, p. 335, 339—346, pls. 51, 52) ._ light dusty gray; in borate mines about 320 feet thick: contains all the borate deposits, mostly in middle part (as described on p. 126); overlies Saddleback Basalt throughout mine area except along southern margin where it overlies granitic-cobble conglomerate (fig. 59); grades upward through thin interbeds into over- lying sandstone unit, as seen in open pit of borate mines. Sandstone unit about 80 feet thick at Mudd borate (Western Borax) mine (Gale, 1946, fig. 4) ; about 150 feet thick at U.S. Borax Co. open pit; light grayish brown, friable, bedded, arkosic. Grades upward into overlying fanglomerate. Fanglomerate unit found only in drill holes in southern parts of mine area, penetrated to depth of 640 feet in shaft of Mudd borate (Western Borax) mine (Gale, 1946, p. 339, fig. 4) ; composed of unsorted granitic cobbles and pebbles in gray arkosic sand matrix; maximum thickness estimated about 500 feet. In foothills a few miles north of Kramer and Kramer Junction sedimentary sequence presumably of upper part of Tropico Group partly exposed, and penetrated in several test holes in adjacent alluviated valley (fig. 49) ; sequence similar «to that of Kramer borate district, but thicker, and rests directly on gran- itic bedrock. Most complete sequence exposed 5 miles northwest of Kramer Junction (fig. 49) as follows in descending order: Upper part of Tropico Group (8% sees. 14 and 15, T. 11 N., R. 7 W., 5 miles northwest of Kramer Junction) Older alluvium. Unconformity. Upper part of Tropico Group: Granitic fanglomerate; composed of unsorted sub- rounded cobbles and boulders of granitic rocks, 73:3" pegmatite, and aplite in gray arkosic matrix; occa- (fed) sional coarse gritty sandstone __________________ 350 Sandstone, light-gray, fine« to coarse-grained, mica- ceous, arkosic; upper 10 ft includes several layers as much as 9 in. thick containing pea-size pumice fragments; includes some interbedded micaceous shale in lower part ____________________________ 60 Clay shale, poorly exposed _______________________ 65 Limestone, gray, massive, sandy; includes some shale and chert; much brecciated ____________________ 15 Shale, clayey to tuflaceous; in places semisiliceous; thin-bedded, mostly gray, but locally white, yellow, orange, red, pink, purple; contains occasional thin platy beds of limestone ________________________ 180 Total exposed thickness ______________________ 670 Unconformity. Quartz monzonite. 80 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Recent < Pleistocene < Miocene < Oligocene (?) and Miocene (?) EXPLANATION FORMATION SYMBOLS Qa Alluvium Qf Fanglomerate 7 Upper part 6 Red Buttes Q Quartz Basalt § 5 U o 4 .2 n. 3 Lower part 5 2 1 O r Crystalline rocks ROCK SYMBOLS Sand and gravel Fanglomerate Conglomerate — ll Sandstone T. 10 Clay shale N. : / E Limestone _}\ _ l: (I \ //\ ‘1 / ‘u . |/_\7 .) ‘ Dolomlte W PRE-TERTIARY QUATER- NARY PRE- TERTIARY TERTIARY QUATERNARY TERTIARY TERTIARY SEA LEVEL SEA LEVEL SEDIMENTARY AND VOLCANIC ROCKS lg \/\/ \l l \/\ \_\l/ \\ \|\/ '/ SEA LEVEL \/\, /\/\\ SEA LEVEL SEA LEVEL SEA LEVEL |\I \/_\/\ / /f/ /‘> \ \ \/ _\/,, \7: \ , \\ \ //T/\ \I\/ /, _ \I\I\I \\/\l . _ , I I \f (N //~— \"\/1 /\ b ’ l\:‘/ \I)//\/ /'\ \L ”\l/ a) I\ /\ C \ \‘l E \/\I\/\/\7\/ , /\:/\\ \ ,I\l/_\ My \ o /\/\':I/|\l/ /\/\ 2000’ SEA LEVEL Locations of sections are shown on figure 50. FIGURE 51.—Sections of the Kramer Hills. 81 82 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA In test holes in sees. 22 and 30, T. 11 N., R. 7 W., shale unit at least 1,000 feet thick; contains thin layers as thick as 4 inches of colemanite near middle, but no limestone or chert; fanglomerate may be 1,500 feet thick in test hole in SW141 sec. 22, T. 11 N., R. 7 W. (fig. 49). In low knolls in sees. 21 and 22, T. 10 N., R. 6 W., uppermost basalt flow of lower part of Tropico Group overlain by shale and sandstone sequence presumably of upper part of Tropico Group (fig. 50) ; about 800 feet exposed just east of US. Highway 395. Sequence as follows in descending order: Upper part of Tropico Group (secs. 21 and 22, T. 10 N., R. 6' W., 5 miles southeast of Kramer Junction) Fanglomerate. Unconformity. “Mm” Upper part of Tropico Group: (fed) Sandstone, light-gray, arkosic ................... 150 Clay shale, gray, micaceous ..................... 100 Chert, opaline to chalcedonic, gray-white to translu- cent gray; commonly streaked with yellow, brown, red, black; contains silicified roots of reeds, palms(?) and other plants _____________________ 2—7 Clay shale, gray, micaceous ..................... 75 Granitic breccia (shattered quartz monzonite) _____ 50-107 Sandstone, light-gray, arkosic ___________________ 100 Total exposed thickness, upper part of Tropico Group ____________________________________ 530 Lower part of Tropico Group: Basalt ________________________________________ 350 Upper part of Tropico Group overlies Red Buttes Quartz Basalt; composed of micaceous gray clay shale, interbedded arkosic sandstone, and occasional thin flows of olivine basalt, unconformably overlain by Quaternary older alluvium (figs. 49, 50, 51). In southeastern part of Kramer Hills in W1/2 sec. 14, T. 9 N., R. 6 W., about 800 feet exposed (mapped as “upper lakebeds, Miocene” by Bowen, 1954, fig. 43, p. 78). Mammalian fossils found in upper part of Tropico Group from a horizon within 21-foot-thick sequence of tan sandstone and sil'tstone about 200 feet above top of borate ore body at Boron open pit mine by U 9. Borax and Chemical Co. This fauna, known as the Boron fauna, believed to be of early middle Miocene (early Hemingfordian) age; is older than the faunas from the Barstow Formation (Merriam, 1919), and close to the fauna from the Tick Canyon Formation of Jahns (1939; 1940) in Soledad basin (R. H. Tedford, University of California, Riverside, written commun. to S. J. Muessig, U.S. Borax and Chemical 00., April 28, 1964). This fauna indicates that upper part of Tropico Group is older than Pliocene age to which this unit was tentatively assigned (Gale, 1946, p. 335, 339—346, pls. 51, 52; Di'bblee, 1958a; 1958c, p. 138, 142). If so, it may be correlative with the unfossiliferous lower third of the middle and late Miocene Barstow Forma— tion of the Mud Hills of which the lacustrine facies is lithologically similar, or it may be older. LIMESTONE A low hill 2 miles west of Castle Butte is capped by about 50 feet of thick-bedded dark-gray limestone that rests on about 150 feet of tan-white tufi', presumably of lower part of Tropico Group (fig. 44). Limestone contains locally numerous concentric aggregates of calcareous algae( ?). Limestone formerly thought to be part of lower part of Tropico Group (Dibblee, 1958b), but it contains diatom remains that suggest Pliocene age, as reported by Kenneth E. Lohman (written commun., March 2, 1953). If this limestone is of Pliocene age, it is younger than the Tropico Group, and may be correla- tive with the Horned Toad Formation (Pliocene) of the Horned Toad Hills. ROCK UNITS OF EASTERN AREAS BARSTOW AREA UNNAMEDSEDIMENTARY ROCKS Unnamed sedimentary rocks of lacustrine and fluviatile origin exposed 5 miles south of Barstow; also as several isolated outcrops near Barstow and Len- wood; described by Bowen (1954, p. 79—80) and Dibblee (1960d). Sedimentary sequence exposed 2 miles west, 1 mile north, and 2 miles northwest of Barstow (fig. 5) con— sists of 5—20 feet of soft gray clay and pebbly sand- stone resting on weathered surface of gneiss and in turn overlain by 10—30 feet of unevenly bedded dark— greenish-gray to ocher-yellow ferruginous dolomite or limestone, in places cherty. According to Bowen (1954, p. 22, 104—105, pl. 1), limestone outcrop 2 miles northwest of Barstow yielded poorly preserved gastropod and echinoid debris of probable late Paleozoic (possibly Pennsylvanian) age; limestone asigned by him to Oro Grande F orma- tion, interpreted to have been thrust from northeast. However, fossils reported (specimens are lost, and repeated searches have been made for more but none ever found) either reworked or not certainly identified and therefore unreliable. Furthermore, limestone TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 83 R.ZW. SEA LEVEL SEA LEVEL 2000’ —- SEA LEVEL SEA LEVEL 9 2000' — SEA LEVEL SEA LEVEL EXPLANATION “ >- E { g a; Alluvium E g a o a T‘ I; § 0 ° 8 § Fanglomerate Marl and clay UNCONFORMITY [‘3‘ Rhyolice breccia i" : ...... Sandstone Clay shale Carbon- ate bed k—v—j TERTIARY FIGURE 52.—Geologic map and sections of Lenwood area. unmetamorphosed, totally devoid of any metamorphic crystalloblasts (T. H. McCulloh, University of Cali— fornia, Riverside, oral commun., 1963), lithologically similar to that of other outcrops of Tertiary age near Barstow and east of mapped area. Therefore outcrop now regarded as Tertiary in age, unconformable on Waterman Gneiss (fig. 5). Near Lenwood (fig. 52), at least 2,000 feet of sequence exposed; here mainly gray clay shale, some interbedded gray micaceous sandstone, and several beds as much as 5 feet thick of hard tan dolomite or limestone. In exposure 5 miles south of Barstow, unnamed fanglomerate (Rosamond of Gardner, 1940, p. 27 8— 281, pl. 2) on Daggett Ridge overlain unconformably by an unfossiliferous sequence 1,500 feet .thick. Extends eastward beyond border of mapped area and described by Gardner (1940, p. 289—290, pl. 2) as “Campbell’s Lake beds.” Basal 150 feet composed of gray-white tufi' of glass shards; remainder of green to red siltstone and sandstone. Separated from overly- ing Quaternary gravel by White marly limestone. DAOITE D-acite exposed as large mass 7 miles northwest of B'arstow, as several intrusive plugs at Barstow and in Waterman Hills (fig. 5), and as isolated outcrop 7 miles southwest of Barstow and also east of Barstow beyond east border of mapped area. Dacite of these areas pink to pinkish gray, por- phyritic, massive to flow laminated. Phenocrysts make up 20—30 percent of rock and are plagioclase (sodic andesine), quartz, and biotite; aphanitic groundmass is mainly plagioclase, sanidine, quartz, and scattered magnetite (Bowen, 1954, p. 87—88). Northwest of Barstow, dacite mass intrusive into pre—Tertiary rocks; in Waterman Hills, dacite intru- sive into pre-Terti'ary rocks and Pickhandle Forma- tion; rock massive in both areas. 84: AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA At Barstow, dacite plugs surrounded by Quaternary alluvial sediments; characterized by concentric flow laminae parallel to outer walls of each plug as indi- cated on figure 5. Beyond east border of mapped area, dacite intrusive into pyroclastic and sedimentary rocks similar to those of probable Oligocene or Miocene age. If so, dacite probably Pliocene( ?) but possibly Miocene in age. JACKHAMMER FORMATION A discontinuous thin basal sedimentary and volcanic formation exposed only in eastern Mud Hills; uncon- formably on quartz monzonite; overlain by Pick- handle Formation. Named and described by McCulloh (1952, p. 107—109) from exposures at type locality at J ackhammer Gap east of Mud Hills (Dibblee, 1967), and officially adopted for use in this report. About 150 feet in maximum thickness, best exposed in Owl Canyon (fig. 55) ; lower part 30—100 feet of red arkosic sandstone "and siltstone; in places sandstone contains smoothly rounded cobbles of quartzite and granitic rocks; upper part 5—20 feet of bedded white tufl’, overlain by 5—30 feet of vesicular basalt. Half a mile east of Owl Canyon, formation composed of lens as thick as 50 feet of gray limestone; farther east composed of granitic-boulder conglomerate. Formation unfossiliferous; older than Pickhandle Formation; presumably Oligocene or early Miocene in a e. g PICKHANDLE FORMATION A sequence of mostly pyroclastic rocks exposed in Waterman Hills 4 miles north of Barstow, in Mud Hills, Opal Mountain-Upper Black Canyon area, and Gravel Hills (pl. 1) ; rests on eroded, weathered surface of pre-Tertiary crystalline rocks, except in eastern Mud Hills where it conformably overlies J ackhammer Formation; formation first recognized in Calico Moun- tains, where mapped and named by McCulloh (1952, p. 114—125) after Pickhandle Pass, the type locality, in Calico Mountains (Dibblee, 1967). Oflicially adopted for use in this report. In Waterman Hills (fig. 5), formation is about 3,700 feet thick; composed of about 800 feet of tufl' breccia at base; overlain by about 400 feet of dark- red-brown flow breccia of rhyolite or dacitic felsite that extends from larger volcanic mass to southeast; in turn overlain by about 2,300 feet of tan tufi' breccia containing felsitic fragments; at top about 200 feet of gray conglomerate of granitic and dacitic cobbles. In Mud Hills (figs. 54, 55) on north flank of Bar- stow syncline, formation about 2,800 feet thick; com- posed of conglomerate, tuff breccia, granitic and rhyo- litic breccia, sandstone, and andesite, in somewhat variable stratigraphic order as shown, and as described below. Conglomerate as thick as 600 feet forms lower part of formation; gray, poorly bedded, composed of boulders and cobbles of quartz monzonite in friable matrix of arkosic grit or sandy tuff breccia. Includes some thin lenses of gray to red arkosic sandstone. Tufl' breccia forms middle part of formation, as much as 1,150 feet thick; also present in upper part; white, greenish white to buff white, thick bedded, fine to medium grained; contains angular fragments of brown porphyritic andesite and lapilli of soft devitrified pumice. Granitic breccia and rhyolitic breccia (fig. 55) together form as much as 1,100 feet of upper part of formation. Granitic breccia composed of shattered quartz monzonite; forms thick massive resistant light— gray to reddish-gray lenses, some as thick as 500 feet. Rhyolitic breccia composed of shattered massive white rhyolitic felsi-te; forms local thinner white lenticular intercalations within granitic breccia. Andesite forms lenticular flow at top of formation near Barstow-Goldstone road and on south flank of Barstow syncline 2 miles west of that road; massive, brown, porphyritic; contains phenocrysts of plagio— clase and basaltic hornblende in aphanitic groundmass. Rhyolitic breccia (fig. 54) in northwestern part of Mud Hills about 500 feet thick, rests on quartz mon— zonite; indistinctly bedded, yellowish brown; com- posed of angular fragments of tan rhyolitic felsite. In vicinity of Williams pumicite quarry 6 miles east of Opal Mountain, formation about 250 feet thick; composed of bedded white to orange—buff pumiceous tufl' ; pumice fragments as large as 3 inches in tufface- ous matrix. Overlain by rhyolitic flow breccia of Opal Mountain Volcanic Formation. In Opal Mountain—Black Canyon area (fig. 53), Pickhandle Formation about 2,800 feet thick; com- posed mostly of white bedded tufi‘ ; lower part associ- ated with rhyolitic intrusions and flow breccias of Opal Mountain Volcanic Formation; contains two basalt flows, one as much as 250 feet thick, and con- glomerate lenses, as much as 50 feet thick, of either volcanic or granitic detritus, and a 10—foot lens of chert and limestone. Tufi' medium to fine grained; contains grains of quartz, feldspar, flakes of biotite, lapilli of devitrified pumice, and fragments of rhyo- litic felsite. Grades upward through thin intercala- tions into shale of overlying Barstow Formation in Black Canyon. Recent F—H Oligocene (.9) to Miocene Pleistocene rh/L_—\ A Miocene Ba Pickhandle Opal Mountain EXPLANATION D . Alluvium U Older alluvium Black Mountain Basalt UNCONFORMITY TERTIARY SEDIMENTARY AND VOLCANIC ROCKS \ ‘1: R445 R.45E QUATERNARY : .2 h . . ,4 g Shale Sandstone Fanglomerate n UNCONFORMITY ‘3 + + + >- n + + + a: E + < L2 Tuff Chen Conglomerate Basalt l- >. UNCONFORMITY n: n: 5 E \ / I < '5 ”mum ; E _ l \ tr 3 Rhyolitic Rhyolmc felsite Perlite Quartz monzonite E 0 1 MlLE 5‘ breccia plug (lines indicate “'1 E trend of fracture a: 3 cleavage) “- "0' AI > 4000' 4000' Black Canyon )( 2000, 2000' Perlite digging 0 SEA LEVEL SEA LEVEL Agate digging / 4000, 4000' 2000' 2000' SEA LEVEL SEA LEVEL FIGURE 53.—Geologic map and sections of upper Black Canyon and Opal Mountain area. 85 86 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA In Gravel Hills (fig. 56), formation composed essen- tially of white tufl' associated with rhyolitic flow brec- cia and intrusions of Opal Mountain Volcanic Forma— tion as in Opal Mountain-Black Canyon area; total thickness of wit about 700 feet; includes several lenses as much as 200 feet thick of conglomerate of granitic cobbles and boulders; basal part includes some conglomerate of perlite detritus. Southwest from Black Mountain and Gravel Hills, Pickhandle Formation presumably thins out beneath Harper Valley as indicated by its total absence above pro-Tertiary crystalline rocks in several test holes on and near Harper (Dry) Lake (table 3), and in hills southwest of Harper Valley. Formation unfossiliferous, but older than uncon— formably overlying Barstow Formation of middle and late Miocene age; similar lithologically and in strati- graphic position to, and therefore presumably correla- tive with, Kinnick Formation of middle and possibly early Miocene age of Monolith and Cache Peak area. and to Gem Hill Formation of Oligocene( ?) to middle Miocene( ?) age; Pickhandle Formation «therefore most likely of Oligocene( ‘9) to early or middle Miocene age. OPAL MOUNTAIN VOLCANIC FORMATION Volcanic rocks of rhyolite and quartz latite compo— sition occurring as intrusive plugs and extrusive flow breccias in pyroclastic rocks of Pickhandle Formation in area of Opal Mountain and upper Black Canyon and in Gravel Hills (pl. 1); mapped and described separately as Opal Mountain Volcanic Formation; named for Opal Mountain; type locality in vicinity of Opal Mountain and forks of Black Canyon to north- west (Dibblee, 1967; fig. 53, pl. 1). Officially adopted for use in this report. Formation composed of following three facios: rhyolitic felsite, rhyolitic breccia, and perlite (figs. 53, 56, 57). Rhyolitic felsite pink to tan, massive to flow lami— nated, aphanitic to slightly porphyritic; contains scat— tered small phenocrysts of plagioclase (oligoclase- andesine) in microcrystalline groundmass of ortho- clase, quartz, and plagioclase in order of decreasing abundance; forms intrusive plugs or necks commonly with concentric flow laminae and fracture parting parallel to outer walls of each plug. In Black Can- yon, several very small plugs composed of bufi' pumiceous felsite. Rhyolitic breccia mostly dark-brownish red, locally brown to greenish brown; composed of angular frag- ments of massive to flow-laminated rhyolitic felsite embedded in felsite matrix; occurs as outer zones at margins of some intrusive plugs of rhyolitic felsite, but mostly as large volcanic piles and flow breccias wedging out into tufl'. Perlite, steel gray, glassy, massive, with numerous curved fractures; forms chilled zones as thick as 30 feet around margins of some plugs of rhyolitic felsite and at base of some rhyolitic flow breccias; perlite commonly grades into both these facios through tran- sitional zones of dark-reddish-brown subvitreous fel- site containing spherulites and nodules filled with silica (chalcedony and opal). Perlite most prevalent in Opal Mountain-Black Canyon area (fig. 53). Volcanic rocks emplaced during time of deposition of Pickhandle Formation and therefore of same age. BARSTOW FORMATION A terrestrial sedimentary sequence of Miocene age; exposed in Mud Hills and Gravel Hills. Exposures in Mud Hills named Barstow Formation by Merriam (1915, p. 252—254; 1919, p. 441—448); mapped and described in detail by writer (Dibblee, 1967). Type section designated as south-dipping sequence in eastern Mud Hills just west of Solomon Canyon, in sec. 20 and N% sec. 29, T. 11 N., R. 1 W. (approximately along section line B—B', fig. 55) measured and described in detail by Durrell (1953, section A—A’, pl. 4, fig. 12). In Mud Hills (figs. 54 and 55), formation ranges from 2,000 to 3,000 feet thick; folded into major syn— cline generally known as Barstow syncline; uncon- formably overlies Pickhandle Formation in places with angular discordance as much as 25°; eroded top unconformably overlain by generally flat—lying locally granitic older Quaternary alluvium. Basal part of formation is conglomerate on north flank of Barstow syncline, conglomerate as thick as 250 feet, overlain by algal limestone; on south flank conglomerate greenish gray to red; as thick as 900 feet, base unexposed; includes some interbedded sandstone and shale. Basal conglomerate overlain by about 1,700 feet of interbedded clay shale and sandstone. Sequence includes occasional beds few inches or few feet thick of hard cream-white impure limestone or dolomite and white fine- to medium-grained rhyolitic tufl ; one bed at top of sequence as thick as 5 feet and forms prominent white marker. Sequence changes markedly along strike; on south flank of syncline entire sequence grades laterally westward into poorly TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 87 bedded brownish-gray conglomerate and some fanglomerate in southwestern Mud Hills. Sequence west of Solomon Canyon (type section) generalized as follows in descending order: Type section of Barstow Formation, west of Solomon Canyon (sec. 20, N}’2 sec. 29, T. 11 N., R. 1 W., fig. 55) Older alluvium of Quaternary age. Unconformity. Barstow Formation: Conglomerate and sandstone, light-gray—brown, con- tains cobbles and pebbles mostly of granitic rocks, 7113' some of quartzite, hornfels, and andesite; lower (fed) part mostly sandstone _________________________ 448 Limestone, gray, locally cherty ___________________ 28 Sandstone, light-gray, bedded ____________________ 50 Tufl, white _____________________________________ 4 Clay shale and sandstone, interbedded, yellowish— to light-greenish-gray; clay shale predominating; includes occasional thin strata of hard nodular impure limestone and soft brown bentonite_-___ _ _ 1, 314 Tufl", white _____________________________________ 0-4 Sandstone, light-gray, contains scattered lapilli of pumice_ _____________________________________ 140 Algal limestone, dark-gray, irregularly bedded; com- posed mainly of calcareous algae or tufa? ________ 30 Conglomerate, greenish-gray; clasts mostly of gra- nitic rocks, few of pegmatite, aplite, and andesite- 137 Total exposed thickness, Barstow Formation- __ 2, 155 Unconformity. Pickhandle Formation. In Gravel Hills (figs. 53, 56, 57, and pl. 1), Barstow Formation overlies Pickh-andle Formation conform— ably in lower Black Canyon, unconformably elsewhere; to north it laps onto pre-Tertiary plutonic rocks. For— mation as thick as 4,500 feet in southwestern Gravel Hills adjacent to Harper Valley, but thins rapidly northward. In lower Black Canyon 3 miles above mouth and in core of anticline to west, lowest 500 feet of Barstow Formation composed of thin-bedded light-gray shale that grades upward through bufi' sandstone into coarse fanglomerate that makes up bulk of Barstow Formation of Gravel Hills. Fanglomerate composed of two distinct facies: one of granitic detritus, the other of volcanic detritus. In southeastern part of area, granitic fanglomerate inter- tongues northeastward into volcanic fanglomerate (fig. 57) ; in northwestern part, volcanic fanglomerate occurs as lenticular mass within granitic fanglomerate (fig. 56). Both facies composed of unsorted sub- rounded to angular fragments as much as 8 feet across in weakly consolidated light—gray coarse sandy matrix. Fanglomerate of granitic detritus light gray; most fragments of granitic rocks presumably quartz mon- zonite; other fragments of aplite, pegmatite, quartz diorite, hornblende diorite, and gray to tan porphyritic and felsitic igneous rocks of pre-Tertiary age. Fan- glomerate of volcanic detritus light-pinkish gray; most fragments of reddish to pinkish brown massive to laminated rhyolitic and felsitic volcanic rocks of Ter— tiary age; other fragments of Tertiary brown andesite porphyry, basalt, volcanic chert, jasper, and opal, rarely of pre-Tertiary granitic rocks. In Mud Hills, uppermost part of Barstow Forma- tion (part above marker tufl' bed) yielded one of largest vertebrate faunas in North America. Fauna first studied and described as Barstow fauna by Mer- riam (1919, p. 441—448) who determined it to be late Miocene in age, definitely older than Ricardo (Claren— donian) fauna. Strata containing Barstow fauna regarded as type for Barstovian Stage, upper Miocene (Wood and others, 1941, p. 12; Savage and others, 1954, p. 48—49). Fossil material collected by members of US. Geo— logical Survey from 11 localities in Barstow Forma— tion of western Mud Hills (fig. 54) under study. Nine localities from upper part; two from middle part; lower part unfossiliferous. Preliminary studies indi- cate upper part late Miocene (Barstovian); middle part middle Miocene (Hemingfordian) in age (Lewis, 1964). In eastern Gravel Hills just northwest of lower Black Canyon, four localities (two shown in fig. 57) yielded remains of several mammalian species of late Miocene (Barstovian) age. Sakel palm, similar to existing palms in warm parts of northern Mexico (Savage and others, 1954, p. 48) only kind of plant remains found in Barstow Formation. Fresh-water diatom remains found by K. E. Lohman in lacustrine clay shale within 1,700-foot interval between basal conglomerate and marker tufl' bed on south flank of Barstow syncline in south central Mud Hills, and in clay of 100-foot interval starting at 20 feet stratigraphically above tufl' bed northwest of lower Black Canyon near vertebrate fossil locality shown on figure 57. Preliminary study indicates assemblage from Black Canyon locality to be composed of 35 species and similar to assemblage from Virgin Valley Beds of Merriam (1907), Barstovian age, of Humboldt County, Nevada (K. E. Lohman, written commun., 1955). AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA 88 EXPLANATION f \ [J Basalt Black Mountain Alluvxum Older alluvium Wig >Km<_._.w_m._. Tuff bed °o a Sandstone Conglom— Limestone erate bed Shale j|\ :oEaEuch 33m~am < >Lqm.m M hvhc a 7 0c M m<_._.mm.r .mmn. x} / Granitic rocks 8 EA LEV E L 4000’ 2000' SEA LEVEL .—Geologic map and sections of western Mud Hills. FIGURE 54 89 TERTIARY SEDIMENTARY AND VOLCANIC ROCKS /\\ TRONTIA NI‘TE _ FROSPEC‘I.’ 117' \ RV1 w.V§ ’- >7‘\//I/\‘ 2W —(\‘4'/;\/I;/ . ~ . o. a. m I . v‘ ., m3 o... I 0 ob \ \ >Km<_._.mm_._v + . m m .m _ m + :1 lo. w a M by m An. ¢ T R b A w m m + + + a A D m m m m i f 1 e m S S .d f C v . m V 3 d e .m + + + u u v o e n m + + T r 4 1 IL m . a .1 ++ b v A n l S L 0 L m w c , m I f . o a m M c a m .m m b e a o . e R m .m .w t .m a a cu m 0 n c 3 any n h o F e d l S noun m. w mm n a u a a C a .d S aw W B n :ofiuEho’m aim—“Buck 5:33.87..— Boumunm \ 295‘:qu hwfifiasxodh. 2393: Q8383 3 a.» ufiwgoufic SEA LEVEL >m<_._.mm._. ——Geologic map and sections of eastern Mud Hills. 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I d>m._ «um fl«PM«GED,vxin.VIQNwa/OCumx‘vwh/IAVXx, an: I . . . . .\.\| Il|lll I «K I «1:111 LG \IJ/ozflalluncn I_:v_»1_\_vr7.v_»rx/, I . .2\\\ ... . . . . . ..... / U: _\./\ //\/I\/\_\ SS \ e + + ++ + + IIV.) >9 \ I 77¢? /.\//\. /_\‘ 09$:\.u.I/.\I\7:I\\.I\..I H +++ + + + + + + 4 C27 GIG/.Iv/vVHTTTDF I\\:.\, ‘1] II//\ I\ LI\ .. \I .\/\,\.\\ \QVLl . .v/FIHQVU I: 7Cfiv7 ooov \ \/l\ _ .83 77.\ G9 608 .88 RN m $5.. «mm .65: (mm \ < I - \I/PP/rfi. .oOON .oooq . ,JQKI/IIXJIQ/I . . .n.\;;. I l lllll l .88 +++++<+<+ P+++<++++++++ .+........... +++++++++++.... boov boom EXPLANATION A ' 4000' is 1:] u , -— II k~ 32 § Alluvmm \‘ \\\\ \\ \/ // ’ ll_\:l‘/—\I < uNcoNFORMITV = \\ ’/ 9 § 4 ” \, #9330396, 2000' 2 II ¢\\/ \\ // ”a“ Kl a,\/\—, m =\\\\ l 4\ ‘\\-\ “/x‘AZJ -\ m< § \ § \ \ v A ‘//\l/—‘ \/| / '— u \/§ ,, 4 x \\ \\ \\ \_. r~ 7) 4 _’ “El/\T;J7$€;/\§L ,, 5 § Landslide rubble ’ \ ’ L " ' SEA LEVEL 0 § °. 0 , Older alluvium 4000, E Afifiwfi W—A‘fi A Intrusive Extrusive andeslte andesite Intrusive. Intrusive E rhyolitic felsne basalt E ,§ (plugs and dikes) (dikes) g E p— ' filll m I “J . . . . E: g l‘ Granltlc breccm Basaltxc :75 and conglomerate azglomerate .% g .5 *6 K + " :4 Ln 9.. ‘— Tuff breccia Extrusive basalt g = “g \\ / x a . .' \ l |\\ \ E :3 E 9;: E,“ JA ’ +1 * N1: 5' 5‘ G .. 1 ug //==\\: V’) l/, m 30‘ ‘ *+*‘- 1‘ ranmc cong omerate g _ II §§ 4‘ ° 30 \ . +\\‘: k § and sandstone g \= ,/ o‘ ’\ / I _\/\ “10‘ = '15::va- 5 UNCONFORMITV \‘L‘ . \\ V) ‘\ 1" l—\\/\\_\ m \ \ ’— // — ' l ’ \, _’ >- [\J‘ \\ , § ’ —‘ ‘ - \, \ E — ‘V‘ II” \\‘=’=“~=/'I\ ‘V/‘fi/V‘ ‘1x/ 00 L ; I: Quartz monzonite Crushed grano— Granite Granite = 4“: {2'1"} \ (x \ \; _\’ ’ 0 \l _ 2’ + ’(‘1 m and granodiorite diorite aplite 4 ’/ ’l ' 7" / \ \ I, a a ‘—_ ’: ”JV/L w " ‘ -/"'\ 0' ° 1&0 a’z‘T/ 5 ° \ . s‘ m’ ":2 . E Quartz diorite and Homblende e 0 / ° .l",////g :2 ’2“ v migmatic gneiss diorite §5 u \\ ‘0 0 Y‘ ‘1 / \Ill [$1.5 E:— V \\II ==§ fi§§=\\ §'=\ll/,\’/ “'33“ 6’ /°. ‘_'_+ i:: *1:: ~ — ' ‘\ . _::: + ¢ \ ;n\ ”1 I" u ’ 24:: 93: 0 ‘15 IMILE T\=': \\‘//§I:‘;¢ ./ IA:+:_‘E.—:-_:+: \ l—_.L_.___ .._J §\\‘ = // =:II¢’=\\ ' a ‘32 ::EE V< \ ‘b' 4 - '1' : ’z A + __ = :5 \l A 32:62 E + :: —‘ E A : :‘z 5.3% + E t. =. D 1 ’ E ' + 1721': + + a- ’ / 1‘3 Z 35 13 I, — 1 _ Q I, A __ \ \ / -_ 1 7391/ :IL'ILV ,|>I\/\ \ ’L’. <| ‘ c ‘x- goo-fin, 1‘” -~ \ 55/? ‘ '47' av mph/TI/(CZD I V 7“” .|\ \I\ (A ”I UNCONFORMITV TERTIARY SEDIMENTARY AND VOLCANIC ROCKS \/\/\ , ’l‘~/| \ a ,_ 1 Chuckwalla ) sMountaln ) a ,_ \_ /\ \ l’\/ /\/ ’l. J 37 T I5 7\ [\L 1 <\ , / ,_ — \1 / x, ‘ I I‘ (x \ \/ I z - _\ :\ _ _, —’\'/ I‘ \l ‘03” V ,‘L\’_\’l:i/\I\/ "U’ --—" l‘ 7\/\ ’.‘/\‘ \.’\/\‘ — c" \\/\.,-17‘ \l\/ 7\\/‘\/— ‘ \/\’ _ ‘ |’\‘,’ $ , / /, I, ‘ a . \— ., \ | ’1\\/ I‘A.‘|/\/ \/ NV, \1'f\ /\ I_ / /::\-;‘_\‘;{//\’/_\\,/‘1,\ "mil: _ \ ’ \,,’ \\"\l‘:“/ z,\ \ — , \/ /~_ \ \ /\ |/.|‘ ,\ /‘\ ,\/,_,-__ / f‘l /\. \/,\1, a \, \ IL‘\J’_\’:/~\xj \/\‘/l’\\,-\l:' \~ q/ /_/’;:\\ 7\\::\ Chi’v R 35 E. R 36 E FIGURE 61.—Geologic map and sections of Jawbone Canyon area, southern Sierra Nevada. 98 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA hills northwest of Mojave; named after Horned Toad Hills southwest of Warren railway camp (Dibblee, 1958c, p. 143, 1959b), Type section in Horned Toad Hills, from base of formation about 7,000 feet S. 700 W. of Warren railway camp south-southeast 1 mile to top of formation (fig. 62). Formation about 1,050 feet in average exposed thick— ness and composed of three parts or members (fig. 62) ; sequence and lithology of members shown below; thickness given are at type section, but along strike maximum thickness of upper member 90 feet, of middle member 130 feet, and of lower member 800 feet. Horned Toad Formation, Horned Toad Hills (fig. 62) Sand and silt of older alluvium, Pleistocene. Unconformity. Thickness Horned Toad Formation: (feet) Upper member: greenish-gray argillaceous gypsifer— ous clay _____________________________________ 80 Middle member: limestone, shale, and sandstone, interbedded. Limestone white, soft, marly; forms strata as thick as 2 ft. Shale greenish-gray, soft, sandy; forms strata as thick as 5 ft. Sandstone green, massive to bedded; composed of ill-sorted fine to coarse grains of quartz and feldspar in clayey matrix; forms strata as thick as 5 ft; in places contains thin layers of gray volcanic ash _________ 75 Lower member: mostly buff friable fine- to medium- grained arkosic sandstone. Includes interbedded light-reddish gray sandy clay and siltstone in upper and middle parts; pebbly sandstone and conglom— erate in lower part contain pebbles and cobbles of granitic rocks and few of bleached platy felsite; locally at base contains lens as thick as 70 ft of con- glomerate of granitic cobbles and boulders _______ Unconformity. Quartz monzonite intruded by rhyolitic to andesitic felsite. 900 Vertebrate fossils (Warren fauna) collected by pale— ontologists from University of California, Berkeley. from two localities within 2 miles southwest of Warren railway station, presumably from middle member of Horned Toad Formation, most closely allied ‘to Cali- fornia faunas of middle Pliocene (late Hemphillian) age (R. H. Tedford, D. E. Savage, University of Cali- fornia, Berkeley, written commun. Nov. 23, 1960). EL PASO MOUN'IJAINS AREA GOLER FORMATION A fluviatile clastic sedimentary formation of early Tertiary age unconformable on pre—Tertiary plutonic and metamorphic rocks and unconformably overlain by Ricardo Formation in El Paso Mountains (pl. 1, figs. 64—66); mapped, described, and named after Goler Gulch (Dibblee, 1952, p. 19, 22—25, pl. 1); referred to Rosamond Series (of former usage) by Hulin (1925, p. 42, pl. 1). Goler Formation ofiicially adopted for use in this report. Type section from base of formation in Goler Gulch in NE1/1, sec. 34, T. 28 S., R. 39 E., or 2 miles sou-th- southeast of Holland Camp, north up Goler Gulch, over low pass, and down canyon draining due north nearly to gravel quarries in sec. 32, T. 27 S., R. 39 E. (fig. 65). Goler Formation as much as 6,500 feet thick; thins northeastward. Basal conglomerate as much as 500 feet thick between Goler Gulch and Iron Canyon; com- posed of smoothly rounded cobbles of quartzite, chert, hornfels, porphyries, and granitic rocks in sandy matrix; remainder of formation composed of bufl' to locally red arkosic sandstone and some interbedded green to red siltstone; grades laterally eastward into cobble conglomerate similar to basal conglomerate. Plant remains reported from Goler Formation con— sidered to be Eocene in age (Dibblee, 1952, p. 25). Primitive vertebrate fossils (Laudate fauna), reported from two localities near top of Goler Formation north of Goler Gulch, considered to be of Paleocene age by McKenna (1960). Goler Formation therefore now considered to be Paleocene and Eocene in age. mom: Dacite present as small exposure south of mouth of Jawbone Canyon and just east of Sierra Nevada fault (fig. 63). Occurs as flow breccia and some irregular lenses of white tuif breccia; at least one plug with flow laminae concentric around its central core. Rock of plug pale pink gray, flow laminated, felsitic; con- tains scattered small phenocrysts of plagioclase, quartz. and biotite; breccia similar but darker, massive. Dacite overlain unconformably by coarse conglom- erate of Ricardo Formation, therefore older; either correlative with tufi' (member 2) of Ricardo Forma— tion in Last Chance Canyon, or possibly with Kinnick Formation to west in Jawbone Canyon. RICARDO FORMATION A sequence of terrestrial sedimentary and volcanic rocks unconformable on Goler Formation and pre- Tert-iary rocks, and overlain by Black Mountain Basalt (Pleistocene?) in El Paso Mountains (pl. 1) : named by Merriam (1914, p. 276, 278; 1917, p. 430—443; 1919, p. 447—448); described and mapped by writer (Dibblee, 1952, p. 25—30, pl. 1); type section between Redrock and Last Chance Canyons. Formation composed essentially of detrital sedimen— tary rocks ranging from coarse fanglomerate to fine clay and chemically deposited siliceous and calcareous sediments; includes tufi'aceous rocks and flows of basalt and andesite. Basalt similar to that of Kinnick TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 99 R 34 E. R. 35 E. >. Terrace gravels E Z E Older alluvium E '2 § < D g o 4000' “‘ Gravel 2000' WWW Sand and silt , Horned Toad Formation SEA LEVEL B! 4000' g .§< E Limestone, clay, E 2000, and sandstone MS— L: Lu ,_ ' SEA LEVEL Sandstone, siltstone, and basal conglomerate a? r" \. I] § 0“ § 3 av“ : ' 40W g Rh Lil't' f 1 ‘te V't h ‘ yonc e91 ’ lropyre E and porphyry 2 _ , ' \ O 2000 I\ \I/ / \ , N ‘ O _ U) Quartz monzomte Lu SEA LEVEL 2 FIGURE 62.-—Geologic map and sections of Horned Toad Hills area. 100 and Bopesta Formations. Andesite red brown, hard, massive, locally brecciated, aphanitic to porphyritic, phenocrysts mainly of plagioclase (andesine), few of hornblende (largely altered to chlorite and limonite) ; groundmass microcrystalline to glassy. Westward from Last Chance Canyon, formation about 5,700 feet thick; thins northeastward to about 400 feet on east side of Black Mountain; farther east only few tens of feet thick, and in places absent. Divisible into eight lithologic members with distribu- tion and variations in thicknesses and lithology as shown.(figs.63,64,and.66y Stratigraphic sequence of Ricardo Formation in descending order as follows, starting from type section between Redrock and Last Chance Canyons: Sequence of Ricardo Formation between Redrock and Last Chance Canyons (figs. 6'3, 64) [Two figures in parentheses indicate thickness range, single figure indicates thickness at type section] Quaternary alluvial sediments. Unconformity. Ricardo Formation: Member 8. Gravel and sand, gray- white, weakly consoli- dated; of granitic detritus; contains andesitic cob- bles in basal part east of US. Highway 6; onlaps westward onto granitic basement of Sierra Nevada ________________ 7. Sandstone (in Redrock Canyon), lightrgray; of granitic detritus; contains interbedded greenish micaceous clay; grades northeastward into light- gray nodular clay con- taining frequent interbeds of gray—white lacustrine carbonate rocks and opaline chert; southwest- ward in Jawbone Canyon area grades through bed- ded conglomerate into coarse fanglomerate of granitic and some vol- canic detritus derived apparently from Sierra Nevada uplift to west____ 6. Conglomerate and sand- stone, interbedded, gray to pink; composed chiefly of volcanic and minor granitic detritus; north- eastward from Ricardo becomes pink volcanic conglomerate and thins out ______________________ Thickness (feet) (1, 000—2, 000) 1,000 (2, 000-2, 500) 2. 000 (0—600) 400 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Sequence of Ricardo Formation between Redrock and Last Member 5 . 1 2.2 Chance Canyons (figs. 63, 64)—Continued Basalt, amygdaloidal ______ Sandstone and clay, light- to greenish-gray ; hard beds of gray-white opaline chert and limestone near base ___________________ Basalt, amygdaloidal ______ Sandstone, prominently stratified, light-gray; some beds brick red; includes some interbed— ded green clays; few of gray-white impure lime- stone; in Last Chance Canyon, six beds of white volcanic ash 1—9 ft thick- Tufi' breccia, pinkish—white, thick-bedded; composed of pumice lapilli and andesite fragments in matrix of fine-grained tuff ____________________ Conglomerate, pink-gray; of vol- canic detritus; well stratified; con- tains much interbedded light-gray to red sandstone, especially in upper part; contains lens 0—20 ft thick of basalt and lens 0—30 ft thick of white tufi in lower part between Redrock and Last Chance Canyon _______________________ (0~800) Basalt; occurs as several discontin- uous lenses at top _______________ (0—30) Tufi breccia, white to pink, thick- bedded to massive; composed of fragments of pumice and andesite in matrix of massive fine-grained tuff; includes one to several len- ticular flows and flow breccias as thick as 100 ft of dark reddish- brown andesite _________________ (0-700) Tufl‘, white, well-bedded, medium- to fine-grained; locally altered to bentonite ______________________ (0—50) Conglomerate, greenish-gray to locally reddish-buff; composed of granitic detritus, some metamor- phic detritus, and reworked clasts from conglomerates of Goler For- mation; includes some interbedded sandstone; buttresses out south- westward _____________________ (0—400) Total thickness of Ricardo For- mation at type section _______ Angular unconformity. Goler Formation and pro-Tertiary rocks. I Thins northeastward. 1 Onlaps and pinches out southwestward. (0-100) (0-130) (0-100) (0—600) (0-150) Thickness (fat) 30 100 600 600 10 700 40 200 5, 710 TERTIARY SEDIMENTARY AND VOLCANIC ROCKS EXPLANATION I _._ _...\ AHVNHELVHO f—Ab_\ .-\ a a??? . " ’r 0“ n - v. 0 M4,, « an. ’3)" ‘ ~ ’/ \” Illn‘r‘q ‘ \IIIIII H- 3 ~ "*s*“1§“‘"* |=o.\\_u‘“§u,,‘ _ ‘ § ‘ '\ |'\ fill? /.. .\' AHVILHEL (SONS/7035‘ OIHdVdS/JVHJS V LON! s N E I E a -A U 8 0 I: u: “-4 8 "E E :3 '0 E "‘ 3:: g >. 'u .5 a ABVILHEL‘EHd E w E g B .51: E E ‘3 g .2 2 a): 3 3 g a: Q 3 8 'H 3:: 'E ‘E 3 E: 5%“E%.§“'g sa§g=§2§ 3; awfia3$§e waggwés §2>§§§§figafigaaEv3E§§a : g V7‘, 75 w 'H a J! a. Q "= '“ :3} G o o no 3 a o o 2'; I] : ++: 00 "o \ ++. 0° :2 H 1 1* (“011.0154 Maqwaw (nus Menus-1mm) uouuuuod opmom WWMJ AHVNHELVHO “’ka : a 3 w m " E ,n .— n E 5 E '5 g E 8 3 ° .2 E i E > L. x E s. :3 t E < p—‘l O E m It lL L/ UNCONFORMITY UNCONFORMITY UNC Hi _ W‘J auaaag ”39mm” Andeaite flow UNCONFORMITV 0 0 no .0 o..~’ “ /\7\ 1: /’\‘7\'>:‘/ \\\/\\|:\/l_\_ \ ’\\\’l\|\‘l\l I \ S. FIGURE 64.—Cenozoic geology of Last Ghance Canyon area, El Paso Moun 103 TERTIARY SEDIMENTARY AND VOLCANIC ROCKS dimes—02 8am an raw: £256 “Bow. 9:3 226: 53552 Mesa we 328w flosoneolfia 559% A AHVILHEJ. ‘38:! 1910f) A H V Ila 3 J. uopeuuog uogqmumg 09mm AHVNHELVDO ../. .o A % % # 3—99. )3 ‘5) baawfimvwmfiwz ((52. mumm 35552950 lo 00 a 32:53:00 0 .8... o £3qu «wank o N9_l_.+ £355: ism \ftszkZOUZD canoe .mp o .... a 30:5» >F;m._ (um boow boom 4m>m4 (mm boom .OOOV boom .OOON 4m>m4 (mm .OOON 4w>m4 (mm booN .OCON .88 C l /\< ,x/A\\/\ / l ,AOl/C/ I/ \///:,/\m, _ L \//\\\/ \4F .99 (mm 3.90 Nova/5 t /\\/\\/\_.m_u\\/\/\ WW \L.D/1 _/7\/_\_/ 1/\/ \ \ \ \ \ /I / )0 7O CHEF boom ha I. v 3 d 338 ww % 353920 Ha I. :oSwESm V 3 .530 .w._. Ma m. cots—Eek 4 852m .fi 0 fiamwm D 55582 w. x35 do 3 E335“ w 320 «co V ovzmwflmd ~£0 a _ A 5:322 no 4m>m4 (mm booN TERTIARY SEDIMZENTARY AND VOLCANIC ROCKS Mammalian fossils of Ricardo fauna found mostly in beds (members 6 and 7) above basalt flows, near Ricardo in Redrock Canyon, described by Merriam (1919, p. 525—529) and assigned by him to early Plio- cene (Clarendonian) age. Another mammalian fauna, and flora from beds (member 5) below Ricardo mam- malian fauna also believed to be Clarendonian in age. Ricardo Formation therefore considered to be early Pliocene of the mammalian time scale. LAVA MOUNTAINS AREA GRAY ANDESITE PROPHYRY Two exposures of gray andesite porphyry, one across US. Highway 395, 2 miles east of Summit Diggings (fig. 68) ; other 14—2 miles farther east (pl. 1). Rock intrusive, extrusive, or both. Apparently overlies quartz monzonite; in eastern exposure overlain by tufi' of Bedrock Spring Formation; in western exposure, porphyry wedges westward into it. Rock composed of scattered to numerous white phenocrysts of plagioclase (partly altered to sericite, albite, kaolinite, and calcite) and small black pheno- crysts of hornblende (largely altered to limonite) in dark-gray aphanitic groundmass. Rock probably same age as basal part of Bedrock Spring Formation, middle Pliocene, or possibly older. RHYOLITE 1‘aner Rhyolite felsite exposed in eastern Rand Mountains; just south of Johannesburg, felsite forms volcanic mass intrusive into quartz monzonite, flanked on northwest by rhyolite flow breccia extrusive on quartz monzonite; generally vertical dikes of felsite as much as 30 feet wide radiate from intrusive mass (fig. 3). At north end of Red Mountain, rhyolite felsite forms small volcanic plug with concentric flow laminae parallel to its vertical margin that is partly bordered by dark-gray vitrophyre. Plug either intrusive into or possibly buried by sandstone of Bedrock Spring Formation. F elsite white, gray white to cream white, rarely pink; weathers bufi' ; massive to faintly flow laminated, aphanitic to slightly porphyritic; composition pre- sumably ranging from rhyolite to quartz latite; according to Hulin (1925, p. 49—50) composed mainly of orthoclase and quartz, with minute amounts of muscovite, biotite, green hornblende, magnetite, and pyrite; contains scattered small phenocrysts mostly of orthoclase and quartz. Age relationship of rhyolite felsite to Bedrock Spring Formation controversial, as indicated by field relation of small plug at north end of Red Mountain. 105 Abundance of felsite dikes in pre-Tertiary rocks, their absence in Bedrock Spring Formation, and abundance of felsite fragments in Bedrock Spring Formation suggest felsite is older than that formation. Felsite therefore middle Pliocene or older, possibly Miocene, in age. BEDROCK SPRING FORMATION A sequence of fluviatile sedimentary and some pyro- clastic rocks of Pliocene age unconformable on Mesozoic quartz monzonite and overlain by andesitic volcanic rocks exposed in Lava Mountains, mostly beyond northeast border of mapped area; also exposed on slopes of Red Mountain and near Summit Diggings (pl. 1). Referred to Rosamond Series (of former usage) by Hulin (1925, p. 42—48, pl. 1); in Lava Mountains mapped and described in detail and named after Bedrock Spring by Smith (1964). Type section near Bedrock Spring in Lava Mountains, beyond northeast border of mapped area, where formation is as much as 5,000 feet thick. In Red Mountain area Bedrock Spring Formation probably about 5,000 feet or more thick; thins south- westward by onlapping against pre—Tertiary rocks as indicated from mine workings near town of Red Mountain; intruded by andesite (fig. 67). Sequence composed mostly of light-bufi' to locally green and red sandstone and lesser amounts of interbedded conglom- erate, green to red sil-tstone, and occasional bed of white tufl'. Pebbles of conglomerate mostly of gran- itic rocks, few of rhyolite felsite and of Rand Schist. Rhyolite breccia composed of angular fragments of tan rhyolite felsite. Near Garlock fault northeast of Summit Diggings, about 1,900 feet of strata referred to Bedrock Spring( ?) Formation exposed in anticline, but almost entire sequence onlaps( ?) against quartz monzonite to east (fig. 68) ; lowest 1,000 feet of formation composed of gray—white, green, and pink arkosic sandstone, some interbedded andesitic and granitic pebble-cobble con— glomerate, and green—gray to red siltstone; upper 900 feet, which may be basal part of andesite volcanic complex rather than Bedrock Spring Formation, com- posed of about 100 feet of bentonite and fine-grained bedded tufl’ which grades upward into about 800 feet of white coarser tufl' and lapilli—lithic tuff breccia. Mammalian fossil remains in Bedrock Spring For- mation in eastern Lava Mountains (4—6 miles east- northeast of Klinker Mountain) considered to be younger than Ricardo fauna, or probably middle Plio- cene of the mammalian time scale (G. E. Lewis in Smith, 1964, p. 21). 106 AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA v ;, ._ ,3“ Q“-§'~.../’ '22 R, 4] E. R, 42 E. r o . st/ Bedrock Spring Formation Alluvium V QUATERNARY Y TERTIARY W E] \ Older alluvium § UNCONFORMITY > § , '§ 0 o E o B o Fanglomerate UNCONFOPMITY [\A '—~'"‘_ 9 V ‘p‘ Intrusive Andesite and breccm extrusive and flows andesite — + + + \ \ Tuff breccia g Intrusive ‘ ,4 :1 I : rm “green" " v v A V andesxte Rhyolite felsite D l V V D A <7 Sand- Rhyolitic stone breccia UNCONFORMITV ‘ / \~ / 4000' \ , C315“ \ Quartz monzonite 2000' : ‘2. N W SEA LEVEL Rand Schist 4000' 2000' SEA LEVEL PRE—TERTIARY TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 107 R 40 E, R. 41 E. I ummit « - 'di in ' —— 4/ __ X_' E: s / .+ : -?‘: . . ., . EXPLANATION 9 a § 0 8"; Alluvium >. V [I - < Z é Terrace gravel ? 5 § < UNCONFORM/TV i; g D n. 0 , . — 4000' Older alluvmm Landslide rubble I (fanglomerate) of Garlock I Formation I h" UNCONFORMITY “I, —- 2000' V L\\\ SEA LEVEL Unnamed sandstone Basalt and conglomerate Intrusive and eztmu've >_ D! g s §< n '~ Andesite I: K m A '— 4000' $1 an E .5 g‘ d4 m g / 2000' .1 ,. . r2 Gray nndesxte porphyry L Sandstone / SEA LEVEL UNCONFORMIY‘V >. [I s Quartz monzonite Quartz diorite E LLI 'T m I! Garlock D. 0 1 2 MILES Formation l l I FIGURE 68.—Geologic map and sections of Summit Diggings area. 239—655 0— 67——-9 108 ANDESITE Porphyritic andesite of Pliocene age intrusive into and extrusive on Bedrock Spring Formation promi- nently exposed in Lava Mountains, Summit Diggings area, and Red Mountain (pl. 1). Mapped and described as Red Mountain Andesite by Hulin (1925, p. 55—58, pl. 1), but name no longer applied to this volcanic unit. In Lava Mountains, mapped in detail by Smith (1964). Andesite divided into three units (pl. 1), all grada- tional and not everywhere distinct: intrusive andesite, andesite breccias and flows and andesite flows. Andesite of all three units petrographically similar; unaltered andesite massive, porphyritic. Most pheno- crysts white, rectangular, of plagioclase (andesine, Anao—so), as much as 6 mm long; make up 10—30 per- cent of rock mass; other phenocrysts smaller, black prismatic, of hornblende (oxyhornblende) and pyrox- ene (clinopyroxene and orthopyroxene). Groundmass aphanitic, locally subvitreous, medium gray (Smith, 1964). In places andesite hydrothermally altered to propylite having phenocrysts of feldspar partly replaced by sericite, albite, and calcite and phenocrysts of ferromagnesium minerals replaced by sericite, cal- cite, epidote, chlorite, and opaque minerals (Smith, 1964). Intrusive andesite forms much of southern Lava Mountains and most of Red Mountain. This andesite generally massive but in places has indistinct frac- ture parting parallel to outer walls of intrusive masses. In Lava Mountains, intrusive andesite occurs as two main types: purple to brown andesite and green andesite, although there are intermediate types. In many places, partly to wholly altered to propylite (Smith, 1964). Purple to brown andesite ranges from purple through blue gray and pink gray to brown: forms irregular complex masses intrusive into and gradational into andesite breccias and flows. Green andesite ranges from olive green to olive brown; occurs as numerous parallel, nearly vertical merging dikes and pods that trend west of south from southern Lava Mountains into east slope of Red Mountain; intrusive into quartz monzonite and Bedrock Spring Formation (fig. 67). On Red Mountain, andesite intrusive through Bed- rock Spring Formation (fig. 67) ; lower parts of ande- site bodies olive green; upper parts olive to reddish brown; highest parts may be partly extrusive onto depositional surface of Bedrock Spring Formation as suggested by local brecciation of andesite near contact and by dip of contact inward toward intrusions. Andesite brecci-a and flows (Almond Mountain AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA Volcanics of Smith, 1964) exposed extensively in western and southern Lava Mountains; gradation‘al into associated intrusive andesite; overlie Bedrock Spring Formation, in places unconformably( ’9). Composed of mixture of irregular flows, flow breccia, and andesite cobble-boulder 'breccia or conglomerate; colors vary from purple to pink gray to brown. Lenses of pink and buff to white tufi', arkosic sandstone, and conglomerate, as much as 50 feet thick, present locally near base and near top; total thickness of ande- site unit unknown, but probably more than 1,000 feet, possibly 2,000 feet; unit locally hydrothermally altered. Andesite flows (Lava Mountains Andesite of Smith, 1964) in Lava Mountains occur as isolated flows as much as 100 feet thick of dark-brown to reddish-brown andesite that cap andesite breccias and flows in Klinker Mountain area, lap northward unconform- a‘bly(?) onto Bedrock Spring Formation (pl. 1). In Summit Diggings area, andesite rests on Bedrock Spring( ?) Formation, in places unconformably; may be as much as 300 feet thick; possibly in part intru- sive; ranges from dark brown to light gray to rusty brown. Overlain by unnamed sedimentary rocks and basalt to west (pl. 1; fig. 68). Andesite younger than middle Pliocene Bedrock Spring Formation that it intrudes and upon which it rests, and older than fanglomerate of probable Pleisto— cene age that unconformably overlies it (fig. 67), thus presumably late middle to late Pliocene age, most probably late Pliocene in age. UNNAMED SANDSTONE AND BASALT Sequence of sandstone and basalt, apparently over— lying andesite and unconformably overlain by Quater- nary fanglomerate, exposed between Summit Diggings and Garlock fault. Sandstone included by Hulin (1925, p. 58—60, pl. 17, pl. 1) in Rosamond Series of former usage and basalt described and mapped by him as Black Mountain Basalt. Sequence and structure of formation shown on fig- ure 68. Formation about 1,800 feet thick; lowest 700 feet indistinctly bedded friable light-buff arkosic sand- stone, in places containing pebbles of granitic rock and rhyolitic felsite; includes local lenses of gray to red micaceous siltstone. Overlain by flow (or sill?) of weathered basalt having possible maximum thickness of 500 feet, thinning northeastward; presumably flowed from vent now filled with plug of hard basalt two- thirds of a mile north of Summit Diggings; basalt microcrystalline, composed of lath-shaped feldspars, magnetite, and glass; contains scattered phenocrysts of plagioclase (labradorite—bytownite), brown horn- QUATERNARY SEDIMENTARY DEPOSITS AND BASALT blende (partly replaced by magnetite), and augite (Hulin, 1925, p. 60). Basalt overlain by about 900 feet of buff arkosic sandstone that forms uppermost part of formation; in- cludes some thin intercalations of micaceous shale, somewhat siliceous, in exposure three—fourths of a mile N. 30° W. of Summit Diggings; in exposures west of Summit Diggings, lowest 300 feet of very hard thick— bedded sandstone that forms resistant ledges; rest of sandstone soft and friable. No fossils found in formation. Presumably late Pliocene in age, younger than andesite and older than unconformably overlying fanglomerate of Quater— nary age. QUATERNARY SEDIMENTARY DEPOSITS AND BASALT OLDER ALLUVIUM Older alluvium, presumably of Pleistocene age, com- posed of semiconsolidated fanglomerate, gravel, sand, silt, and clay, underlies much of Mojave Desert. As much as 1,000 feet or more thick; presumably underlies Recent alluvium of all valley areas. Exposed and dissected in former valley areas slightly elevated by late Quaternary crustal movements. In Mojave Desert between Rosamond and Barstow areas, fanglomerate (pl. 1) in part underlies and there- fore in part older than remainder of older alluvium; as much as 600 feet or more thick. In exposures be- tween Rosamond and Hinkley, fanglomerate composed of unsorted boulders and cobbles mostly of granitic rocks. In exposures southeast of Mojave River, fan- glomerate composed of cobbles derived from Mesozoic plutonic rocks and porphyry complex. At Red Moun- tain, fanglomerate composed of andesite detritus. Re- mainder of older alluvium, as much as 700 feet thick, composed of gravel and sand derived from nearby ex- posures of pre-Tertiary and Tertiary rocks. North of Hinkley includes some lacustrine clay and marl. Along southern margin of Mojave Desert and Cajon Pass, older alluvium forms dissected north-sloping piedmont alluvial fan that was elevated by northward tilt and beheaded by Cajon Creek drainage system (pl. 1, figs. 31, 32, 33). Older alluvium of this area conformable on Crowder Formation where present, lapping onto pre-Tertiary rocks; about 1,000 feet thick; composed of coarse gravel derived from plutonic rocks, gneissic rocks, and Pelona Schist of San Gabriel and San Bernardino Mountains. In large part mapped by Noble (1954a, 1954b) as Shoemaker Gravel. In Cajon Pass area lower 300 feet (figs. 31, 32) composed of greenish-gray finer gravel, sand, and silt. In San Gabriel Mountain foothill area westward from Valyermo, older alluvium unconformable on Ter— 109 tiary and pre-Tertiary rocks; as much as 400 feet thick; composed of coarse gravel; in' places lower part com- posed of greenish-gray finer gravel, sand, and silt (included in Harold Formation as mapped by Noble, 1953, 1954b) as in Cajon Pass area. Two distinct facies mapped (pl. 1, figs. 27, 28, 29) : gravel of mostly granitic detritus, and gravel of mostly Pelona Schist detritus (northeast of San Andreas fault in part mapped by Noble, 1953, as Nadeau Gravel). In Tehachapi Mountain foothills, older alluvium as much as 1,000 feet thick where exposed by crustal move- ments and dissection; upper part, as much as 400 feet thick, is coarse gravel; lower part, as much as 500 feet thick, is finer gravel and interbedded reddish- to greenish-gray silt and gray to bufl' sand; exposed only locally (figs. 69, 12, 62). Terrace gravel, present as erosional remnants (pl. 1) , deposited on erosion surface cut into older alluvium and older formations. In Cajon Pass area (fig. 31), terrace gravel south of Horsethief Canyon composed of Pelona Schist detritus. Three deposits southwest of Cajon Creek are landslide debris of quartz diorite and gneissic rocks. Older alluvium generally unconformable on forma- tions of Pliocene age and underlie Recent alluvium, therefore most if not all of older alluvium probably Pleistocene in age. In places lowermost beds may extend down into very late Pliocene. BLACK MOUNTAIN BASALT Basalt presumably of Pleistocene age exposed over wide area as a thin sheet of one or more lava flows less than a total of 100 feet thick on Black Mountain north of El Paso Mountains (pl. 1). Overlies Ricardo Formation with no visible discordance; farther east lies on Goler Formation ('fig. 26). Basalt of this area named by Baker (1912) ; mapped by Dibblee(1952), p. 30, pl. 1), and name oflicially adopted for use in this report. Also exposed on Black Mountain southwest of Opal Mountain, and east of Opal Mountain (pl. 1; figs. 65, 69). In both these areas basalt sheet as much as 150 feet thick; thins out in all directions, in one place into older alluvium; overlies beveled surface of Barstow and Pickhandle Formations; laps eastward onto Meso- zoic quartz monzonite and Lane Mountain Andesite; in part deformed, elevated, and dissected. Basalt pene— trated by several test holes in Harper Valley. Basalt black, hard, fresh, vesicular, very fine grained, ophitic; composed mostly of plagioclase (labradorite), pyroxene, and small amounts of olivine and iron oxides. Black Mountain Basalt presumably of Pleistocene age, as indicated by (1) unconformable relationship on formations of Tertiary age as young as Pliocene. 110 R. 15 W. AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA EXPLANATION 3970’ Alluvium Windblown sand 0 :- Meridian Oil - a o Co . ‘ o ‘ ° ~° o~3300¢ sandy . sediments Alilavml sailid 3300’-3970’ quartz a ave diorite .. . QUATERNARY 1 4 . Clay and silt Older alluvium Arkosic sand / / _ Granitic basement ‘ MESOZOIC (.7) 2000' I 4000’ " 2000' 1 MILE SEA LEVEL SEA LEVEL FIGURE 69.—Geologic map and section of Sand Hills. (2) lensing out into gravel of older alluvium 5 miles east of Opal Mountain, and (3) preservation of top surface of lava flow throughout most exposures. ALLUVIUM Generally undissected alluvium of Recent and pos- sibly very late Pleistocene age covers desert valleys and flood plains of all streamcut valleys and canyons within mapped area. As much as 100 feet thick; in broad desert valleys gradational downward into older allu- vium; elsewhere unconformable on older alluvium and on all older formations. Alluvium composed of unconsolidated detrital sedi- ments derived from adjacent highland areas; follow- ing facies of alluvium recognized, all gradational into each other: fan alluvium, valley alluvium, river sand, and sand bars. Fan alluvium forms alluvial fans of coarse detritus deposited at foot of mountains and hills; composed of fanglomerate, gravel, and coarse sand of angular to subrounded fragments as large as several feet; extends far up flood plains of canyons; top surface slopes as much as 500 feet per mile. Fan alluvium grades downslope into valley alluvium of broad desert plains and valley; composed of grav- elly sand, sand, sandy silt, and clay; deposited by streams as outwash from alluvial fans; top surface nearly level, slopes 5—200 feet per mile. River sand fills stream channels of Mojave River and some channels of larger washes; sand well sorted, medium to fine. Deposited by ephemeral streams that flow only for several days, weeks, or months each year. Around and near margins of large playa lakes, val- ley alluvium locally covered with thin, elongate bars of coarse- to medium-grained sand parallel and con- centric to margin of playas; these are sand bars evi- dently deposited by wavesalong shorelines of receding ancient lakes that once filled these lowland areas. GEOLOGIC STRUCTURE WINDBLOWN SAND Loose bufi' well-sorted fine-grained sand deposited by prevailing westerly winds in form of closely spaced dunes or thin cover on many parts of desert (pl. 1). Windblown sand most extensive on east margin of Antelope Valley; forms numerous dunes between Rosa- mond and Rogers Lakes, some dunes forming rims around east side of small playa lakes; forms extensive veneer on broad west slope of low hills east of Rogers Lake. East of Harper Lake, sand forms irregular dunes; elsewhere sand forms thin surface layer. PLAYA CLAY Clay or mud forms level floor of existing playa lakes in lowest parts of undrained desert valleys; clay gray, finely micaceous; generally alkaline, especially on larger playas where mostly sodium carbonate and so- dium chloride cover playa surface after evaporation of saline water following infrequent heavy rains; clay of Koehn Lake highly alkaline. Pl-ayas devoid of vegetation owing to alkalinity of clay. Clay soft and pliable when wet, firm when dry. GEOLOGIC STRUCTURE The major structural features of the western Mojave Desert are shown on plate 1; structural details of areas Within it are shown on the figures throughout the sectibn “Rock units.” The basement complex of pre-Tertiary crystalline rock-s of the Mojave block and adjacent areas is mainly a granitoid batholith, presumably the southern exten- sion of the Sierra Nevada batholith that is generally devoid of discernible structure. It contains isolated unassimilated remnants of intensely deformed meta— morphic rocks (pl. 1). The dominant Cenozoic tectonic features of the Mo- j ave block are the high-angle San Andreas and Garlock faults which bound it (pl. 1) and along which moun- tain ranges were elevated. The fact that high-angle major faults within the block are generally parallel to these master faults suggests that they are genetically related. TERTIARY DEPOSITIONAL BASINS The Cenozoic structure of the Mojave block consists of large elevated areas of basement complex separated by extensive valley areas or basins filled with Ceno- zoic deposits. The Tertiary formations that overlie the basement complex as erosional remnants on the ele- vated areas are much deformed by tilting, folding, and faulting. Structural trends of fold axes in Tertiary rocks throughout the western Mojave Desert are gen- 111 erally eastward. Quaternary deposits that cover the basins and lap onto the eroded surface of Tertiary and basement rocks of the elevated areas are themselves locally deformed in the same manner, mostly near faults, but to a much lesser degree (pl. 1). In the basins, Cenozoic deposits extend to depths of several thousand feet as indicated from logs of some deep test holes (table 4). In order to shed light on the probable areal extent and configuration of the basins filled with Cenozoic deposits, which are low-density materials as compared to the pre—Tertiary crystalline rocks, a gravity geo- physical survey was made of the entire area by Mabey (1960). His report includes a gravity map as well as a detailed description and interpretation of the gravity variations. Figure 70 shows the gravity variations generalized after Mabey (1960, pl. 10). Figure 71 shows the prob- able areal extent of basins filled with Tertiary deposits, based upon their known outcrop distribution, their probable concealed areal extent as inferred from the gravity data shown onfigure 70, and from logs of several test holes. Figure 71 also shows probable pro- files across the major basins shown, based on interpre- tations of the gravity data by Mabey (1960). From figure 71 it may be noted that most of the depo sitional basins are elongated generally eastward. The large areas of basement complex that separate the basins were probably in large part highlands that Were elevated as the basins were depressed; if so, they must have shed detritus into the basins during Tertiary time. This condition is suggested by the great difference in the sequence in each basin and by the coarsening of some formations toward the basin margins. The local sequences shown on plate 4 were deposited in the basins shown on figure 71 as indicated on that plate. FAULTS The San Andreas fault, which forms a straight trenchlike feature bearing about N. 65° W. through the mountains and hills along the southwest margin of the western Mojave Desert, is a vertical shear zone of gouge and crushed rock a few tens to several hundred feet wide. Parts of this 90-mile segment are described in detail by Noble (1953, 1954a, b, p. 44-66), Wallace (1949, p. 7 92—797), and Crowell (1952, p. 18—20). The fault is highly active as indicated by recently formed scarps, shutter ridges, sag—ponds, offset stream chan- nels, and small ridges. All these features indicate active right-lateral or horizontal southeastward move— ment of the northeastern side relative to the south- western side. Other parallel faults such as the Punch- bowl and Nadeau faults are less active but have the .112 EXPLANATION E 53 '2; N D Alluvial sediments and basalt o >. m }5 I- I Sedimentary and volcanic rocks E Plutonic and metunorphic rocks W PRE- TERTlARY 900 995 Gravity contours Contour interval 5 milliauls. Gravity value: are complete Bouguer anomaly plug 1000 milliaal: 20 MILES AREAL GEOLOGY, WESTERN MOJAVE DESERT, CALIFORNIA FIGURE 70.-—Bouguer anomaly and generalized geologic map of western Mojave Desert. Gravity anomaly contours after Mabey (1960). same type of displacement and are part of the San Andreas fault zone. The older alluvium is everywhere truncated, dis- plaeed, and locally folded by lateral movements on the San Andreas fault. Old dissected piedmont fans on the northeast side of the fault, derived from moun- tains southwest of it, are generally displaced south- eastward from their source. The most striking exam- ple of this shift is the older alluvium composed of Pelona Schist detritus present as erosional remnants of a piedmont fan on the northeast side of the San Andreas fault between Palmdale Reservoir and Little Rock Creek. This older alluvium must have been de- posited at the northeastern base of the Pelona Schist exposure of Sierra Pelona from which it was derived (pl. 1). It is displaced by right lateral movement on the fault about 7 miles southeast and is now adjacent to older alluvium of granitic detritus across the fault (figs. 27, 28). Cumulative right-lateral displacement on the San Andreas fault zone since early Pliocene time may have been as much as 40 miles, as suggested on figure 72. The Garlock fault is a northeast—trending zone of high-angle faults along which movements have been GEOLOGIC STRUCTURE 113 lo 20 MlLEs EXPLANATION vzwncu. sen: ls mm: , THE HORIZONTAL SCALE n: m secnons E “E , 2“ Alluvial sediments and basalt 32 >. I m 5 - E Sedimentary and volcanic rocks II.l_l > n: I n: . . ‘ . ‘ 1'5: - ~ - . .. ~ thmic and metamorphic rocks :5 4‘ . ' . - 1 , ' . ' k . .‘ , . . 9.6 <>— - . _’ . ',';',6p:' ‘. , y ‘16.- ------- - Inferred limit of depositional F) “03:52 buin .— z” 80 l HM \ :ARSTO Axis of basin on downwarp - . n . Fault Dotted when concealed w Bonnie deposit X Mine ¢. Test well * SEA LEVEL 10,000' SEA LEVEL . 10,000' FIGURE 71.—Probable areal extent of depositional basins filled with sedimentary and volcanic rocks of Tertiary age in western Mojave Desert, and their inferred profiles and depth, as based on surface exposures, gravity data, and data from test wells shown. 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