UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.35 (National version of master negative storage number: CU SN03067.35) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of “fair use," that user may be liable for copyright infringement. University of California at Berkeley reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. Lloyd, H. B. A geologic study of a portion of San Pablo Valley 1923 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.35 (national version of the master negative storage number: CU SNO03067.35) GLADIS NUMBER: 184787247F FORMAT : BK AD:991009/FZB LEVEL:b BLT:am DCF:a CSC:d MOD: EL: 7 UD:030604 /MAP CP: cau L:eng INT: GPC: BIO: FIC: CON: ARCV: PC:S PD:1923/ REP: CPI: FSI: ILC: ITI:0 CUScCU SbDISS.LLOYD.GEOL 1923 1 Lloyd, H. B. 12 A geologic study of a portion of San Pablo Valley, Scl923. 23 p. :Sbcol. i111, maps ;$c29 cm. Thesis (B.A. in geology)-- University of California, Berkeley, December, 1923. 20 University of California, Berkeley.S$bDept. of Geology and GeophysicsSxDissertations. 0 Dissertations, Academic$xUCBS$xGeologyS$y1921-1930 Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X PM-1 3%."x4” PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT 10 Be 2 p— ss [ll 3.2 = plz Is w fl Bes l TE = hi ee ° = hk l= E22 lis pe AM : ol ly gl lp ql, Is) ly 1g - | | ” o J 9 a b ge 2 r- eubiL et ot toot le 18 12 10 IEE 8 Ll ful i INTRODUCTION wir se non em mim sm sion a ne ini se rm 20 so a i rm i sin sm en 4 }72 3 : location and Extent-scssscccmmmmmcncnccccrccccnnccnsnmsnnnasnsneas eA! Acknowledgements ~~eececececcncacnmmmcmmcnnccncccccnncccnncn cae 4 Nature of Problem and Field Methods ~-cemcccceccccccacaaa- —— 5 GENERAL FEATURES ececcemcccccccccacccncmmeccccncnccccncsccnssccnananns 6 A GEOLOGIC STUDY OF A PORTION OF SAN PABLO VALLEY CUinntE and Voratalion weve esesamssssrmmsssnmssssasni animate 6 Culture and Accessibility =eeecccccmm mmc 6 BY H.B. Lloyd Topography =eeececm meme eee eee ee 6 Lo. Drainage ==eccececcceccmcammm cnn ccmcac cnn ccc cere cn meen ene ———— 7 A LIBRARY COPY GEOLOGY wow conn cnnmmmmismmntsessaamcamsvs mmm eres researc atoc arma 7 : General Statelenl =wiossccmsasaceccnmrarmssnnensaeenn en. nome—e—- 7 J ¢ In fulfillment of the Thesis Requirement for the degree of Bachelor Igneous RoGkS mee=svesssmueus mem —————————ye 8 of Arts in the College of Letters and Science,department of Geology Weathering =srasnesssnssesmsssarevnupuvevssvesserearanesezanens n 5 Salvirstts of Lalifiriin: Spheroidal Basalts m-mmmmsmmmmemmmmsmesmmmmssmmemmeenans —- 12 Laterites =ceccccncaceccccccccccccccccee vem 12 Submitted : Sedimentary Rocks ~cecccccacccccanccncaccccrcnncccrcccececcccnnce 16 December 11,1923. : Structures --cecccccccccccccccc cc cne ence c rece cnc cece cena ae 18 Age of Formations ececcccccecccccccccccncccccccacccncccccccacencces 19 Geologic History e=eeccmcmccccccecccccccnccncc ccc rerccccccccnnane 20 ECONOMIC POSSIBILITIES wececccmccccccnmne meen eee ——e———————————— 21 Limestone eeccecmccccncrccccccnrccnncccccrcssrccnccecccccecenensee =e slope i form SO uni al runs, NCW HR r a > = aa QO z oO aw 3 a all i O 2 < = 2 INTRODUCTION Location and Extent of the Areas= This report describes the Geology of an area three miles square,in San Pablo Valley,Contra Costa County,California. The area was so chosen as to give the greatest amount of structure and variety of rocks in a small unit. The southwestern limit of the map is approximately parallel to the ridge which trends about S.45 deg.E. from Eurekm Peak and which in general is parallel to the strike of the region. Acknowledgementss= Thies region has previously been mapped on a small scale,with little 1 . reference to detail by A.C.Lawson . The age relationships of the different formations were obtained from the above folio. Detailed work has been done in the region immediately to the southwest in a portion of the Berkeley Hills,by A.Celawson and Charles Sandie n Mapping work has been expediated greatly by the assistance of N.M.Erskine,who also id working a Thesis in this ares. Much credit must be given and appreciation expressed to Dr.R.R.llorse who has offered many valuable suggestions and aided in various ways the progress of the work. Nature of Problem and Field Methods:- Some explanation of the purpose,the method of attack,the amount,detail, and accuracy with which the work in this area was done is considered to be of value for a proper understanding of what follows. The original intent was to make a detailed geologic survey of an l.Lawson,A.C. San Francisco Folio No.193.Geologic Atlas of the United States, UeSeGeSe 2+A.C.Lawson and Charles Palache-Geology of a Portion of the Berkeley Hills Bull «Dept.of Geol .Univ.of Cal. Ve2.pp. 49-451. area which has previously been mapped on a small scale by the United States Geological Survey,giving a petrographic report on every variety of igneous or sedimentary rock in the region,and tomake a microscopic analysis of the various sedimentary members in the hope that the data so obtained,would serve as a check upon conditions of deposition as have been inferred from paleontological evidence. It was found,however,that the accurate detailed mapping of the region presented more difficulties than had been anticipated, due principally to the inexperience of the author in field work,and also to the difficulty in locating the contacts which in many cases are covered with a heavy mantle of vegatation. With a limited amount of time available for the work, the problem has been confined chiefly to an areal and structural study. The purpose of the work was essentially to secure the field experience 80 necessary for the successfull prosecution of geological studies,and incidentially to fulfillthe requirment for the degree of Bachelor of Arts. The amount of work done in the area has been excessive in view of the results accomplished,but a great deal of experience has been gained. Twenty one days over a period of three monthe have'been spent in the field, eix of which were strictly reconnaissance surveys to become acquainted with the area. The original topographic map,being on such a emall scale was found to be extremely inefficient for detailed work,in consequence a new map was prepared,retaining the U.S.G.S. horizontal and vertical control but emphasing the topographic features for mapping purposes,and placing the new culture upon the map. This work hae all the accuracy which is possible with the instruments used,Brunton Compass,Barometer,and pacing. All contacts were then located by intersection from two or more points. GENERAL FEATURES Climate and Vegatations= The prevailing climatic conditions are similar to those of the interior valleys of California,the fogs of the coastal region rarely extending beyong Eureka Peak. The hill slopes and valley regions are covered with wild grasses and minor amounts of brush,the only native trees in the area are to be found growing in the canyons and are principally scrub oaks. Culture and Accessibility:= The ares ie readily accessible being but a matter of six miles over excellent trails,from the University Campus and a distance of twelve miles from tie city of Oakland over paved highway. Real estate promotion has been extended to include a greater portien of this area and the region is now being subdivided into tracte and lots, new roads and paths are now in the process of construction,and a great deal of exploration is being conducted to supply the future town of Orinda with water. Topography: = The most prominent topographic feature of the region is Eureka Peak, which has an altitude of 1625 feet,and constitutes the highest portion of a ridge which trends northwest and southeast. Sean Pablo Creek approx- imately paralleling the ridge has created a broad valley in which the towns of Orinda and Bryant are situated. To the north and east of San Pablo Creek the slope is more gentle and rises to an altitude of 900 feet within the limits of the map. Drainage:- The region being one of late maturity, the trellis type of drainage pattern is well developed and we find the tributary streams draining into San Pablo Creek at approximate right angles. These numerous ephemeral streams carry water only during the wet season, but during this period are very active and possees great erosive powers. A great portion of the raine fall on the northeast slope of Eureka Peak ridge goes into the run-off, due to the steep slope and the impervious nature of the underlying rocks; but on the northeast side of San Pablo Valley,the greater porosity of the rocks and their structural relations,and the more gentle slope,all combine to aid much of the rainfall to be absorbed,in consequence thie formation is an excellent water carrier. GEOLOGY General Statements In the region described by this paper are to be found many varieties of rocks both igneous and sedimentary. The geologic history of the region is varied including records of deposition, erosion,diastrophism,and volcanic eruptions. The geologic structure,while not comparable in magnetude is ways similar in many to that of the Berkeley Hills-folding and faulting being a common feature The oldest formations encountered within the limits of the map are the Monterey Groop(Miocene) - resting unconformably upon which are the fresh water Orindin(Pliocene) sediments. The Moraga (Pliocene) directly overlies the Orindin and ie the youngest member ofcurring in the area. Igneous Rockss- The several lava flows of the region are exceedinly difficult to Note- Irregular line crossing the plates a result of broken negative Crossed nicols- Olovine phenocryst in center in a groundmass of Bytownite feldspars. Note- arrangement of feldspare long direction in nearly the same zone. Basalt Same section as above with parallel nicols (8) (9) differentiate megascopically,the color,texture,and mineral constituents being very similar owing to the fact that they are all surface flows of & basic character. Examination of the rocks with the microscope,however, gives good evidence for differentiating between the flows. It wae found upon examination of the specimens collected from a single flow that some differentiation existed from top to bottom, so in making the collections for the purpose of numbering the fifferent flows the specimens were taken from near the bottom of the flow in all cases. A more complete report on the various lava flows in the region is forth- coming in the Thesis of Mr.N.M.Erskine. The only two types of igneous which were megascopically distinguishable in the field were the basalts and the andesites,and a contact between these two unite was traced in the field. Basalts of the type which occurr on the top of Eureka Peak,consist in the main of plagioclase,augite and olovine,with minor accessories of glass,apatite,and magnetite. The olovine occurs quite abundantly in the basalts and ite characteristic occurence together with the finer texture of the basalt serve as the distinguishing feature for thie flow. In thin sections the felfispar microlites usually exhibit polysynthetic albite twinning striations and are prismatic lath like in occurrence( See microphotograph on page ). The extinction angles measured on these microlites are the basis upon which the plagioclase feldspar is classified as bytownite. The texture of the rock ie fine grained microcrystalline,with occas- ional phenocrysts of olovine and augite,which are about twice the size of the feldspar constituents. A fluidal arrangement of the plagioclases having their long directions in approximately the same zone,give evidence of flow structure in the basalt(clearly shown in photograph). AT A + ANN Vv Trreriilar 13m mw, . €= lrreguiar line croesing 5 Yr man wm em A 2 the plates a result of broken negative RETAKE OF PRECEDING FRAME ( 2 -r ) (9) differentiate megascopically,the color,texture,and mineral constituents being very similar owing to the fact that they are all surface flows of & basic character. Examination of the rocks with the microscope,however, gives good evidence for differentiating between the flows. It was found upon examination of the specimens collected from a single flow that some differentiation existed from top to bottom,so in making the collections for the purpose of numbering the #ifferent flows the specimens were taken from near the bottom of the flow in all cases. A more complete report on the various lave flows in the region is forth- coming in the Thesis of Mr.N.M.Erskine. The only two types of igneous which were megascopically distinguishable in the field were the basalts and the andesites,and a contact between these two unite was traced in the field. Basalts of the type which oceurr on the top of Eureka Peak,consist in the main of Plagioclase,augite and olovine,with minor accessories of glass,apatite,and magnetite. The olovine occurs quite abundantly in the basalts and ite characteristic occurence together with the finer texture of the basalt serve as the distinguishing feature for this flow. In thin sections the felfspar microlites usually exhibit polysynthetic albite twinning striations and are prismatic lath like in occurrence( See microphotograph on page ). The extinction angles measured on these microlites are the basis upon which the plagioclase feldspar ies classified as bytownite. The texture of the rock ie fine grained microcrystalline,with occas- ional phenocrysts of olovine and augite,which are about twice the size of the feldspar constituents. A fluidal arrangement of the plagioclases having their long directione in approximately the same zone,give evidence of flow structure in the basalt(clearly shown in photograph). i a (10) (11) Note= Irregular line crossing plates due to a fractured negative. Immediately underlying the basalt occurs the andesite,which is coarser textured in appearance,and contains larger phenocrysts of plagioclase and augite than the above rock,olovine is noticeably absent,and the apparant flow structure of the basalt is not quite so readily observe in the andesite. The extinction anglee of the feldspars,35 degress(statistical method) classify them as labradorite. The phenocrysts occur in a finer groundmass of smaller plagioclases,augite and glaee,with minor accessories of apatite and magnetite. The basal member of these flows ie known as the ye isl endesite, end is characterized by smygdules of chert and chalcedony occuring in the vesicles,which resulted from the rapid cooling of the surface flow of lave. The rapid escape of stesm end gases from a cooling mess of lave results in the formation of a vieicular texture which offers an easy means of travel for the later circulating waters. These waters often carry a Andesite " frosses Mule DE El nt ns Ee ite. considerable amount of silica in solution,which is deposited in the vesicles as chalcedony or chert,thus giving us the present structure of the emygdaleidal andesite. In the weathering of this formation the chalcedony amygdules prove to. be more resistent and less easily broken down than the main mass of feldepar and augite,in consequence the alluvium covering this formation often contains a great number of these rounded chert and chalcedony pieces, which upon first examination of the ground give the appearance of having been derived from an alluvial wash. Weathering: -- Weathering processes have been going on so rapidly in this region ae to cause an accumulation of alluvium which erosional processes have been unable to remove, in consequence a heavy regolith now covers the region. Andesite Same section as above with parallel nicols RETAKE OF PRECEDING FRAME Immediately underlying the basalt occu t i A 3 textured in appearance,and contains larger the above ructure of the inction angles classify them ae smaller plagiocls anc magnetite, 4 FUT veo aed ad ge 4 nore resisient £ rite. Iv Ar = g " ~ 3 ; euglite, in consequence the alluviur covering thie Weatheriry ae to cause an ascounu 3 gli § processes have v1. urs \J the andesite,which is coarser phenocrysts of plagioclase and Aa ock.olovine 3 td pac TY « Hh - 2 4 rock,clovii noticeably absent,and the apparant 3 : - 1 > basalt quite so readily observe in andesite. s degrees( stati . LAA iy pCCur in - hp ~ 2 yn an edony occuring al Fis Ce Plow ~ vaters ie depc the vesicles A ent structure of the emygdelcidal emygdules prove lese es of formetion i ~~ A oad eo rounaes chert and cl ELC edony v . i eces J 1 s ia Vi I.g “2 give ihe appearence cf been going on sc rapi 4 2 A. 1 . od wr bo - po 3 3 } Lion of slluviunm which erosional processes nave -onseguence a neavy regolith now covers the region, ( 12) A very striking phase of rock weathering to be observed in the ares ie the spheroidal weathering of the basalts. The combined effects of the joints and additional parting planes hae first tended to separate the rock mass into more or less perfect squared blocks. Water percolating downward along the joints and laterally along the parting planes has subjected the entire surface of each block to‘ simultaneous attack by its reagents. Though all parts of the surface of each block are alike subject to attack,it ie the cornners and angles which are most vigorously acted upon. The minerals newly formed by those chemical proceeses of hydraticn and carbonization are noteably lighter and hence more bulky than the minerals from whose constituents they have been derived. Straine were thus set up which tended to separate the bulkier new material from the core of unaltered rock below. Eventually the squared block was by this process transformed into a spheroidal core of unaltered rock, wrapped in layers of the decomposed material,like the skin of an onion. These outer layers in many cases have much the appearance of a sedimentary rock. A complex and interesting rock alteration of laterite occurs in the Morsge,and as the nature of its occurrence warrents a little discussion the sence in which the term ies used will aid the the reader in following the writers description. The term laterite hase in thepast been vagely used,and as employed by different writers it has meant different things. It has been applied to ferrugineous clays, sedimente, beds of iron ore,and producte of volcanic action, but as the word was originally intended to describe a peculiar variety of rock,irrespective of its age or origin,for which & new name would have to be adopted if the familiar one were Standoned att is the lithological sense of theword which is here used. (13) The laterite in thie particular ares is brick red in color and when dry very firmly indurated, very much resembling an artificial brick,how- ever when the rock hae been washed or placed in water for some time it looses its hard resistent nature,and the water soon becomes a very red coler due te fine brick red matérial in suspension. Examined under the hand lens the rock has a very massive appearance, end shows very few distinct grains,an occasional feldspathic prism being observed which has not yet been completely decomposed. Evidence of strat- ification,or rounded sand grains is completely lacking,end it occurs as a distinct formation, varying in thickness from one foot to five between the andesite Flows. In some excellent exposures on road cute the laterite may be seen resting in clean cut contact upon what is known as the amygdaeloidal andesite,the upper contact being somewhat irregular and suggestive of an erosion -surface upon which the upper lava flow was poured. In this particular area there is no appearance of a gradation of the laterite into the underlying emygdaloidel andesite. On the south slope of the Berkeley Hills,however,the contact #s not quite eo distinct and a grad- ation may exist. The origin of laterites is an open question to account for which several hypothesises have been advanced. (1) Alteration from ferrugenous deposits of lacustrine origin.(2) Alteration "in situ" from the deriving igneous reck,the rock having been altered by the action of surface waters, (3) Alteration "in situ" from a distinct and separate lava flow which Was more susceptable to laterization than the others. Mr. F.ReMallet in examining the ferruginous which are interstratified with the volcanic rocks of tisler sigzents that the laterite is of lacustrine origin. During the decay of vegatable matter in the presence R.D.0ldham -Geology of India 2nd.Edition page 385 1 Records xiv, 139 (1881) (14) of higher oxides of iron,oxygen is absorbed, reducing them to protoxide,which unites with carbonic acid,a product of the decomposition of vegatation, to form ferrous carbonate, soluble in water containg an excees of carbonic acid. When water carrying this ferrugineous carbonate in solution is exposed to the air in etresms and lakes it absorbes oxygen. The ferrug= inous carbonate is decomposed with the escape of carbonic acid and a re= oxidation of the ferrous oxide into insoluble ferric oxide,which is pre- cipitated wherever the water comes to rest in a lake or marsh. That this deposit is of origin similar to the above hardly seems possible in view of the fact that there is a lack confirmitory evidence such as stratification, rounded send grains,or presence of other sedimentary material immediately above or below the laterite. The hypotheeis that the laterite is an alteration in place of the under- lying andesite is a possible solution of the question. Supporting evidence for such a statement might be the apparent gradation of the laterite into the underlying amygdaloidal andeesite,which evidence,however is entirely lacking in the area under discussion. The clean cut contact observed in road cute is difficult to explaincon any such basis. In localities where the contact is not so sharp,as on the south slope of the Berkeley Hills, the apparant gradation may be due toinfiltrations of iron comming from above which effected the surface of the andesite beneath. That the laterite is an alteration "in situ" from separate,distinct lava flow,whichwas more susceptable to laterization,due possibly to a higher percentage of iron containing minerals,is a very plausable hypothesis. A lave flow rich in iron and existing under conditions which favored the concentration of iron and the removal of some of the other constituents, would give just such a lateritic accumulation,with sharp contacte in many Cases,and in others a more indistinct contact due to infiltrations into the underlying mass. “uc aC - Sas damp. a "nom s y Lio Luc ITEJEUD . . 'POOR IMPRINT RETAKE OF PRECEDING FRAME herty limestone. rr or Sedimentary Rocks: The sedimentary rocke in the area consist in the main of sandstones both lacustrine and fluvatile, conglomeratic phases of the same,shales, tuffs,lignite beds of very minor extent,limestone lenses,and clays. The occurrence of limestone between lava beds is found in the Orindin. The formation in itself is of little value being of an impure nature, containing a great deal of chert,and varying in width greatly. The maximum width being about 4@ feet,and grading down in places to a width of 1 foot. Thepresence of this limestone between two lava flowe is indicative of the fact that a long period of time must have elapsed between periods of volcanic activity,periods during which sedimentation progressed at a uniform rate,and under fairly quite conditions. The limestone is of fresh water origin,end probabally accumulated in a large freeh water lake, for many fresh water ostracods are to be found imbedded in the limestone. The lacustral basin is some what indiceted by the strike of the beds, which as seen from the accompanying map trend more and more to the east as you pase from Eureka Peak to the east. between In the long periods of time intervening conditione of volcanic activity, sedimentation wae going on at a uniform rate as is to be inferred from the accumulations of sandstone, enidgtometaten;limgetines ind shales,which are to be found in the midst of the lava flows. In these intravolcania sedimentary accumulations are also to be found very narrow beds of lignite which lens out rapidly associated with fairly consistent layers of shale and clay. The shales which occur near the top of the Orindin are banded and exhibit a fine laminated structure which is furthur emphasised bg a color contrast,alternations of fine dark bands with lighter gray ones. (17) The regularity of these bande their presistence,and repgtition,give a series which may be paired off. The darker bands are as a rule,the narrower and often have a width not greater than a pencil line,while the lighter colored bands vary considerably from an eigth of an inch to about a thirty seconth of an inch. The dark color of these bands is presumably due to the decomposition of organic material,and possibly represents that accumulation which took place during the season of little rain,while the lighter bande being wider and having an absence of a noticeable amount of organic discoloration, probabally accumulated much more rapidly,and under conditions in which the water carried a great deal of material in suspension. In consequence of this condition,these bands would be wider,and freerer from discaloration , assuming the amount of organic material supplied to the streams to remain fairly constant. These paired bands,then are possibly results of seasonal variation. An exceptionally broad dark band paired with a narrower light band having accumulated during a seasom of less rainfall than the normal season. The tuffs interstratified and mixed with the sandstones are evidence of the activity of some distant volcanoe,which emitted a great deal of very fine ash that was carried in the atmosphere for considerable distances, finally settling out into well sorted and stratified beds. The tuffs mixed with the sandstones are abundant enough to give the name tuffaceous sand= stone to some of the material in the Orindin. The sandstones in the area are of several varieties,those in the intra- volcanic series consisting in the main of Graywacke sandstone, being of a prevailing gray color and carrying varying amounts of rounded or angular bits of shale,basalt,and chert. In the the southeastern portion of the area the sandstone is so extremely well indurated as to have at first glance the appearance of an igneous rock. (18) In the Orindan formation is encountered a buff yellow argillaceous sandstone,which apparantly is fairly well indurated by an iron cement. Its value as a water carrier may easily be passed up as it appears to be to firmly cemented to carry a great deal of water,however,upon placing this sandstone in a recptacle filled with water,it readily crumbles,and the grains easily separate. Even without making a size analysis of this sandstone it can readily be cou to be excellently sorted,and the pore space probabally amounts to around 30 percent. Structures: The northern limb of the Berkeley Hills syncline occurs in the southern portion of the area under discussion and dips into the hills at an angle of about 43 degrees to the south. This attitude,however,rapidly reverses itself within a distance of 1000 feet as one one follows the slope from Eureka Peak Ridge toward San Pablo Valley. The anticlinal structure thus formed represents but a minor fold in comparison with the great Berkeley Hills syncline,but its influence upon the topography is quite noticeable for this folding has weakened the c competent lava beds,and assisted weathering processes in the reduction of this lava covering so that in places the andesitic beds have been entirely removed,uncovering the sediments of the underlying Orindan. Such patches of the Orindan are well exposed on the slope just to the north of Eureka Peak,and in the cuts exposed along Tunnel Road. As the traverse is continued down the slope toward San Pablo Valley and up Lauterwasser Creek we pass through a series of folds. A synclinal trough in which are to be found several lava flows followed by an anticlinal arch and ending with a shallow syncline at the extreme northeastern edge of the map. (19) The general trend of these structures is about North 60 West and they are presistent in length throughout the entire area. The repétition of beds and the changes of dip make the location of the structural axis quite accurate in a cross section over favorable ground, but in tracing the axes over the alluvium covered hills their exact location is extremely difficult,in these places dotted lines represent the approximate location. Landsliding and minor faulting is quite prevalent in the intravocanic sediments. The formations dipping in the same direction as the slope of material the hills have aided the loose poorly indurated in its downhill creep,and in places this sliding has for a considerable distance covered the tver— lying lavas. The minor faults are of a displacement too small to map, but occur in many places in the shales and sandstones of the Orinden. The Pinole fault which is a prominent structural feature of the Berkeley Hills,also extends into this area in the extreme northwestern part but rapidly swings to the west and leaves the western limit of the map. The excellent structural map of the Berkeley Hillsby A.C.Lawson 1 gives a detailed describtion of this feature . Age of Formationsse Just off the southeastern limits of the map up Lauterwasser Creek occur the bituminous shales of the Monterey(Miocene). Imbedded in these shales were found well preserved whale bones. As this formation does not occur within the limits of the map,a description of the sediments will not be included in the report. The traverse was was extended into these sed- iments merely to determine the unconformable relation of the Orindan to the Monterey. The Orindan formation which includes the greater fortion of the area 1-See footnote on page (20) can with confidence be assigned to the Pliocene for it lies stratigraphically above the Pinole Tuff which is Pliocene. Mammalian remeins from this for- mation, examined by Prof.J.C.Merriam indicate Pliocene having affinities with the Miocene. Besides the fresh water ostracodes of the Orindan,fresh water mollusks have been recorded by 38 Bidper Pru the west side of San Pablo Creek along the road from Berkeley to Layfayette. These mollusks were also found imbedded in some lignitic shales up one of the smaller canyons just a short distance from the Tunnel Road. The Moraga formation,consisting chiefly of lava flows and subordinate sedimentary beds is found lying statigraphically above the Orindan and separated from it by the line of contact of the amygdaloidal andesite with fresh water deposits of the Orindan. The basis of the separation into two distinct formations seem,however,to be quite an arbitrary division and made chiefly to simplify the statement of geological relations. In the coarse of mapping the intravolcanic gravels,a portion of the Moraga, two horses teeth were uncovered. These specimens were shown to Dr.Stock of the Paleontology department and determined to be molars of Hipparion speciosum,of late Pliocene age. Geologic History:- The fresh water Orindan formation which is partly lacustrine and partly fluviatile accumulated in a synclinal trough- a trough which must have subsided as the formation was deposited in order to account for the great thickness of sediments. Volcanic ask’ occuring in the beds must have been ejected from distant volcanoes which were intermittently active. At the close of the Orindan time a depression must have on the . southwestern side of the structural trough in which the fresh water sediments Cooper J.G.On some Pliocene fresh water fossils of California. California Acad.Sci.Proc.2d Ser.Proc. Vol.4 p 169-1894. of the Moraga accumulated. Into this depression there wae poured a succession of andesitic and basaltic flows. Between these volcanic flows there were times when fluviatile and lacustrine conditions recurred and other times in which the lava was exposed to atmospheric oxidation and erosion. At the close of this time folding and faulting must have occurred which deformed the region into the present structural attitude of synclines and anticlines. The occurrence of the rether steep sided etreem trench which San Pablo Creek has cut in the alluvium clearly indicate that conditions have changed slightly in recent times. The former conditions of the region must have been favorable for vigorous downward corrasion of the streem,forming the canyon,leater the transporting power of the stresm wae reduced and it was forced to drop ite load making the valley broad and flat as we now see it. Since this time,however, there must have been climatic changes which increseed the volume of water supplied to the stream,or a slight uplift of the region ceusing San Pablc Creek to intrench itself in the earlier deposits of slluviumygiving the steep sided trench as it now exists. ECONOMIC POSSIBILITIES Limestone: ~ The limestone occuring in the area is of minor value. The limited amount available,its impure nature,and lens like occurrence give it little or no value for use in the making of cement,however,for road construction work it would make excellent sub-grade material. The owners of the property are now having several roads being built,in the construction of which,this limestone could be very profitably used. Lignite:- The small amounte of lignite observed in the area are negligible ae economic deposits. Vater:- The water possibilities of this region have in the past,proved to be a factor which has somewhat retarded the developement. The emall ephemeral streams which drain the area,during the summer months carry no water,while Sen Pablo Creek during theese months degenerates to insignificant size. Thus the water obtained must be from wells or springs. Due to a dieregard fot geologic structure the earlier wells drilled did not prove to be very satisfactory. An excellent example of one of the earlier failures ie shown in the water tunnel which was driven just to the north of Eureka Peak. At the contact of the intravolcanic sediments with the andesite a small seepage of water is to be observed. It was thought that by driving in a few feet from the contact a good supply of water could be obtained, the result,however,was just a slight increase over that which originally seeped out. Later another tunnel was drivea' sbout 100 feet below the firet. This supplied a considerable amount of water. The diagram below shows clealy that well No.2 should give the greater amount of water,due to the greater amount water bearing gravels drained. Senile 17: Foo Several other wells were drilled in eyncline occuring on the south side of Sen Pablo Creek,these were just mediocre wells and served to supply only a small amount of the necessary water. It was not until drilling was began in the Orindin formation on the north side of San Pablo Creek that a great deal of water was encountered. Here conditions were favorable,agood water bearing sandstome and excellent structure. The newest well being drilled in this formation occurs in the the syncline up Lauterwasser Creek,its location is indicated on the map. os i The possibilites for a good flow of water are extremely bright as the waler bearing sandstone is overlain by about 285 feet of impervious shale. Drilling through this shale and striking the sandstone the accumulation of water in the syncline should be great enough to supply most of the necessary water for Orinda. DISS £ LreyD ; GEol 1923 ene | Suen Z Tank Spring . ; | : | ih : Lime Stone ip, ore [autet 2%. Moraga Formation Andesite Tunnel well ? tr LJke Orit Andesite and Basalt flows Introvolcanic accumulations of gravels, sand stone, clayand Limestone. . . Orinda Formation Freshwater, con- qlomerate sand- stone clay lime MAPPED BY | oa LLOYD &L RSKINE |g loversof turf- Scale 1“=750 feet. Sea Leval Lime Stone A | ry S . a" ; | . ; [ : + : | Q, =] Xe. 2 2 figs | 5 Ni 5 ° v's 3 | i cy. ° oN 3 . EN ru] i Toe AOS = Loew LT cr wd J 13 Andesite Andesite and Basalt flows Introvolcanic accumulations of gravels, sand stone, clayand Limestone . . . a Oz 3 = B © Orinda Formation freshwater, con- qlomerate sand- MAPPE D BY - | Shane a’ lime LL OYD &E LE RSKINE ayersof Furf— Scale 1“=750 feet. el bi1 ell -~ ez Eure ka™ Peak Sea Leval END OF TITLE