california geology magazine september 1979

8/7/2019 California Geology Magazine September 1979

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GEOLOGY - Foundation of the present; key to California's Mure.

CALIFORNIA AND PLATE TECTONICS

~ , A L I F O R N I A(J-EOLOGY

35

September 1979

Callto.n'as p,esent geomo.ph,c p.ov,nces a re t he 'esult 01 gaotog,c p,ocesS(lS wh,cllhllva been lIct,ve to ! m,II'ons 01 years Some althese processes 1I,e S(ldtme''llal'on. volcanosm. plulon,c ,nl.uSlon. melamo,ph,sm. e.os,on. "" d tec!On,sm Fo ' it SI.'mmary 01lhe geOteClo",c developmanl 0' Calliorntll. see Ihe lIrttcle 0" pllge 187

Geologic Units

G.omo'ohl.o,,,.Tn bo"""""G.olo9lc unll boundo,)foull~ j ' ~ ' t ~ ~ " ~ ~ ~ ~ ~ I O O MILES"0 80 t60 KtLOMETERS

SCALE

Generalized

GEOMORPHIC PROVINCESOF

CALIFORNIA

D Quot"no" ..dlmont.,) ,ock. To, 110" .od""ont." , k,

Ouot.,no" and T... tlo' , .ot .on"'o .k, 01 CASCADE RANGE ondMODQC PLATEAU

, "

,

-

! ' lJr 'to1 " 0 ~ " , , 1 Iw,/I,."


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Note: This article summarizes the contents of the first Rubey Volume. a new series in Earth andplenetary sciences. nemedinmemoryof the lateW.W. Rubey. Profe.lOr of Geology end Geophysics at the Uni-

versity of C.tlifomie Los Angeles IUCLA)and career scientist for the U.S. GeologicalSurvey. ElIch volume will present the written product of an annual UCLAcolloquiumon a tepic of interest to geologists and

space scientists. Rubey Volume No.1 entitled THE GEOTECTONIC DEVELOPMENTOF CALIFORNIA describes the plate tectonic framework of the state and adjacentregions.AN INTERPRETIVE ACCOUNT

D D D oD

ByW.G. ERNST. Chairman

Department of Earth and Space SciencesUniversity of Californie. Los Angeles

D

o

Figure 1 Diagrammatic sketch of the four major types of continental margins showingcruslal topologies: (a) Atlantic type. divergent margin: (b) Andean type and (c l Japanese type. Both (b) and (c) are convergent margins (nOI shown is oblique subductionor possible tectonic removal ollhe leading edge of the nonsubducted slab): (d) Californian type. transform margin.Lithosphere-asthenosphere contact not illustrated.AfterDic-kinson. 1976.

"

complex interplay among diverse constructional and destructional processes.The Atlantic type (figure la ) is a riftedmargin produced by divergent plate motion. Both the Andean type (figure tb)and the Japanese type (figure tc ) areconvergent plate junctions. TheCalifornillDtype (figure Id ) is characterized by strike~ l i p movement, and it is, therefore, aconservative plate boundary. The convergent models (Andean and Japanese) may

(bl ANDEAN TYPE -..-subduclial bean: P'Jklniccomplex basil arc= = = = ~ -;;;;,.(dl CALlFOONIAN TYPE

rifled bc:rde!tlnd

CONTINENTAL MARGINSAND THE GEOLOGYOF CALiFORNIA

(01 ATLANTIC TYPE rOOr}eocIile 011100~ ' T ' ( " " "

There ace four principal types of lithospheric plate boundaries involving continental margins. They are: (I ) theAtlantic, (2) the Andean, (3) the Japanese, and (4) the Californian (figure I) .The geology of each margin is a functionof its own unique history and represents a

The present-day geology of Californiais an intricate lithotectonic collage. Lithotectonic belts reflect the complex inter play between semicontinuous igneous,sedimentary, and tectonic constructionalprocesses and the episodic occurrence ofdestructive pla te motions which havetruncated, pulled apart , d ispencd, andcarried away segments of the continentalcrust.

INTRODUCTION

The geologic history of California isunique and complelt. Dynamic interactionsof lithospheric plates through time haveleft intriguing puzzles yet to be fully solved.The following article summarizes the findings of many workers studying plate tectonic geology in California. Because of thenature of the subject. the geologic concepts m ay be unfamiliar to many readers.To help the reader understand this description of Ihe processes which led 10 thepresent geologic configurl ltion of thestate. a glossary of plate tectonic terms isincluded wilh this article (p.194). A briefsummary of the basic concepts of plateteclonics can be found in the Oct. 1978 is-sue of CAliFORNIA GEOLOGY ....Editor.

California Geology september 1979 187


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Figure 2 Aspects of the generalized regional geology of California. InpartllfterH8milton.'978. Major faults: Coast Range thrust (CAT); Garlock (G); San Andreas (SA); SanGabriel (SG); San Jacinto (SJ); San Simeon-Hosgri (SSH); Other abbreviations: GrestValley sequence (GV); Pelona and Orocopia schists (Pl.

Portions of the San Gabriel Com:p\a.have been fragmented and reasaembled atdifferent times, and some portions areprobably still being modified due to ongoing t ransla tional mot ion along the SanAndreas fault system. Lithologies preserved in the SanGabriel Mountains indicate continental metamorphism at deepcrustal levels, and the addition of bothmafic and felsic calc-&1kaline igneousmaterial. The oldest rocks are theMendenhall Gneiss and related quartzo....feldspathic gneiss-amphibolite complexof 1715 30 m.y. age, intruded by 1670 15 m.y. old granitic gneisses. The SanGabriel anorthosi te - gabbro - syenitecomplex was emplaced about 1220 10m.y. before present (b.p.). The thermalaureole produced by this differentiatedmafic pluton caused the amphibolitization of rel ict granuli tes in MendenhallGneiss on the south and southeast margins of the anorthositic complex (pbotoI). I t is not known i f an early stage ofmetamorphism attending intrusion produced the granulites (Ehlig, in press), orwhether tbey formed prior to emplacement of the anorthositic complex, atabout 1440 m.y. ago (Silver and otben,1963).Mojave Desert Province

Two major belts of ancient crystallinerocks have been recognized based on ge0chronologic data for cogenetic z irconsuites in granites and their country rocks(Silver and Anderson, 1974). The olderterrane t o the northwest is characterizedby a 1820m.y. oldmetamorphic basementintruded by granitic plutons which are100 m.y. younger. The younger, moresoutheasterly terrane consists of 1720m.y. old country rocks intruded by 1650m.y. old granites.

It has been bypothesized that ancientcrystalline belts were juxtaposed in earlyMesozoic time by a left-lateral stri.ke-slipfault which transccted theMojave Desertin a roughly north-south direction. As inthe San Gabriel Mountains, this Precam-

Transverse Ranges Province

Isolated masses of Precambrian basement rocks protrude through a veritablesea of alluvium in the MojaveDesert. The basement rocks are intrudedby Mesozoic granitic rockand overtain by volcanogenic units.Limited lateral continuity hampers regional correlations, but where outcropsoccur , they are almos t completely ex-, .". . .

,,,.

Occurrences of Precambrian rocks inCalifornia have been hypothesized in several batholi th ic terranes, such as theSalinian block. of the Coast Ranges, a l though Precambrian rocks are knownwith certainty only from the TransverseRanges (San Gabriel and San BernardinoMountains), the Mojave Desert,and the Basin and Range provinces.

tory is somewhat obscure. NC'\etheless,we know that lithosphere, hydrosphere. and atmosphere bad evolved to es.-sential ly a modern aspect by about 2,000million years (m.y.) ago (Windley,1977). Crustal sections from that time 00-ward can be correlated in large part withcurrently active earth-building processes.A notable exception is the apparent lackof ophiolites; sensu stricto,which wouldrepresc:ot an early phase of sea floorspreading prior to Phanerozoic time.

Basin and Range'-'-MOdoc:Plateau !II:.::'., i

",Iit"

,..

\ ' \ '...,'"\ ...,,,o Late \Mesozoic'-?(Franciscan ::'terrane \co oS'

\? 'S'..yo Late Meso- \"';'. .. ~ < ; G VZOIC granitic \-0,-

terrane \ c " " l ~ " : ' i : : 4 ~, 0""" M'd Me . '!s \ ' - \dlliJ r SOZOIC Un! \?o '\[J3 L a r g e ~ Poleozaic units \ \ ' \ - . . ~\ GV \Ophiolitic complexes \ \

" " \" " \120. " " : : - , ~ , ~ r d e ~ l o n d

The present-day disposition oflithotcctonic belts in California is sbown on figure2 (Hamilton, 1978).

The preserved Precambrian lithologicsections in Californiaare limited and fragmentary. Consequently, the deduced his-

PRECAMBRIANHISTORYOF CALIFORNIA

involve pure "head 00" subduction, butoblique underflow is apparently morecommon. In either case, the convergentmotion may result in accretion of reworked sialic (silica-alumina-rich) material adjacent and landwardof the trench,ortectonic erosion"of segments of the c o n t i ~oental margin (oot shown on figure 1)may occur.

18. California Geology september 1979


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Figure" Hypothetical. generalized diagram depicting the Antier plate tectonic regime.not to scale. In this interpretation. westward subduction is postulated to be responsiblefor the eastward overthrusting of the Antler allochthon. After Poole and Sandberg. '971.

DEVONIAN-MISSiSSIPPIAN

croton

In the Klamath Mountains province, ageneral trend of units becoming youngerto thewest and the tectonic imbricationofmiddle and upper Paleozoic and Meso-zoic units along eastward-dipping thrusts(Irwin, 1960; 1917) suggests that subsequent to the Antler orogeny, the paleopacffic plate descended t o the east beneaththe accreting continental margin. Herethe east-dipping Trinity thrust juxtaposed the eastern Paleozoicand Triassiceugeoclinal section - a marginal basinassemblage (7) which appears to correlatein part with the northern Sierra NevadaShoo Ay Formation - and the underlying Trinity Ophiolite against the structurally lower, more westerly centralmetamorphic belt. The age of metamorphism of this belt, 380-400m.y., suggestsa Devonian event. However, the time of(mal assembly in the eastern KlamathMountains, judging by late Paleozoicearliest Mesozoic depositional ages. indicates that late slages of the thrustingprobably should be correlated with aphase of the Sonoma orogeny (latest Permian to earliest Triassic time). The platetectonic interpretation of the central

construction of a late Paleozoic volcanicarc lyingwestofa newly formedmarginalbasin. The latter was presumably the siteof accumulation of the Calaveras Formation. Unlike the present-day Japanese archipelago (a typical island arc) whichfaces the subducting oceanic crust-capped lithospheric plate, these Paleozoicisland ares of central California apparently faced North America, reflecting westward underflow of the marginal basin.This volcanogenic unit const itutedthe leading edge of the continental crust-capped slab. During the Sonoma orogenyat the end of Permian to earliest Triassictime, this lithologic plate moved eastwardalong the Golconda thrust towards theNorth American craton (figure 5).Klamath Mountains Province

Antler forelondallochthon clastic

be"marQinelbasin

Klamath-N. SierranIs land a reerc-trench QCIP

Renewed subduction offshore at thelatitude of the Sierra Nevada allowed the

Sierra Nevada Province

(Salinian block) in the west-eentral portion of the state. in the Mojave Iksertprovince, and in the TtarulveneRanges province (San Gabriel Mountains) to the south. Judging from unitthickness and sedimentary facies trends,the ancient Pacific continental margin ofNorth America trended roughly north-south, from southernmost Idaho and central Nevada into southeastern California(figure 3) prior to the Ander orogeny ofLate Devonianland Early Mississippiantime (Burchfiel and Davis, 1972; Stewartand Suczck, 1971). The onlapping sedi-ments have a thickness of about I kID onthe southeast near the shelf edge, andthicken northwestward to a section ofnearly 10 km. One or more early Paleozoic island ares were located t o the westin the provinces of the Klamath Mountains and northwestern Sierra Nevada(68'=4).

In latest Devonian-earliestMississippian time an eastward-directed overthrusting along the Roberts Mountains. thrustbrought volcanogenic argillites of a subduction complex over an autochthonousmiogeoclinal sequence (Stewart andPoole, 1974). The Antler orogeny signaled the closure of an intervening marginal basin (figure 4) and the suturing ofisland arc material onlo the western pe-rimeter of North America. The Shoo AyFormation in the northern Si-erra Nevada bears; evidence to this event.Dickinson (1971) presented the case forwestward consumption of the marginalbasin, whereas Burchfiel and Davis(1975) explained the suturing eventthrough a process of eastward platedescent involving uncoupling and overthrus ting (obduction) of the island arcsuperstructure.

PALEOZOIC HISTORYOF CALIFORNIA

Figure 3 Generalized plate tectonic setting of California during the Antler orogeny(Devonian - Mississippian Period). Aftervarious sources. including Burchfief andDavis. 1972: 1915: Dickinson. in press.,

DEVONIAN-MISSISSIPPIAN

Precambrian rocks are found as farnorth as DeathValley, where they are unconformably overlain by a weakly recrystallized sedimentary series of latestPrecambrian age. These strata, and theoverlying most recent Precambrian and lower Paleozoic section,represent well-sorted, chemically maturesediments produced along an Atlantic-type continental margin (Stewart, 1972).The initiation of rifting resulted locally information of the Amargosa aulacogen(fault-bounded intracratonic trough orgraben). Thus the time m1er'Yai fromlatest Precambrian to earlyPaleozoic was dominated by shallowwater, passive margin-type deposition(such as formed the Pahrump Group) inthis portion of California.

Rocks of Paleozoic age are present inlarge tracts of eastern Califomia (SierraNevada province) and crop out as farwest as the Klamath Mountains provincein the north western area of the state,possibly in the Coast Ranges province

Basin and Range Province

brian terrane reflects deep-level sialic ad-ditions to the continental crust. Simila.rmetamorphosed rocks crop out to thesouth in the San Bernardino, Chocolate,and Orocopia Mountains.

California Geology September 1979'"


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So=>allochthon

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Much of the Franciscan Complex hasbeen thoroughly tectonized in contrast tothe rather orderly Great Valley sequence.The two terranes arejuxtaposedalong thegenerally ea st -di pping Coast Rangethrust and related faults (Bailey and others , 1970) (photo 3). Movement alongthis system may have OCCllITed at varioustimes in the Cretaceous and early TertiaryPeriods subsequent to initiation of thesubduction zone about ISOm.y. ago. Priorto the westward movement of this junction, the convergent lithospheric plateboundary lay roughly 100 kIn to the eastin the vicinity of the Sierran westernFoothills bell. The time of s tep-ou tmust have followed generation of theGreat Valley ophiolite at 155 5 m.y.ago (Lanphere, 1971; Hopson and others,t975), but before deposition of the overlying Tithonian cherts 140 m.y. ago ( P e s ~sagno, 1973). Alternatively, Schweikertand Cowan (1975) have suggested thatthe ophioli te represents oceanic crustf looring a marginal basin which lay immediately to the west of an east-facingwestern Sierran island arc. Althoughlarge components of northward movement of the oceanic lithosphere have beenpostulated (Jones and others, 1978), thecontrasts in deformation and in inferredpressures of metamorphic recrystallization across the Coast Range thrust system

CRETACEOUS-EARLY TERTIARYFrmciscon subdue/ion .. ,"c.

.. """"".' ~ . : ~ < ~ : ' : ; ~ ~ L - '/1'_.";" _'- P,. ....\... .. va. ., ... .. ,"' ...... '\ . . . . I..\ \ . ' . i . . ..\ \ \ ~ ( .......... ftl........ l ; ~ { ] \ , . . . . . . . ~ ' I C - , u l \ ' ' ' ' 1 C " \ \....., ore ' ii \ - . . . . . . . . . . " . :fi!\ ~ ' . ' . ' . ' . rI: .:.;:',; (,;NG"'" 11>, '.,. .. . . . . . .. - / ... ";.... -:::::.->

Figure 7 Plate tectonic setting of California during tha Cordilleran orogeny (Cretaceous-Ear lyTertiary Period). After vBrioussources, including Dickinson. in press.

tary mBaDges, representingmid-submarine fan and olistostromalunits, respectively, were deposited exclusively on an allochthonous oceanic s u strate---the capping crust of one or morepaleopacific plates (figure 7).

The Great Valley-Franciscan coupletlies on the Pacific Ocean side of the Klamath-Sierran volcanic-plutonic belt. Although its plate tectonic setting has beenrecently reinterpreted as a striko-slip collage (Jones and others, 1978), this pair ofl ithologic belts has been widely recognized as a classically developed arct rench gap section and trench milange,respectively (Dickinson, 1970; Page,1978). Both assemblages consist chieflyofpoorly sor ted, f lrs t-cycle clast ic sediments derived in large part from the adjacent calc-alkaline volcanic-plutonic arc(Dickinson and Rich, 1972; Jacobson,1978). At least the Cretaceous portion ofthe Great Valley sequence represents amiogeoclinal wedge laid down on thewesternmost Sierra Nevada, Klamath Mountains, Salinian block, and Peninsu la rRange basement and immediately seaward oceanic crust-all generally regarded as portions of the North Americanlithospheric plate. In contrast, the Franciscan coherent turbidites and sedimen-

Although some older ophiolitic units ,such as the Kings-Kaweah complex,seem to have boen tectonically transported thousands of kilometers northward during early Mesozoic sea floorspreading, the northwest-trending tec-tonostratigraphic and batholithic belts inthe Sierra Nevada seem to reflect stagesinvolving large components of oblique lithospheric plate convergence (figure 6).The Sierra Nevada foothills suture constitutes the contact between Mesozoic accretionary terrane and the more easterlyPaleozoic basement terrane.The KlamathMountains and theSierraNevada are correlatable in terms of their petrotectonichistories (Davis, 1969); but the SierraNevada terrane probably represents exposure of somewhat deeper structural levelsthan the Klamath Mountains. Westwardmovement of the Klamath Mountainscomplex relative to theSierra Nevada beltappears to have begun by the end of EarlyCretaceous time (Jones and Irwin, 1971).Total left-lateral strike slip displacementon this series of tear faults was approximately 100 km.Coast Ranges Province

Mariposa--Smartville complex, equivalentto Rogue--Galice-Josephine units of theKlamath Mountains, is predominantlyearly to mid-Mesozoic in age. The complex lies oceanward from the more eas terly, predominantly Paleozoic sectiOn. Ingeneral, stratigraphic tops of the uni tsface eastward in both younger and olderwestern Sierra Nevada terTanes (Bateffienand Eaton, 1967). '

Figure 6 Plate tectonic setting of California during the Nevadan orogeny (LateTriassic-late Jurassic Period). After VBr-ious sources. including Dickinson in press.

(Bateman and Eaton, 1967; Bateman,1974). AJthoU8h the earliest bodies are asold as Triassic, the major batholithic units are Cretaceous in age (photo2). Five major intrusive episodes in theLate Triassic-Late Cretaceous time spanare recognized (Kistler and others,1971). These epochs, each of which in-volved intrusive events over a 10-15 m.y.interval, are separated in time by about 30m.y. The initialmSrr'Sr ratios of the gra-nitic rocks appear to reflect the relativeproximity to the Mesozoic continentalmargin (Kist le r and Peterman, 1973).Evidently the magmas interacted isotopically with the pre-existing crust duringassimilAtion or anatexis, or the melts werederived from isotopically distinct portionsof the upper mantle. Al l of the batholithicrocks possess textures indicating emplacement as crystal mushes - hence it is difficult to see how the magmas couldrepresent uncontaminated, high-temperature l iquids derived direct ly from themantle.Remnants of the volcanic country rockinto which the plutons were intruded,such as the rhyodacit ic Ritter sequence,are confined to central and eastern SierraNevada roofpendants. Eastward-dippingreverse fault s in the Weste rn Foothi ll sbelt havejuxtaposed oceanic crust againstthe continental margin (Saleeby, 1978;1979; Saleeby and others, 1978).This tectonic regime, the Logtown Ridge-Mariposa-Smartville complex, containssubduction zone olistostromes, ophiolites,

calc-alkaline volcanic island-arc rocks(andesites and dacites), and eugeoclinalsedimentary rocks. The Logtnwn Ridge-

cali /omia Geology september 1979 19'


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require periods of rapid convcrgmoc andprofound underlIow of theFranciscan terl'UIe prior to decoupling from the subducting slab (Ernst, 1965, 1911; Suppe,1972).Peninsular Ranges/Related AreasMost of theMesozoic volcanic and granitic rocks of the Mojave Desert (including the San Bernardino Mountains), thegraniticsliver that constitutes theSalinianblock, and the Peninsular Ranges batholith represent southward prblongations

of the Klamath-Sierra NC'lada volcanicplutonic arc. These units mark the mid tolate Mesozoic continental margin ofNorth America, although Cenozoic translations along the SanAndreas tnnsformsystem have displaced segments of thistemme 300 k.m to as much as 550 k.mnorthwest of their original positions(Page, in press).Plutons in the Peninsular Ranges aregenerally similar to plutons in the SierraNevada. The more mafic plutons in thePeninsular Ranges possess low initiallIISr;e'Sr ratios and exhibit unfractionatedrare earth element patterns. These maficplutons occur on the west side of the Peninsular Ranges. The more silicic, morepotassic, plutons with higher lIISr;e'Srratios are situated progressively farthereast. In addition, the age of post-Jurassicgranitic emplacement and crystallizationtends to decrease towards the craton. Plu

tons on the south and west are characteriz.ed by very highKlRb ratios, analogousto isotopically primitive island arcs; thisratio decreases in granites of the northernand eastern Peninsular Ranges: Gast iland others (1978) have proposed that thewestern, more mafic portion of this terranewas an island arc constructed on oceanic basement, whereas the more easterlyvolcanie-plutonic belt was sited near theNorth American continental margin.Eastward consumption along two parallelsubduction zones is presumed to haveobliterated the hypothesized interveningmarginal basin, with collision and fmalsuturing occurring in earliest to mid--Crctac.eous time.Southern Extent of Great Val ley Franciscan CoupletThe California borderland, includingthe islands of Santa Catalina, Cedros, andSan Benitos, as well as Palos Verdespeninsula and San Sebastian Vizcainopeninsula, contains the southern equivalents of theGreat Valley-Franciscan couplet. The presence of this terrane,although poorly exposed and complexly

" l T S,'ve'. p.'.""o' cOmmunoc.lIon. 1978

faulted IUpporta the theory d alate Mesor.oic convergent boundarymarking the western termination of theNorth American lith08pberic plate. Thegreat width of this terrane suggests tectonic duplication accompanying strikeslip faulting (Howdl and Vedder. inpreu).Transverse Ranges ProvinceThe Transverse Ranges in general, and

the San Gabriel Mountains in particular,contain some of the most puzzling Mesozoic rocks exposed in the state. The a1kaIi c 220 :!: 10 m.y. old Lowe Granodioritehas intruded the Precambrian and Paloe>zoic(?)scctions. Plutons of early Triassicage, which are similar to plutons in theSan Gabriel Mountains, have been emplaced in the Mojave Desert. San Bernardino Mountains, and the Wbite-InyoRange (Miller, 1977; 1978). The occurrence of these plutons possibly indicatesthe onset of Mesozoic lithospheric plateconvergence and inferred deep-seatedpartial fusion of subducted, eclogitizedoceanic crust . This Mesozoic volcanicplutonic terrane passed eastward to a"shallow" back--arc sedimentary basin inthe easternMojave Desert (Burcbfiel andDavis, 1975). The San Gabriel Mountainsare also the site ofseveral Cretaceous granitic int rusions, which have induced ametamorphic overprinting on the adjacent country rocks.

About 55-60 m.y. ago, this calc-al.k.aline plutonic arc complex apparently wastectonically transported en massnortheastward over the eugeoclinaJ Pelona Schist terrane along the gently westdipping Vincent thrust (Ehlig, in press;Graham and England, 1976). The PelonaSchist (Orocopia) protoli th was deposited in a late Mesozoic back-arc basinwhich may have been a southwesterly,more oceanic extension of the shallowdepositional basin of the eastern Mojavecontinental regime. After deposition, therocks were deformed and recrystallizedduring southwestward subduction accompanying latest Cretaceous closure and destruction of the depositional trough(Haxel and Dillon, 1978). Evidence implying the above modd includes areal andstructural disposition of the PelonaSchist, and both relict volcanoclastic andnew, relatively high-pressure metamorphic mineral assemblages. Fragmentsof this hypothesized marginal basin sequence arc dispersed along the San An-dreas fault, extending from the C8SternTransverse Ranges southeast to the Sal-ton Sea and into southwesternmost Ari-rona.

The PcIona Schist bu alternativelybeen interpreted as a Franciscan equivalent that was initially deposited to thewest, and laterwu subducted to relatively&hallow depths far to the east beneath thecale--alkaline plutonic arc (Yeats, 1968;Burchfiel and Davis. in press). The rockssub3equc:ntly were displaced upwards toreappear in windows framed by the overlying granitic terrane.Whatever the origin and sense ofmovcment on the Vincent--COCOpia thrust sys

tem, the rocks of both upper and lowerplates seem to have reached their metamorphic culminations in the present locat ion relative to one another-hencerecrystal liza tion evidently outlastedthrusting. In contrast, the Coast Rangethrust (with which this system is oftencompared) juxtaposed rocks of differentmetamorphic ages and pressure-temperature conditions of formation-that is,thrusting outlasted metamorphism.

CENOZOIC HISTORY OFCALIFORNIAVolcanismVolcanic rocks, predominantly of calcalkaline affinities, were erupted in much

of the eastern portion ofCaliforniaduringCenozoic time. Cenozoic age volcanicrocks are also located sporadically in theCalifornia Coast Ranges and westernTransverse Ranges. The Modoc Plateauconsists of extnasive units (photo 4)representing the southern terminus of thecurrently active Cascade MountainRange and its Tertiary volcanic arc andplateau basaltic precursors. Continentaltholeiites, high-aluminum basalts, andesites and dacites are widespread in thisnortheastern portion of California. Thesevolcanic rocks presumably represent thesuperjacent covering of continental margin cale--alkaline plutonic rocks and back-arc lavas generated over the eastwarddescending Farallon lithospheric plate.

Farther to the southeast , in the blockfaulted, extensional Basin and Range andMojave Desert regions, alkalicbasalts occur in the volcanic assemblage,indicating the derivation of magmas fromdifferent upper mantle (as well as crustal?) levels. This change in basaltic composit ion may reflect the transit ion fromearly Tertiary pla te convergence to theongoing state of complex northwesttrending right-lateral transform motionin Miocene time. This transform motionalso involved east-west crustal extensionas well as local compression.

California Geology September 1979


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-Photo 1. P r e ~ m b r i a n anorthosit..-gabbro complex in the SanGabriel Mountains.The differentiated mafic pluton exposed in thisroadcut was formed by the settling of crystals from the magmo.resulting in II cumulus. llIIysred structure. The top o f the magmachamber is on the right indicating post-crystaUiUltion til ting ofabout 90'. The light-colored diapiric structure in the left center ofthe photo. which is composed almost exclusively of enorthosit9.clearly indicates the top of the magma chamber during crystlliliullion. Photo by W.A. Srpnt.

Photo 2. Mesozoic granitic rocks form the steep eastern lace ofthe Sierra Nevada; view from lone Pine. in Owens Valley. lookingwest. The Alabama Hills, composed of Mesozoic volcanic andgranitic plutonic rocks. occupythe foreground. The earthquake of1872 occurred along the Owens Vallev fault. a segment of whichpasses ecross the foreground just beyond the fence. Photo byWA. Bf)'lInt.

Photo 3. Deformed segment of the Soda Creek thrust. a seg-:-"ment of the Coast Range thrust (1). in the Coast Ranges. south ofClear lake: view east. Sheared mudstone of the OpperJurassicKnoxville Formetion is to the left of the fault zone: serpentinite liesto the right of the fault. The Knoxville Formation is the basal mem.ber of the miogeoclinal Great Vallev seQuance. The isolated serpentinite at this location may belong to the eugeoclinal FranciscanComplex. but post Mesoloic deformation has obscured the evidence. Phoro by WA. Bry4nl.

-Photo 4. Surprise Vallev fault l ine scarp. lookingsouth-southwest from Surprise Valley. CenOloicWerner basalts comprise the tilted fault block of theWarner Range(background). The structural geologylin this portion of northeasternmost California is characteristic of the Basin and Range geomorphic province. but the lithology is more representative of theModoc Plateau geomorphic province. Photo byWA.8ry4nt.

cali fornia Geology September 1979 193


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l'binping of the crust and uaociatedvolcaniam. aloog a northern extrapolationor the Eut Pacific Rise (Menard, 1964)may rdlect baek--&rC spreading in the B a rio and Range province (Stewart. 1978).The top of the low-velocity zone in themantle (asthenoephere) is at the base ofthie attenuated crust, and along with highbeat now measurements, indicates thepn:IeDt-day cxiste:nce of a diffuse mantleheat source beneath the Basin and Ranacprovince. Ovcrridinl of the Eas t PacificRise can be inferred from eumination offigme 2.

The Coast Ranges and western portionof theTransverse Ranges bear evidence ofwidespread basaltic and calc-alkaline volcanism and hypabyssal intrusion fromlate Oligocene time to the present. Theserocks are of secondary importance.however. compared to the voluminousclastic 5Cdimcntary units. Igneous activityappears to be related to a thcnnal eventassociated with the proJI'CSSively pa.terover-riding of the Rut Pacific Rise t h c r ~mal anomaly commencinl approximately29 m.y. ago (Atwater, 1970; Hawkins,1970). The shallow level of derivation ofthe melts is indicated by the absence ofalkali bualts and hypcral.kalic felsic plugs.Depositional BasinsCenozoic marine depositional basinscovCl'Cd most of the western half of thettate bu t are curTeI1tly mueb reduced inareal extent to the present-day narrow

continental shelves and the moderatelybroad southern California borderland. Incontrast, continental deposition has pmcecdc:d at high local rates in the Basin andIlangc province, and in.parts of the GreatValley, theCoast Rangcs, the MojaveDeeer t and the Tranlvcrse Ranges provinces.Tectonic DevelopmentBoth on-thore and off-6horc areas arecharacteriz.ed by hent and graben strue

tuns; the California Coast RanICS andborderland are also typified by moderately intense folding. rdlcctinl loc:al compression. Increasing numbers of rotationsand pu.U--.part structures associated withthe San Andreu strike-sl ip system inwestlm California arc being rccogniud(Crowell, 1974; Hall, 1978). Positivetopographic areas along thiJ shear systemreflect "locking bends" where excess masshas accumulated; the San Gabriel Mountaim represent a prime cu.mple. Becausethe transform boundary transects the c o n ~tinental margin at a low angle. n o r t h w e s t ~ward tranlpo rta ti on of the Saliniaa-Nacimicnto block relative, to the

North American plate . . . . duplicated thevolcurio-plutoaic an; aro-tn::neb pp,an d aubductioo. zone in the ocntral CoastRanges and borderlaDd (Crouch, 1979).Although the pracnt-day kinematicdeformation is complex, movement along

the San Andreas fauJt system in generalappcan to have stepped eastward withtime. Earlier stages of Ilip on the San Andreas fault system occumd chiefly alongthe San Simeon-HOllgri, southern California borderland complex. and San Gabrielfaults during slivering of the Salin.ianblock (Hall, 1975; Crowell, 1975; Howelland Vedder. 1978). Movement along thefault system has gradually int.cnsified onlater breaks sueb as the San Jacinto andHayward faults (AlIco, 19S7; Garfunkc1,1974) (figure 2). This eastward migra.tion of the active strike-elip zone probably is a resultof the progrcssiveovcrr:idingof the East Pacific Rise by the NorthAmerican continental crust--capped lithospheric plate.Measurements of the ~ c o t mag-netismofMiooene volcanic rocks from thewestern TransvcncRanges indicate Cl'Up-tions at about 10" lowermagnetic latitude.

An approximate 7S clockwise rotation ofthese uni ts occur red durinl tectonictransportation to their present location(Kamerling and Luyendyk, 1m ; 1979),Such rotation implies that individual scgments of the weatlm Transverse Rangesmay have behaved as coherent blockscaught in themaster right-latera1San An-dreas fault syst.cm.Eaatcrnmost California duringCenozoic time was the lite of subdue.

tion zone ca1c-&lbline igneousactivity-Ioc:ally cxtinJUished by the cessation of convergent lithospheric platemotion-block faultinl and extension,uplift (espccial ly in the batholi thic terranes), and local continental aUuviation.Western California was subjected to wid&spread but retreat ing marine embaymenta, rest ric ted igneous activity ofexclusively shallow derivation, loc:al compression and oblique rifting-all associated with an early stage of obliquesubduction, gradually s.ucceeded by theNorth American-Pacific transform. system. This major strain system, althoughsimply expressed within the ocean basin,has taken on a very complex aspect in themedium of sialic crust.Sea Level FluctuationsA final point of interest involvcs fluctuations in sea level. While studyinl thebathymetry of mid-occanic rift systems,

PatIClIlJ and Sclater (1977) recopiu:dthat water depths are rouJbly proportional to the age of the oceanic lithosphere;hence as themean age of the ocean buin5increases, sea water tends to drain fromthe contincots. Diclrinson (in press) haspointed out that world-wide marineregressions should be characteristic oftimes in which yOUDI oceanic crustcapped lithosphere is preferentially subducted-as wouJd be the case when NorthAmerica encroached upon the Rut Pacific Risc. Thus the local obliteration ofthis ridge system alonl the Californiacoast in mid--Cenozoic t ime could havebeen responsible for the ubiquitous hiatusin shallow marinedeposition on the continents and the flood of t.crTcstriaillCdimentation durinl OliJOCClle time. It alsoseems likely that regional elevation of thelithOlphere would accompany the overriding of the ridge crest by the leadingedge of the continent.

GLOSSARY' " parI. after GloSS8ry of Geologr.American Geological Instml la. /972.

allochthon - a mass of rocks that has baenmoved Irom its original site 01 origin bytectonic fOfces. as in a thrust sheet ,

anatexis - melting of preexisting fockaulacogen - a fault-bounded i"tracratonic

lrough or graben.autochthon - a body of rocks tha t remains

al it s sile of origin, where il is rOOled 10its basemenl I rocks may be mildly toconsiderably deformed) .

cralon - a part o f the Ear lh 's c ru st whichhas atta ined stability. with litlle deformation over a long per iod of time.

eugeoellne - a re a o f con tl nenu l r is ewhere strata areldeposi ted on th eocean floor beyond thelcontlnentllslope; vo I canogen 1c I sed; ments\arederived from th e landward arc.

hypabyssal - pertaining to an igneous intrusion. or to the rock of that intrusion.whose depth is intermediate betweent hat of abyssal (great depth) and thesurface.

i sl and arc - curved chain of iSlands. generally convex to war d t he open ocean,margined by a deep submarine !fInchand enclosing e deep sea basin.

lithosphere - Upper, relatively brittle layero f th e Earth.

l i thotectonic - a term used to descrlbe l an assemblage of rocksformed in a par t icular tectonicenvironment.

". California Geology September 1979


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megashear - a s tr ike-sl ip lault 01 such eKtent that it underlies the entire orogenicbelt.

miogeocline -area of continental rise strata deposited on the ocean Iloor beyondthe continental slope: volcanism is notassociated with sedimentation.

Olistrostrome - a sedimentary deposit consisting 01 a chaotic mass 01 intimatelymiKed heterogeneousmaterials that accumulate asa semilluid body by submarine gravity sliding or slumping ofunconsolidated sediments. It is a mappable. lens-like stratigraphic unit lackingtrue bedding but interca la ted amongnormally bedded sequences .

ophiol i te - II group of mafic and ul-tramafic igneous rocks rangingfrom sp l l i teand basalt to gabbroand per idot i te , IncludIng rocksrich in serpentine, chlori te , epidote, lind albi te derived from themby la ter metamorphism,whoseorigi n is associ ,Hed wi th th e formation of a sprellding center.

petrotectonic - structu,al petrology. includ""g or eKtending to analysis 01 themovements that produced t he r ock' slabric.

P h a n ~ " o z o l c - t ha t p ar t 01 geologic limelor which. in the corresponding rocks.the evidence ollile is abundant (especially higher lormsl .plotolilh - unmetamolphosed r ock from

which a given metamolphic rock wasformed by metamorphism.

stnke-sllp - in a lault the component of themovemenl or slip that is parallel to lhestrike of the fault I horizontal displacement)

"Sr/"S, - stronlium isotopic ratios used todetermine the nature of the parent rockfrom whIch magnas are derived and theamounl 01 contamination. The Sr laliois usually low for most oceanIc igneousrocks and hIgher for continental rocks

lectonlC erOSIon - removal by subduction01 malerial from the under side of anoverridIng lithospheric plate.thermal aureole - a zone surrounding an

igneous Int,uSlon in which the countryrock shows the effects 01 contactmetamorphism.

REFERENCESAllen. C.R., 1957, San A n d r ~ s faulL zone inSan Gorgonio Pass. southcrn California:GtQlogical Society or America Bulletin. v.68, p. 315-350.A l v a r e ~ W.. Kent. D.V .. P,cmoli Silva, I.,Schweikert, R.A.. and Larson, R.L., 1979,Franciscan limCSlonc deposited at 17southpaleolatitudc: Geological Socicty or America. Abstracts with Programs, v. 11. p. 66.

Atwater, T., 1970,lmpUe.tionsofplate tectonics for the Cenowic tectonic evolution ofwestern North America: Gcolosical Sodetyof Amerie. Bulletin., 'I . 81, p. 3513-3536.Bailey, .H., Blab, M.C., and Jones, D.L,1970, On-land Mesozoic oceanic crust inCalifomia Coast Ranges: U.S. GtQlogicalSurvey P r o f ~ i o n a l Paper 700-C, p. C70C81.Bateman, P.C., 1974, Model for the origin ofSierra granites: California Geology, 'I . 27,no. I, p. 3-5 .Batematl , P .C., and Dodge. F.C.W., 1970,Variations of major chemical c:onstituenuacross the central Sierra Nevada batholith:Geological Society of America Bulletin, v.81, no. 2, p. 409-420.Bateman, P.c., and Eaton, J.P., 1967, SielTlNevada batholith: Science. '1.158, p. 14071417.Burchfiel, B.C., and Davis, G.A., 1972, Structural framework and evolution of the southern part of the Cordil leran oro8eny,western United States: AmericanJournal ofScience, 'I . 272, p. 97-118.Burchriel, B.C., and Davis, G.A., 1975, Natureand controls of Cordilleran orogenesis,western United States-extmsions ofan carlier synthesis: American Journal of Science,'I . 275-A, p. 36l-396.Burchfiel, B.C., and Davis, G.A., in press, Mojave Desert and environs (Chapter 9) inErnst, W.G., Editor,Thegcotectonicdevc!.epment of Califomia (W.W. Rubey Volume No. I) : Prentice Hall.Crouch, J.K., 1979, Neogene tectonic evolutionof the California continental borderlandand western Transverse Ranges: GeologicalSociety of America Bulletin, v. 90, p. 338",.Crowell, J.C., 1974, Origin of late Cenozoicbasins in southern CaUfornia: p. 190-204 inDickinson, W.R., Editor, Tectonics andsedimentation: Society of Economic Paleontologisu and Mineralogisu, SpecialPublication No. 22, p. 190-204.Crowell, J.C. 1975, The San Andreas fault insouthern California in Crowell, J.C., Editor, San Andreas faull in southern California, California Division of Mines andGeology, Special Report 118, p. 7-27.Davis, G.A., 1969, Te


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Huel, 0., and Dillon, J., 1978, The PelonaOrocopia Schist and Vincent-ChocolateMountain thrust system, SQuthern California in Howe!, D.O., and McDougalL K.A.,&lilon, Mesozoic paleogeography of Ihewestern United States: Pacific Section, Scciety of Economic Paleontologists IUIdMinera1ogists, Pacific Coasl Paleogeography Symposium 2, p. 453-469.Hopson, C.A., Mattimion, J.M., and Pessagno,E.A., 1975, Record of Late JUr&S$ic seafloor spreading, California Coasl Ranges:Geological Society of America, Abstractswith Programs, v. 7, p. 326.Howell, D.O., and Vedder , J .O., 1978, LateCrelaCCOus paleogeography of the Salinianblock., California in Howell, D.G., andMcDougall, K.A., Editors, Mesowicpaleogeography of the western UnitedStates:Society of Economic Paleontologistsand Mineralogists , Pacif ic Coast Paleogeography Symposium 2, p. 107-116.Howell, D.G., and Vedder, J .G., in press,Struetunl implications of stratigraphic discontinuities across the SQulhem Californiaborderland (Chapter 16) in Ernst, W.G.,Editor, The geotectonic development ofCalifornia (W.W. Rubey Volume No. I) .Invin, W.P., 1960, Geologic reconnaissance oftbe northern Coast Ranges and KlamathMountains, California, with a summary ofthe mineral resources: California Divisionof Mines Bulletin 179, SO p.Invin, W.P., 1972, Terranes of the western Paleozoic and Triassic belt in the southernKlamath Mountains, California in Geological Survey Research, 1972: U.S. GeologicalSurvey Professional Paper 8OO-C. p. CI03CIII.

Irwin, W.P., 1977, Review of Paleozoic rocksohhe Klamath Mountains inStewart. J.H.,Stevens, C.H., and Fritsche, A.E., EditOl'$,Paleozoic paleogeography of the westernUnited States: Pacific Section, Society ofEconomic Paleontologists and Minera1ogists, Pacific Coast Paleogeography Symposium I, p. 441-454.Irwin, W.P., Jones, D.L., and Kaplan, T.A.,1979, Radio la ri ans from pre -Nevadanrocks of the Klamath Mountains, California and Oregon in Howell, D .G ., andMcDougall K.A., Editors, Mesozoic paleogeography of the western United States: P.cific Section, Society of Economic Paleontologists and Mineralogists, Pacific CoastPaleogeography Symposium 2,p. 303-310.Irwin, W.P., Jones, D.L., and Pessagno, E.A.,Jr. , 1977, Significance of Mesoz.oic radiolarians from the pre-Ne ...ad&n rocks ofthe southern Klamath Mountains, California: Geology, v. 5, p. 557-562.

Jacobson, MJ., 1979, Petrologic variations inFranciscan $IUIdstone from the DiabloRange, California in HowclJ, D.O., andMcDougall, K.A.,Editors, MCIOZOic paleogeography of the weslem United StaleS:Pacific Section, Society of Economic Paleontologists andMinera1ogbts,PaciticCoutIPaleogeogn.pbySymposium2, p. 4 0 1 ~ 17.Jennings, C.W., 1977, Geologic Map of California, Scale 1:7SO,CDl: California Divisionof Mines and Geology.Jones, D.L, Blake, M.C. , Jr. , Bai ley, RH.,and McLaughlin, R.L., 1978, DistributionoflateMesozoic mlianges along Ihe Pacific

Coast of North America: Tectonophysics,v. 47, p. 207-222.Jones, D.L., and Irwin, W.P., 1971, Structuralimplications of an offset Early CTetaceousshorcline in northern California: Geological Society of America Bulletin, v. 82, p.glS-822.Kamerling, M.J., and Luyendyk, B.P., 1977,Tectonic rotation of the Santa MonicaMountains in soutbem California: Ame:rican Geophysical Union Transactions, v. 58,p. 1126 (Abstract).

Kamerling, MJ., and Luyendyk, B.P., 1979,Tectonic rotations of the San ta MonicaMountains region, western Transverse:Ranges, California, suggested by paleomagnetic vectors: Geological Society of America Bulledn, v. 90, p. 331-337.Kistler, R.W., Evemden,J.F., and Shaw, H.R.,1971, SielTll Ne:vada plutonic cycle; Part I,Origin of composite granitic batholiths:Geological Society of America Bulletin, v.82, p. 853-g6g.Kistler, R.W., and Peterman, Z.E., 1973,Variations in Sr, Rb, K, Na and initialll'lSr/

IJSsr in Mesozoic granitic rocks and intrUd.ed wall rocks in central California, Geological Society of America Bulletin, v. 84, p.3489-3512.Lanphere, M.A., 1971, Age of the Mesozoicoceanic crust in the California CoastRanges: Geological Society of AmericaBulletin, v. g2, p. 3209-3212.Menard, H.W., 1964, M.rine geology of thePacific:McGraw-HillCo., NewYork,271 p.Miller, CF., 1977, Early alkalic plUlonism inthe cale-alkalic batholithic belt of California; Geology, v. 5, p. 685-688.

Miller, CF., 1978, An early Mesozoic alkalicmagmatie belt in westemNorth America inHowell, D.G., and McDougall , K.A., Editors, Mesozoicpaleogeography of the: westem United States: Pacific Section, Societyof Economic Paleontologists and Mineralogists, PaeificCoast PaleogeographySymposium 2, p. 163-187.Page. B.M., 1978, Franciscan melanges compared with olistostromes of Taiwan and Italy: TectonophysiC$, v. 47, p. 223-246.Page, B.M., in press, The soulhern CoastRanges (Chapter 13) in Ernst, W.G., Editor, The geotectonic development of California (W.W. Rubey Volume: No. I) .Parsons, Barry: and Sclater , J .H., 1977, An,analysis of the variatm ofocean floor bathymetry IIDd heat flow with age: Journal ofGeophysical Research, .... 82, p. 803-g27.

Pessagno, E.A., Jr., 1973, Age and significanceof radiolarian chcns in the California CoastRanges: Geology, v. I, p. 153-156.

Poole, F.G., and Sandberg, C.A., 19n, Mississippian paleogeography and tectonicsof thewestern United Stales in Stewart, J.H., Stevens, C.H., and Fritsche, A.E., &li1Ol'$, Paleozoic paleogeography of the westernUnited States: Pacific Section, Society ofEconomic Paleontologists and Minera1ogists, PacificCoast Paleogeography Sympo-sium I, p. 67-86.Saleeby, J.B., 1978, Kings River ophiol it e.southwest SierTll Nevada foothills, California: Geological Society of America Bulletin, v. 89, p. 617-636.Saleeby, J.B., 1979, Kaweah serpentinite me..lange, southwest Sierra Nevada foothilb,

California: Geological Society of AmericaBulletin, v. 90, p. 29-46.Saleeby, J.B., Good..-in, S.E., Sharp, W.O., andBusby,CJ., 1978, Early Mc:sowic paleotectonic-paleogeographic reconslruction ofthe southern SiClTa Nevada region in Howcll, D.G., and McDougall, K.A., Editors,Mesowic paleogeography of the westernUnited States: Pacific Section, Sociely ofEconomic Paleontologists and Mineralogists, Pacific Coast Paleogeography Symposium 2, p. 311-3l6.

ScholL D.W., and Vallier, T.L., 1979, Tectonicerosion al a convergen l margin, a mechanism that could have contr ibuted to thetruncation of Cordilleran geosynclinaltrends: Geological Society of America, Abstracts with Programs, v. II , p. 126.Schwcickert,R.A.,andCowan,D.S.,1975,EarlyMesozoic tectonic evolution of the westernSierra Nevada,California:Geological Society of America Bulletin, '0'.86, p.1329-1336.Silver, L.T., and Anderson, T.H., 1974, Possible lef t- Ia lera l ear ly to middle Mesozoicdisruplion of the southwestern NorthAmerican craton margin: Geological Society of America, Abstracts with Programs,v. 6, p. 955.Silver, L.T., McKinney, C.R., Deutsch, S., andBolinger, J., 1963, Precambrian age: determinat ions in the western San GabrielMountains, CaJifomia: Journal ofGeology,v. 71, p. 196-214.Stewart, J.H., 1972, Initial deposits in Ihe Cordilleran geosyncline-cvidence of a late Precambrian gSO m.y. ) continentalseparalion: Geological Socic:ly of AmericaBulletin, v. 83, p. 1345-1360.

Stewan, J.H., 1978, Basin-range structure inweslem North America-a reviC'N: in Smith,R.B., and Eaton, G.P., Editors, Cenozoictectonics and regional geophysics of thewestern Cordillera: Geological Society ofAmerica Memoir 152.Stewart, J .H ., and Poole, F.G., 1974, LowerPaleozoic and uppc:rmost PrecambrianCordilleran miogeocline,Great Basin,western United States in Dickinson, W.R.,&li_tor, Tectonics and sedimentation: Societyof Economic Paleontologists and Minera1ogists, Special Publication No. 22, p. 23-57.Stewart, J.H., and Suczc:k., CA., 1977, Cambrian and latest Precambrian paleogeographyand lectonics in the VfCStem United Statesin Stewart , J .H., Stevens, C.H., and Fri tsche, A.E.. Editors, Paleozoic paleogeography of the western United States: PacificSection, Society of Economic Paleontologists and Minera1ogists, Pacific CoastPaleogeography Symposium I, p. 1-11.Suppc. John, 1972, Interrelationships of highpressure metamoll)hism, deformation, andsedimentation inFranciscan tectoniC$,USA:24th International Geological CongTCSS,Montreal, Reports Section 3, p. 552-559.

Windley, B.F., 1977, The evolving continents:John Wiley &; Sons, NC'N York, 385 p.Yeat s, R.S., 1969, Rif ti ng and rafting in thesouthern California borderland in Dickinson, W.R., and Grantz, Arthur, Editors,Conference on Geologic Problems of theSan Andreas F.ult System, Proceedings,Stanford, California, 1967: Stanford. University Publications in Geological Sciences,vol. 11, p. 307-322.

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C'l,et tn d CQun"es lI11eCled bv p,opoHld nllw Of,evlsed SpeClel Slud,es Zooet tl'lOWO 00 p.elimin v ' .Vlew mllps o f Julv I. 1979

Thi rty new revised Special StudiesZones.ups were issued by the CaliforniaDivision of Mines and Geology on July I,1979. These nups were distributed to thealTocted c i t ~ , counties,and Slateagcnciesfor preliminary review. Cities and count review th e maps and submit comments to the State Mining and GeologyBoard. Revisions are nude where warranted. The official maps will be issued bythe Slate Geologist on January I, 19S0.

,,"10 zo :50 WILESI I 'o,

-, .... " AIba.h,. " ~ , Y O I ' ~ LJnde " EI.."" ,e n E:enhquek. v -V, Ptll


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1977 1978CALIFORNIA MINING REVIEW

Thelol low,ngUKcerptsaretakenlrom MINERALS IN THE ECONOMY OF CALIFORNIA. Slate Mineral Profile 1979. byJohn McWilliams, Slate Liaison Ofheer, U S Bureau of Mines: James F DaViS. State Geolog,st. California DiVISIon o f M in es and Geology:and William B. Clalk, Geologist. Cali fornia Division 01 Mlnesand Geology. SMP wa s pub li shed by the BUfaau of Mines. U.S. Departmentof the Interior. in cooperation with California Department of Conservation. ,Editor

A total of 34 non-fuel mineral commodities are produced in California (tables I and 2). California leads the nationin the production of asbestos, boron, Portland cement, diatomite, sand and gravel,rareearths. and tungsten. It is third in theproduction of crude petroleum and is amajor source of natural gas, salt , clay,stone, magnesium compounds, sodiumcompounds, gypsum, iron ore and talc.

MINERALS PRODUCEDNon-Metallic MineralsExcluding natural gas, natural gas liquids, and crude petroleum, mineral production in Cali fornia increased 6% in1978 to reach $1.4 billion and rank thirdin the nation. Cement was in the lead with32% of the total value. Boron, with 19%,

and sand and gravel, with 18% of thetotal mineral value were next. These threecommodities aecount for $%3 million or69% of the total mineral value and 94%of the increase in value in 1978.Production of cement declined 282,000Ions (3%) in 1978 but ils overall valueincreased 10% to $445 million because ofhigher unit value. Production of boronwas up 4% to 1.5 million tons and itsvalue was up 10% to $260 million. Sandand gravel production remained essentially unchanged (up less than 1%) and value was up only slightly (2.8%) to $258

million.Other significant changes in non-metallic mineral commodities include asbestos, which declined 10% in quantity and5% in total value, and lime, which decreased 13% in quantity and 20% in value. Feldspar, l i thium' compounds,magnesium compounds, sodium carbonate. sodium sulfate, clay, diatomite, gypsum and stone all declined in quantity butonly lithium compounds, feldspar. and sodium sulfate declined significantly in val-

ue. Non-metallic minerals comprise 90%of the total value of non-fuel mineral production in California. Preliminary production data for oil and gas show a sl ighldedineofO.6% and 1.3% respectively according to the California Division of Oiland Gas.Metal l ic Minera ls

The important metal lic minerals areiron ore. which declined in production in1978 but maintained its ovcrall value; molybdenum. which declined sharply in production but increased substantial ly invalue; tungsten. which increased stronglyin quantity but only slightly in value; andrare earths which increased in both quant ity and value. These four minerals comprise 99% of the value of metallic mineralproduction or $138 million.Gold declined 20% in production butregistered a 4% increase in total valuebecause of higher unit prices. In 1978, silver increased 5% in quantity and I I % invalue compared with 1977. Copper increased 18% in quantity and 17% in value over 1977.

Oil and GasCalifornia continues to be a majorsource of oil and natural gas (table la).Oil was produced from 234 active fields in

16 counties at a rate of more than onemillion barrels per day. Approximately50% of thestate's total oil production wasfrom Kern County. During 1978 combined State and Federal.off-shore fieldsaccounted for 17% of the oil and 7% ofthe natural gas produced in California.Most of the State off-shore productioncame from the Wilmington and Huntington Beach fields. All of the Federal offshore production came from Carpi:nteriaand Dos Cuadras fields. About 50% ofthe natu ral gas production in 1978 wasassociated with oil production. The restcame from natural gas fields largely

(95%) located in District 6 which comprises the area north and eastof San Francisco Bay. In 1978, 313 billion cubic feetof natural gas were produced, a decreaseof 1.3% from 1977.

GOLDTroy Gold Industries of Alberta, Can

ada, reopened Ihe Blazing Star Mine inthe Mother Lode country near WestPoint , Calaveras County. Up to 165 tonsof ore per day can be processed by thecombination gravity and notation mill toyield I to 1.5 ounces' of gold per ton.Tungsten, copper, and silver arc also produced. The mine was first located in 1857and worked in the oxidized zone to adeplh of 400 feet.

GEOTHERMALRESOURCESUnion Oil Company of California reportedly has proven geothermal reservesequivalent to 165 million barrels of oiL

The company is operator and half ownerof The Geysers operation in northernCalifornia, the only commercial geothermal operation in the UniledStates and thelargest in the world. The steam is used byPacificGas and Electric to power 12 electrical generators with a 10lal capacity ofmore than 500,000 kilowatts. The cost ofgeothermal sleam purchased by PacificGas and Electric at TheGeysers increasedfrom 14.18 mils per kilowatt hour to 16.02mils per kilowatt hour but remains thecheapest sourceof energy for PO &E otherIhan hydro-electric power. For comparison, electrical energy from oil costs 45mils per kilowatt hour. Geothermal energy provides 6% of the electrical energyused by the company 's 5.7 million customers in northern and central California.The tOlal Geysers project is expected toeventually achieve a capacilY of 2 millionkilowatts.

'98 california Geology September 1979


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Addi tional sites drilled and tested byUnion Oil Company of California are inthe Brawley area in the Imperial Valleywhere the company has agreed to sell geothermal energy to Southern CaliforniaEdison. The power company will build al(),OOO Kilowatt generating plant to beginoperation in 1981. This plant will test tbeeconomic and technologic feasibility ofusing the highly corrosive hot brines forgenerating electrical power. If successful,the agreement could lead to constructionof as much as 460,CKlO kilowatts of capacity. Other geothermal test sites in the Imperial Valley include the Sallon Sea in thenorthern section and Heber in the southern section.

COAL RESOURCESCa1iornia has insignif icant coal resources of its own but anticipates that asmuch as 15% of its energy needs may be

provided by coal by 1990, up from the6%presently supplied, according 10 the StateEnergy Commission. Two applicationsfor coal-using plants arc presently beforethe Commission: the Pacific Gas andElectric plant in northern California and

Southern California Edison Company'sCoal Gasification Project. in SanBernardino County. ThiI 5-ycarpiJot. project will'testla, processdevelopedby Teuco, Inc., to produce non-polluting gas from coal to be used directly in Southern California Edison'selectric power generating plant at Daggett, 12 miles east of Barstow, California.MINERALS IN THE

ECONOMYEmployment in the mining industryaveraged 37,000 in 1978, includingoil andnatural gas workers, earning a total of$687.7 million. The average annual wagewas S18,587. About 0.4% of the State's

non-agriculturallabor force is employedin mining. The average hourly wage wasdown 19% from 58.86 to 57.18, and average weekly earnings were down 9% from5373.01 to S34O .33 in 1977. Averagehours of work per week increased from42.1 to 47.4.

With nearly half (43%) of Californialand under Federal ownership, revenuefrom mineral and oil and gas leases is sub-Table I. Minera l Product ion in California

stantial. In 1978, mineral leases on Federal land returned over $2.9 million inroyalties. On-shore oil and gas leases returned $16 million in royalties from oiland $4.5 million from natural gas. OfTshore oil and gas leases re turned SI1.7million in oil royalties and over $314,000in natural gas royalties. There was nocommercial production of goothermal energy from Federally leased land in 1978.The State collects rents and royalt iesfrom mineral, oil and gas, and goothermalleases on State-owned lands and on landsfor which the mineral rights are reservcclin whole or part to the State. For the period ending June 30, 1979, mineral anddredging.royalties to the Stateareestimated to be S339,500, oil and gas royalties areestimated at 587.2 million, and royaltiesfrom geothermal energy at $4.3 million.

The latter funds are placed in a trust fundpending the outcomeof litigation to determine ownership of geothermal energy. Atissue is the question of whether it shouldbe regarded as a mineral with ownershipby the mineral-rights holder, or as waterowned by the holder of surface or waterrights. At the Federal level, geothermalenergy is regarded as a mineral.

Min...1"'_"0.B",on 1.4,,,,,,.,......C."",nlM . P",tlo......_.,Cloy. .

C""p. , 1'10 oont.nl ot 0' ' ' . "0.)Oi.,,,,,,i, , .G.m S,on .Gold I ,""O l>Ie oon'.nl ot ",. . . "0 IGyp ,.,1.0 (, .oo....bItI oon' .n ' 01 ", . . . "0 I,-M.,ou, ..Pumio.S."" . .., G' I.SI ....' I , .oo blo oon' .n ' 0' ", .. . "0 ISu",.C'u ...."O'm."",o" ..hlc: ..._

Zinc: ('00"".,.1>10 oon,."l ot ", . . . "0 IComb'. . . . . . .Iu . 01 o.lc:,um ohl",id. O"bon diox"' I.ld . . . .,. ~ o " " . W"um oompo,,,,,, m. g ....

....m oompound. molybd.num. 1'00" p.'IU. phosph., . 'oot ('9771. po . . . . .um .. II.. "''''. . . 11, m.,.1 oono'n". ' ' ' . " " . """"um eo,bono'., """,oum .. .It.'. 'ung",,,, oonc.nll. , ""i ' .m. indio.,.. . by Symbol W

To'"

on"" 'o n.th"", .."" ...."" lOn' ..0 0 .00 .....o , t ' on.'h""..nd ... .ort 'O/l' .. ."oy""ne.. ,.til""'. ." " oh"" 'o n. ....."" 'Onl .lh.,.... "" ....", 1 lO/l.7&-1>"""" '11.1:0 ...t i l"". ." " ""on 'Onl ..00'h"",.." " troy "",noIh.,...."" ....", t Ion.do _....""",I ,on.00

1917 '978 piOu.n"ly Vllu. OUln",y V.lu.Ilhou..""11 (thou.""11

76.207 HUn A .m t1.cl2,- ~ ' u.w w w W9.271 _.,as .- -.., . 11.7'" 2.016, 13"28"' ,.., O - ~ "4 "4.. - . '.m .= , . .=, ,- 21.0'11 m ,9.1,9w W- , ...,011.138 ~ $ ,- 2S8.(XX1A ., .,

:l.Iml lIO.loI6 ~ . ~ , o o" - ,=.. "n 109.816 .-, ,241. '33

1.-ooo.'1!;gI' P limln.. y. Nil. No ' , I .b" W W,'hlHlld '0 o'" lO I P,oduotlon m. . . . .'fI" by m,n. "'' 'pmfln,., .. I. . . ", ml,tl"blo p.oduotlon I 'fIO"'ding con..,mp'io" by p.oduo.'11Table ". Oi l and G as PrOduction ,n California '

1971 1976"C,ud. 0,1 N.,u,.1 G..On_ohor. 'hou .."" 12 s.lIon 1>1I. . . . . 266.965 m.= On_ohor. m.lhO/l cubic I..'Olt_...." , . OU_....O,.S,.,. 00 11I,196 15.000 S,.,. 00F. . . . . . I 00 12.3lXl "..... FOd ...1 00

ro,.1 00 :l.I9.161 ~ ..... To'" 00

"17297,76711.237.

3'1.100

19711"

313.200 1976 Clhlo' ' ' ' . 0.1.""G.. P,oduc,.on S,." ...C. "" " N.w ",.n Op... "on. p,.lom'n.. y ' . 1 '0" , PubloCI'oon No PAOJ.1A.."",c.. "'S"""Y 01 C.IoI"'",". Oeplrtmon, 01 Conso, l,on"P,elom'nI'y. F,g",......."me ' " b.. .d on nine mon,h. 01 l"O,,,.o,,on

California Geology september 1979 199


15/23

Table :t Mineral Production. Counties 01 California. 1977

COMMOOITY OUA",T'TY VALUE C.m.n' 2.042.(100 ....cw, ,,,,,. $81.2lli5.OCOI th"" .. ndol C ~ __ ~ " "'or, ,,,,,. __ $2.31'.(0)Al..A""IU\ 0"'0"';'.C..,..__....__ ... """ "'0" '0'" ._, ~ ' ' ' ' ' Cyp"",,", ........_.._..._.-~ ' "mic . ''''' IIftCW1 ,an.Sand .n d C vP u 'FIIUNO PumlCo '""" "'ort 'on. I'2UIXIA_" , o l S."" Ond G....... """ ......, 'on. m"""."


16/23

PLUMAI ,,- . ~ " " . . .. . , t o n._ -""G _ ." .............._..- Tolo'Soo"" ." " G. . . . . ' ="" _tton.. 547t.lXXl . . . .IITA CflUZ5_ . C. . . . ." ,,,- .. ,............................


17/23

Summary of Activities

STATE MINING AND GEOLOGYBOARD REPORT

California Desert ConservationArea (CDCA)The Board visited the Barstow area inApril 1979 to observe the potential formined lands reclamation in the desert.Two operating mines (NL industries'Hectorite mine and the Blue Star goldmine) and American Smelting &RermingCompany's Waterloo Project, low-gradesilver deposit were toured. Operators atthese sites discussed future reclamationplans with the Board. Visual impacts,dust generation, and reestablishment of

vegetative habitatappeared to be the principal reclamation-related problems associated with these operations.Following the tour, representativesfrom the U.s. Bureau of Land Management discussed the Bureau's COCA studyin a Mineral Resource ConservationForum convened by the Board. Representatives from industry and from local,state, and federal agencies participated inthis discussion.The COCA study will provide recommendations for federal land-use decision

making in the desert, an area comprisingone-fourth of the state, and known for itshigh recreation and environmental valuesas well as great mineral potential . TheFederal Land Policy and ManagementAct of 1976 requires that this study becompleted and in the hands of Congressby September 30, 1980.The Board is concerned that information on the mineral potential of theCOCA is not commensurate with thescope of pending land-use decisions bythe Federal Government. In cooperationwith the Division ofMines and Geology,the Board is seeking ways in which thestate can make available timely and effective infonnation on mineral potential ofthe desert to the Federal Government.The BLM was unable to offer muchenlightenment in response to Board questions on the effects of particular landmanagement policies on mineral resourcedevelopment. Of particular concern wasthe effect ofwilderness designation on thedevelopment of adjacent mineral depositsand whether the maintenance of certain

environmental standards in wildernessareas, particularly those connected withair pollution, would require similar standards in proximity to wilderness areas.Such standards could prevent miningeven though the mining activity is outsidethe wilderness area.San Fernando Valley ClassificationAt the May 2S, 1979 meeting, theBoard accepted from the State Geologist

the first formal report on mineral landsclassification. This report, entitled "Minerai Land Classification of the GreaterLos Angeles Areas: Parts I and li", identifies sand and gravel deposits, andprojects SO-year needs for these mineralresources, in theSan Fernando Valley Region. Other regions in the Los Angelesarea will be classified in subsequent re-ports by the Division of Mines and Geology.

This report is precedent setting both inits content and scientific rationale. I t isthe fU'St formal mineral lands classification under California's Surface Miningand Reclamation Act, and thus establishes the methodology for future classification programs. I t represents the firststage of the Act's classification-designation process which is a unique approachto the conservation and development ofmineral resources through stale and localcooperative planning efforts.Ventura Coun ty ClassificationPriorities'The Board revised its classification priorities to move coastal Ventura Countyfrom Priority 3 to Priority I under urbanareas. This action was taken in response topending land-use decisions which threaten the availability of aggregate resourcesin the area.Ventura County is faced with a oneyear deadline for completing an Environmental Impact Report. which is requiredbefore conditional use permits can be issued to sand and gravel operators in thelower Santa Clara River of coastal Ventura County. This area supplies about90% of the sand and gravel for the Ven

tura-(hnard area. Ventura County Flood

StataMining and Geology Board ChairmanRobert H Twissl on right} and Board mem-ber Raymond Krauss I center) watchingRay Lint 's technIque lo r separat ing goldlrom are coneentrates produced f rom h isB lu e S tar m in e in the CaliCO Mountains.San Bernardino County

Control District restnctlons on diggingdepths make it necessary to allow aggregate mining in areas outside the river'sflood control channel or to import sandand gravel to assure a continued supply ofconstruction aggregate.TheCountyofficials and aggregate producers, as well as the State Geologist, feel

that the classification of this area isessential for assessing existingre:serves and locating new aggregateresources.For information on the Board's monthly meetings and other activities, contactDouglas W. Sprague, Special Representative, Department of Conservation, Room1327, Sacramento, California 95814,(916) 322-1082....DouglasW.Spraguc.

2" California Geology September 1979


18/23

Condensed from a speech presented to the California Seismic safety Commission by Bruce A. Bolt on April 27.1979. Dr.Boll is the Directorof the Seismographic Station at the University of California. Berk.eley.

REASSESSINGTHE EARTHQUAKE HAZARD

IN CALIFORNIAByBRUCE A. BOLT. CommissionerCalifornia Seismic Safety Commission

There are a number of connictingstands and interests that go into reassessing the present earthquake hazards inCalifornia, such as the improved construction of public schools and hospitalsas opposed to the multiplicity of designsand materials of new structures. Theseconflicts become more difficult to quantify as the populat ion continues to growand society becomes more complex. Thereare two seismological aspects of these conflicting ingredients of risk evaluation.Thefirst is the earthquake occurrence probability itself, lind the second is the preparedness of California to respond effectively to an earthquake when it occurs.

EARTHQUAKE OCCURRENCEPROBABILITYWe must now say that t ime is runningout so far as the next big ear thquake ofmagnitude 7 or greater is concerned. Thelate Professor Perry Byerly, my predecessor at Berkeley, said that when he first

had the job of keeping track of earthquakes in northern California he neverclosed the door of his garage. He felt thatperhaps any night the next great earthquake in the Bay area would come and hewould have to hop into his car. and godown to the University and lead the studies of its af termath. But when the earthquake had not come after 30 years heclosed the door of his garage. In the 16years since I have been at the Universityof California, there has been no greatearthquake in California and for variousreasons, each year, it has seemed appropriate to think of an occurrence in thenext 10. or 20 years.We can no longer keep pushing thistime window forward for a number ofreasons. The evidence now is much stronger than 30 years ago or even\16 yearsago that a large earthquake is imminent.

EARTHQUAKE EVIDENCEHistorical Record

The first line of evidence comes fromthe historical record. In the last centurythere were a number of very large earth-

quakes in California. There was a largeearthquake in 1836, centered on the Hayward faull. Fromwhatwe know thesedays,it would probablybec1assed as"great". Anearthquake in 1838 was felt strongly inSan Francisco. It opened a great crackmany miles in length along what is nowcalled the San Andreas fault.In 1868 there was again an outstandingearthquake on the Hayward fault alongthe base of the hills to the east of SanFrancisco Bay. This earthquake produceddestruction in San Jose, Hayward. anddowntown San Francisco. Until 1906 itwas referred to locally as "the great earthquake". A group of laymen got togetherand wrote a report on that earthquake,but the report seems to have been supressed because no copy has been found inthis century. However. in 1906 some persons who had gone through the 1868earthquake were asked to give their recollections - these will be referred to later.And then there was the great earthquake of 1906, with no major rupture ofactive faults in northern California sincethat time. In southern California thegreatFort Tejon earthquake occurred in 1857,and apart from the Kern County shock of1952. again there has not been an earth- .quake of major size near metropoli tanareas for more than 100 years.Tectonic MovementSecondly, the geodetic survey that hasgone on in the San Francisco Bay area forabout a century and a half indicates thatthe Farallon Islands, Mt. Tamalpais. andMI. Diablo continue to move relative toone another a t a rate comparable to thaIobserved prior to the 1906 earthquake.The Farallon Islands are moving northrelative to MI. Diablo at the rate of about2 inches a year and there can be no doubtthat strain is building up in the crustalrocks like the tightening of a watchspring. The level of strain that wasreached prior to fault rupture in 1906 isknown from geodetic measurements ofthe last century, and a comparison suggests that a sudden slip will have to occuralong one of the main faults in the area torelieve the present strain before too long.

PaleoearthquakesThirdly, trenches recently excavatedacross the San Andreas fault in southernCalifornia have revealed evidence of pastgreat earthquakes. The liquifaction effectsof paleoearthquakes have been preservedin beds of sand and peat. They indicatethat the average recurrence interval ofgreat earthquakes on the San Andreasfault in southern California is aboul 200years - sometimes more, sometimes less.This recurrence interval extends back atleast one thousand years. Therefore. giventhe t ime that has elapsed since the lastgreat earthquake, we should. as a workinghypothesis, expect a great earthquakesomewhere in California within the next10 years. The odds are about even thatthis will be the case. and for every yearthat goes by now these odds will growsteadily.

If more specific earthquake predictionscould be made they would help in preventing loss of life from collapse of structures. but seismology has not yetadvanced to the stage of practical preciseearthquake forecasting. Even i f validearthquake prediction were possible, thehazard to vulnerable buildings in California, and the resulting economic loss,would remain.EARTHQUAKE PREPAREDNESSThe need to reduce earthquake hazardsmust be balanced against other social demands. The effort to mitigate againstearthquakes must be expressed in terms ofj eopardy to life and cost benefit so thatpeople can make reasonable decisions on

what is an adequate level of earthquakesafety for society.Consider the two words "earthquakerisk". An equation between the occurrence of great earthquakes, and the riskthey produce must be considered. Asteady state situation in California shouldbe the goal. The steady state situationwould be one in which the citizens,through the tax base, allocate a certainamount of resources toward maintainingthe status quo of adequate earthquakepreparedness. In other words, the pUblic

California Geology september 1979 '03


19/23

must accepl thai af ter preparal ion at alolerable level is reached, it must be sus-lained economically for many years.There is sti ll a long way to go in tenos ofindividual, state and corporate etTort, education, and expenditure of funds, beforeIhis steady stale is reached.Much is now known about earthquakesand about how to reduce earthquakedamage. This knowledge must be transferredquickly. There has been progress in thestudy of ground motion itself over thepast 10 years. In engineering design therehas been advancement in ways to handlethese seismic forces. Presumably thechanges in building codes have significantly improved them. There is now morehelp from theFederal governmenl underIhe Earthquake Hazard Reduclion ACIwhich is designed 10 reduce Ihe risk o f lifeand property from future earthquakes.The establishment of the Seismic SafetyCommission in California has brought together often very disparale kinds of intereslS fbus stimulating more etTeclivemitigation activity and needed legislation.Recent DamagesDespite advances in earthquake studies, substantial losses have occurred inrelalively small earthquakes over the lastfew years. The Santa Barbara earthquakeof August 13, 1978, was a relatively smallearthquake (M 5.6) The strong groundmotion in this earthquake lasted 2-3 seconds and shook only a restricted area, yetil caused up to 57 million damage to property. Fo r comparison, the strong groundmotion in the great 1906 earthquake lasted 40 seconds. The amount of energyreleased was spread over much o f coastalCalifornia, and was at least one thousandtimes greater than in the Santa Barbarashock.In the 1978 Santa Barbara earthquake65 people were injured by falling objectsand glass. Damage in the earthquake included a number of buildinp built after1952, Ihus disputing the concept that onlyold buildings from another era should beconsidered when assessing earthquakedangers in California. Reports from th eUniversity of California at Santa Barbaraoutlined cases where the building codewas not followed and errors seemed tohave been made in construction. Thesefacts raise questions about proper inspection during construction ofboth state andprivately owned buildinp in California.Public Awareness

If a small magnitude 5.6 earthquake isable to produce significant destruction ina limited area, what is to be done to prepare for a great earthquake? Fir sl, detailed re-examinalion of earthquake riskin California is needed. We need a broader

framework than the one used in th e past- a framework thai will consider earthquakes in relation to the whole economicsystem. We mUSI detennine how buildingcodes are being applied. how communitiesar e responding 10 suggestions to preparefor earthquakes, and particularly we mustassess the cost benefits thai can accrue byproperly carrying oul earthquake mitigalion plans. Expendilure of public fundsmusl be fully justified and clearly efficienlin order to achieve a steady state withinthe next few years.We musl delve more deeply into emergency preparedness Ihan we have in Ihepast. Although th e speclre of added expense is often used as an excuse for inaclion, much can be done within areasonable cost. So often when dealingwilh specific groups and siluations,progress can be made by people al grassroots level ifIhey only know whal to do.

Today there are more people concernedabout earthquakes in the communily thanIhere were a few years ago. Quile apartfrom governmenl plans, communitygroups are coming together at Ihe locallevel to eKamine such queslions as:What canwe do in thisparticular neighborhood ifa big earthquake occurs (onIhe Hayward fault, or on the San An dreas fault)?What can we do before the nexl earthquake to see whal hazards can be reduced?- Will adequate fire fighting facilities beavailable in Ihe area after the ear thquake?

Tb e Seismic Safety Commission,Ihrough its Earthquake Education Commiltee, and other groups can encouragethis grass roots activity IhroughoUI thestate. The Universi ty of California atBerkeley had an "Earthquake AwarenessDay" on April 18, 1979. In Ihe course ofplanning this program there were manymeetings of administrative officers, clerical statT, laboratory managers, officials involved in environment, health and safely,and representatives from student groups.The committee met regularly wilhout alag in interest. Apparently there isa desirefor specific infonnation aboul just whalwill happen when another great earthquake occurs.California is fortunale to have exlensiveeye wilness accounts of some of the bigearthquakes. These kinds of reports helpa greal deal to educate the public. Thefollowing accounts describe the 1868earthquake on the Hayward Fault as ilwas in San Leandro:Report #1:

1 managed 10 get out of the building in San leandro when the shakingstarted. The house was thrown from

its foundation. Ihe chimneywas tornfrom the roof. the the porch waswrenched away. dishes were broken. and everything was in contusion. I found thaI most of Ihe houseswere in Ihe same condition as myown-Ihrown from their foundations. with chimneys down. porchesknocked sideways. elc. All the whiletheground was shaking and continued to shake for days. evenweeks:

Report #2:"I was then about 15 years of ageend my home was near Irvington.When the shock came Iwasalone inthe house with my baby brother andmy mother called to me to get thebaby. I mal\8ged to get the childover my arm. lace down with a pillow on top. then falling and crawlingI worked my way to Ihe kitchendoor. My mother wason the ground.and every time she tried 10 get upshe was thrown a9ain. As I sat thereIcould se e the ground in waves likethe ocean. After the main shock Ithink we had a hundred shocks duroing the first 24 hours. not a housewas left with a chimney on it. Thepiano was out of the room and thesafe had broken through the wall:Such direct, unediled infonnation givespeople a chance 10 reassess what Iheythought they were going to do when thegreat earthquake occurred. Some peopleassume Ihey willmake emergency calls on

th e lelephone, and some people think theycan gel in Iheir car a t work and go hometo their families! They are probably nOIgoing 10 be able to do such things. Thereis a gap between whal will be possible andwhat people think they are going to do.That is one of the uncertainties thai goesinlo the reassessment of what Ihe consequences of the earthquake are going to be.

EARTHQUAKE DEFENSEA very important componenl in tryingto reach th e sleady state in a relatively

shon lime is to have more earthquakeeducation. We must get the allention ofth e whole California populalion and describe what Ihe earthquake experience isgoing to be like, so thai each person willbe able to respond in a sensible way. Wehave 10 think about whal will happen onevery level in anolher greal earthquake.More assistance must be given 10 localcommunity groups so that they can takeaction themselves to assist in fire fighting,first aid, and home safety procedures. Asa consequence, the public may givestronger support for Ihe expenditure of asmall part of the overall California budget10 reduce th e earthquake risk. Let us inthe next five years move earthquake riskequation toward Ihe sleady stale of minimal risk, for time is no longer on ou r side.

'" California Geology September 1979


20/23

COUNTY REPORTS

PRELIMINARY REPORTS

SPECIAL PUBLICATIONS

MISCELLANEOUS PUBLICATIONS

Compllauon o f s trong -mot lon fecords recoveredfrom th e Santa Barbara eatlhquake of 13 Augusl1978 $1.00Processed data from the parlial Slrong-mOlionrecords of the Santa Barbara earthquake of 13 Au gusl 1978. preliminary results $1.00

Minerals and rocks $1,00Geology of placer deposits $1.00Earthquakes: Be preparedl $0.35Basic Placer mining $0.35Fault hazard zones in California with supplements$1.00Meeting the earthquake challenge $2.50California jade $2.00Colemanite deposits near Kramer Junction. SanBernardino County. California $1.00State Policy lo r surlace mining and reclamationpraClice FREEEarthquake calalog o f CalifornIa. January " 190:>December 3t, 1974 $3.00

Trinity County. California. Mines and mineral ra sources 01 $3.50Monterey County. California. Minesand mineral resources of $5.00Shasta County. Cali forn ia. Mines and mineral resources of $7.50Imperial County. California. Mines and mineral resources of sa.50Alpine County. Cali forn ia. Mines and mineral resources of $3.50

Quicksifver $1.503 Chromlte $0607 lead and -zInc $1 25B Gold $1 50

ECONOMIC MINERAL MAPS - 1'1.000.000 plan,metric base.

_ _ CR 6_ _ CR 7_ _ CR 5_ _ CR '

___ SP 45_ _ SP49_ _ 5P 50

__ CR .

_ _ 5P 33_ _ 5P"_ _ SP 39___ SP 41_ _ SP42

___ The E lephan t as t hey saw it $2.00___ Fabncas $2.00___ B 190 TRIP G Mineralogy of the Laytonville Quarry. Men

docino County $0.50___ A walker's gUIde to San Francisco. Cal i fornia $0.50

_ _ SP 52_ _ SP 51

__ EM M__ EM M__ EM M__ EM M

__ PR 23__ PR 22

MAIL ORDER FORM

Manganese in California $2.00Pumice. pumicite. and volcanic Cinders in California $2.50Geo logy o f northern California $9.00Mineral resources of California $3.00The mineral economics o f t he carbona te rocks.l imestone and dolomite resources of California"00San Fernando. California. Earthquake 019 February1971 $13.00L,mestone, dolomite. and shell resources of theCoast Range Province. California $6.00Urban geology master p lan for Cal ifornia $2.508asic geology of the Santa Margarita area. SanLUIS Obispo County $7.50Geologyof the San Diego metropolitan area $12.00Geology of the Point Reyes pen insu la . MarinCounty. California $4.00

PRICE INCLUDES SALES TAX ON CALIFORNIA DELIVERIES

LoI I z~ BULLETINS

B 125 B 174

I ~ = = : : __ B ' ' ' 'I __ B '9 6I B 197I" B " Bg B '"mIQ B 200o __ B 202I :pansible shale resources of the Sen Jose-Gilroy

area. Santa Clara County. California $1.50SR 88 Geology 01 the Queen of Sheba lead mine. Death

10 Valley. 'nyo County. California $1.50SA 98 Natural slope stability as r el at ed t o geology. Sa nClemente area. Orange


21/23

MISCELLANEOUS MAPS

PRICE INCLUDES SA.lES TAX ON CALIfORNIA DELIVERIES

S- Tota l amount enclosed

BOUGUER GRAVITY ATLAS OF CALIfORNIA. Scale 1:250.CXXI

SEE BACK COVER

o FOlded $5.00o Rolled $6.50

Uncoloredo Rolled only. in a tube 55.50o Folded sa.OOColoredo ROlled $9.50

FOR CALIFORNIA GEOLOGY SUBSCRIPTIONS,

State Wide Coverage

GEOLOGIC DATA MAP SERIES. Scale 1:750.CXXI.

September 1979

STATE

NAME

CITYADDRESS

___ Map No.2. Geologic map of California t977

~ t~ "~ o___ Map No. I. Fau lt map of California with locations o f vOl-51canoes. the rmal spr ings . and thermal wel ls 1975 w~ o"~ ~ 81"~ ~ "~ ~ "~ X~ ~ >~ ~ u~ "~ - - - - - - - - - - - - - - - -e

COMPANY ~

z---------------- ~ ______________ -'-'UIP'--- ~


22/23

-DISTRICT OFFICES-

CALIFORNIA DIVISION OF MINESAND GEOLOGY DISTRICTS

- - - - - -T---- lS IS K rYOU

" r , I ,< I'.----L_

"


23/23

STATE OF CALIFORNIATHE RESOURCES AGENCYDEPARTMENT OF CONSERVATIONCALIFORNIA GEOLOGY

CALIFORNIA DIVISION OFMINES AND GEOLOGYP.O. BOX 29lIOSACRAMENTO. CALIFORNIA 95812USPS 350 840

SECOND CLASS POSTAGE PAlOAT SACRAMENTO, CALIFORNIA

ADDRESS CORRECTION REQUESTEDPLEASE E\IITER MY SUISCRIPTlO\ll TO CALIFORNIA GEOLOGY:10_

california geology magazine september 1979

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