california geology magazine february 1991

8/7/2019 California Geology Magazine February 1991

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A PUBLICATIONOF THEDEPARTMENT OF CONSERVATIONDIVISION OF MINES AND GEOLOGY

CALIFORNIAGEOLOGY

In This Issue IMONO LAKE EARTHQUAKE OF OCTOBER 23, 1990 2iDISPLACEMENT ALONG THE MANIX FAULT 33RECYCLING-EVERYONE'S CHAllENGE 39DMG RELEASES 40SP 103........ . 40SP 104 42BOOK REVIEWS 44

MAIL ORDER FORM . 45CALIFORNIA GEOLOGY SUBSCRIPTION FORM 46ANNOUNCEMENTS 48UNION PACIFIC RESOURCES FUNDS AWG SPEAKERS BUREAU .48USGS OPEN HOUSE AT MENLO PARK IN MAY 48

PETE WILSONGovernor

DOUGLAS P WHEELERSecretary lor R9SOtJfC8SEDWARD G. HEIOIG

o,r6C/Of'JAMES F DAVIS

StatB GeologtsrCALIFORNIA GEOlOGV slal1

/'fInIed DepaI'lmer11 01 GeneI. SeMcesOffice 01 Slat. P''''bnlI

Co"upond&"c& should b& .om&ssed 10 Ed,to,.CAlFORNlAGEOlOGY, 660 8&ra>l OriYe, s .a- . - . CAll6IIa-0131

Note to SubscribersCAUFORNIA GEOLOGY is approximately six weeks behind schedule. Manysubscribers. concerned by the lag in receivIng their monthly issues. wonder if theirsubscriptions have lapsed or have not beenrenewed. This is not the case. We aremaking every effort to meet production

deadlines and appreciate the understandingand patience of our subscribers . . . editor.

Cover; Oblique aenal view to the south of the south shore ofMono lake and the Mono Craters chain of volcanoes. PanumCrater, a nearly parleet pumice and ash (tephra) ring With acentral plug 01 obstdlan is the northernmost Mono Crater and isshown in the nght center. The Sierra Nevada is in the distance.The OCtober 23, 1990 earthquake occurred beneath the northshore of Mono lake. An article about this earthquake IS onpage 27. Photo by C. Dan Miller.

Don DuprasL&rla TabliloloUIse HuckabyJell Tambe"

SubIcnpDons $1000 pe l ~ Songle""",",' 51 2!i_Send . . . . . .. . . . , cha"O& at &dchss inIoI.....liOI\10CAlIFORNIAGEOlOGY.P 0 90 . 2980 .sac . - .CA958122980

Techmcal E d I ' o r ~Assis,anl EdItor'Graphics and Design:PublICations Supel'VlSOf;

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0Ms00n He3dQuiIrlets ' . '6 NiI1\h $l,'" 1)011s.cr_. CA i511.( T g ' & - " ~ ' 8 2 5 )l'I.obIic8tionIand lnIormalJoI'l 0lIicI660 8elCU1 Of . . . .S - _ . CA 9!>8,.-QI31Pubklnlatmauon 916-"S-5716lo s (; l l tD 107 South 8rGI


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Mono Lake Earthquake ofOctober 23, 1990

BySTEVE MeNUTI, Seismologist,

WILLIAM BRYANT, Geologist, andRICK WILSON, Engineering Geologist

Division of Mines and GeologyINTRODUCTION0 "October 23. 1990. a moderateearthquake of local magnitude (M L )

5.7 shook the Mono Lake area. a region known for j ls recent volcanic andtectonic activity. The earthquake(38"03'N: 1 1 9 ~ 0 8 ' W : depth 8 miles)was centered approximately 5 milesnorth 01 Lee Vining and 16 miles

To IIIIllgftpon

N

\

southeast of Bridgeport. near BlackPoint. an isolated fiat-lOpped hill on thenorth shore 01 Mono Lake (Hgure 1).Shaking from the earthquake was felt atapproximately Modified Mercalli Intensity VI in the local area and weaklythroughout much of northcentral Cali-fornia as far west as Sacramento and

MAIN SHOCK

Figure 2

the San Francisco Bay area. Damagewas light because the event occurred in asparsely populated region. However.landslides and rock falls caused by theearthquake blocked portions of Highwayt 20. east of Tioga Pass. closing it forabout one half day. Several smallerroads were closed for up to a week.

119 w

MONOLAKE

'"

E L - . 3 : : : J E = ' = = = ' ~ E = 3 = = i ' ' = = : E = = l '....Figure 1. Map show.ng the OCtober 23.1990 ma.nshock (star) and aftershock (round dots) locations With respect to the Mono Lake faultand Mono Lake. A small fault mapped by LaJOie (1968) is located Just east of the ma.nshock. EpiCenter data counesy of the U. S. Geo-Ioglca/SutVey. Mono Lake fault generalIzed tram Bryant (1984).

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TABLE 1. DATA RECOVERED AT CSMIP STAl iONS FROM THE OCTOBER 23, 1990 EARTHQUAKE NEAR MONO LAKE.The fraction at lhe acceleration at gravity recorded is g. tor verllcal motion v. and horizontal motion H.

Epicentral MaximumStation Structure Station Distance Acceleration SiteNo. Name Type Coordinates Ikm) Ground Structure Geology55031 Tioga Pass small 37.940 N 12 0.04g H gramte

shelter 119.190W 0.04g V65500 Bridgeport small 38.2.55 N 26 0.07g H alluviumshelter 119.220W 0.02g V55429 June lake 2-story 37.783 N 29 0.02g H granitebUilding 119.075W 0.03g V54301 Mammoth lakes- 1-story 37.641 N 46 O.04g H 0.08g H glacial

l-story school gym building 118.963 W 0.02g V depositsSource: California Strong Motion Instrumentation Program (CSMtP)

This article summarizes the seismological features of the earthquake andrelates the findings made during a surface fault rupture investigation of theeplcentral area by Division of Mines andGeology (DMG) geologists. To demonstrate how this earthquake fits into theregional tectonic selting. the characterof this event is compared to that ofother noteworthy seismic events thathave occurred over the last 12 years.

SEtSMICITYThe earthquake occurred at 11: ISp.m. Pacific Standard Time (PSTI onOctober 23. 1990 at a depth of 8 miles

below the Earth's surface. The locationof the mainsl lock and the first few daysof aftershocks are shown in rtgure 1.The aftershock sequence was fairlyweak. and included only three eventswithin 2 magnitude units of the mainshock during the following month (2magnitude units is a commonly usedway to compare events of unequal size).The largest aftershock was a magnitude4,I event that occurred on November 5at 12:16 PST just southwest of themainshock. The aftershocks define a5-mile-long trend roughly north-northwest to south-southeast. approximatelyparallel to the east-dipping Sierra Nevada frontal fault. which is called theMono lake fault in this area (Rgure I).Fault orientation and direction of slipmovement (focal mechanism) was determined for a smaller foreshock that

occurred several seconds before themainshock. This mechanism showedpredominantly right lateral strike'slip motion. with the inferred fault surface (faultplane) aligned along the same trend asthe aftershock zone ry..;. Peppin, University of Nevada at Reno. personal communication), The subsurface fault planewas found to be nearly vertical. dippingsteeply to the southwest. Although thisdip is towards the Sierra Nevada front. itis stili probable that the earthquake occurred on the Mono Lake faull; the 8mile depth of the event and its locationeast of the surface trace agree with thehigh-angle, easterly dip of the faulLThe preliminary local magnitude ofthe earthquake is MIS.7 based on meas

urements made by University of California. Berkeley. The preliminary bodywave magnitude provided by the National Earthquake Infonnalion Center(NElOts M b 5.2. and the preliminarysurface wave magnitude is M 5.1Four stations of the California Strong

Motion Instrumentation Program(CSM1Pl recorded the main shock(Table I). Peak ground motions rangedfrom 0.02 gravity (g) to 0.07 g atground sites. and 0,08 g at the rooflevel of a gymnasium in the town ofMammoth lakes. The four triggeredstations ranged in epicentral distancefrom 7 to 29 miles. Seven other localstations at distances greater than 29miles were operational but did nottrigger (CSMIP staff. 1990).

FIELD OBSERVATIONSThe Mono lake area was visited by

DMG staff on October 24 and 25. thetwo days following the ML 5.7 earthquake. The scope of the field studyperformed by DMG was two-fold: (1) toInspect the trace of the Mono lake falilt[zoned for Special Studies in 1984 under the Alquist-Priolo Act (Hart, 1990)Jfor evidence of surface rupture associated with this earthquake. and (2) to ex-amine the area in the immediate vicinityof the epicenter for surface effectscaused by the earthquake, A smal1fauhnorthwest of Black Point was inspectedfor fault-rupture by U. S. GeologicalSUIVY geologists.The Mono lake fault is an approxi

mately II-mile-long, east-dipping normal fault that offsets late Tioga glacialoutwash deposits and is considered tohave ben active during the Holocene(Bryant. 1984). Traces of the Monolake fault were inspected at three locations: (I ) the paved Lundy CanyonRoad along the northcentral part of thefault zone. (2) the paved road just northof Lee Vining Creek. and (3) the intersection of the southern Mono lake faultand Highway 120 (Figure O. Evidenceof primary surface fault rupture was notobsetved along the Mono Lake faultzone, Pre-existing extension cracks inthe pavement of Highway 120, whichwere generally aligned with the trace ofthe south Mono Lake fault. had freshappearing hairline cracks. However,

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TABLE 2. SUMMARY OF FIELD OBSERVATIONS (Reier to Figure 2 for locations).

Localily Description (Photos)Possible shaking cracks along southern flank of Black Point. Cracksare somewhat sinuous and generally parallel the slope. Most of thesefeatures consist of small, coalescing collapse pits about 2 inches indiameter on slightly mounded sand.

2 P r e ~ e x i s t i n g f issures in bedrock trend about N30"E. Many of thesefissures have fresh cracks in the eolian fissure-fil l. The cracks occuralong the sides of the fissure at the fissure-fill/bedrock contact(Photo 2). These cracks have vertical displacements of up to 5 inches(Photo 1), locally form graben (Photo 2). and often are associated withcollapse pits (Photo 3).3 Large collapse pit is about 4 feet in diameter and 5 feet deep (Photo

4). However, the pit is located within a l inear trough which may be asouthwest extension of the fissures developed in the well-induratedvolcanic deposits.

Photo 1. Crack in eolian sand paralleling pre-existing bedrock fracture. This crack formedone side of a small graben. Photos by R. Wilson.

these fresh cracks are most likely related to shaking rather than surfacefault rupture because the cracks had nomeasurable vertical displacement. didnot extend into the road shoulders. andwere not observed along a well-definedscarp to the north and south.Anticipating that bedrock areas in

the vicinity of the earthquake epicentermay have been affected. DMG geologists inspected Black Point to ascertainthe degree of shaking near the epicenter. Table 2 is a summary of the observations made at Black Point. BlackPoint is an exposed remnant of a MonoLake guyOt (Christianson and Gilbert.1964). (A guyot is a flat-topped volcano that erupts under water: wave action is responsible for making the topflal.) Black Point contains sets of vertical fissures. 2- to 3-feet wide and 30- to50-feet deep. trending predominantlyN30cE through basaltic cinder andaltered basaltic cinder capping the hill(Lajoie. 1968). Recent cracks (PhotoI). graben (Photos 2 and 3). and collapse pits (Photos 2. 3. and 4) were observed in loose eolian sands that infillthe pre-existing bedrock fissures(Figure 2: Table 2).

Although the soft-sediment featureswere large enough to be quite noticeable. there was no evidence of recentfractures or cracks that propagated intothe bedrock outcrops. Because the

cracks. graben. and collapse pits werefound only in the loose fissure-fillingsand. they were probably secondaryseismic. or groundshaking. effectswhere bridged sediment within the fissures collapsed. Other small sinuouscracks contained what appeared to besmall cone-shaped collapse pits. Thesecracks were observed in the loose sandaway from the bedrock outcrop areasand appeared to be parallel to outcropscarps (Figure 2: Table 2). These sinuous cracks were probably caused by

groundshaking and. in turn. producedlateral spreading and settlement of theloose sandy sediments.A small fault. mapped by Lajoie(1968) and located directly above the

mainshock epicenter northwest of BlackPoint. was inspected by Malcolm Clarkof the USGS for surface rupture. Nosurface rupture was observed along the}-1/2 mile length of the fault (MalcolmClark. personal communication).

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Photo 3. Downdropped block 01loosely consolidated. eolian fissure-flit.The nature of the fissuretill depoSitwas illustrated when one 0' the authors stepped across the crack 'romleft of the picture. only to have the fillcollapse beneath hiS footln(jlcated bythe hole. The newly 'ormed collapsePit was about 10 inches In diameterand 3 'eet deep

Photo 4 Large col lapse Pit IS about4 feet In dIameter and Sleet deepHowever. the Pit IS located Within a hneartrough whICh may be a southwest e:ttension ot the fissures developed in the weltIndurated volcamc depoSits.

Photo 2. Pre-exiSting 'Issures In bedrock 'rend about NJO E.Many 01 these fissures have fresh cracks In the eolian fissure-Jill.The cracks occur along the sides of the fissure at the fissure-filiibedrock contact. These cracks have vertical displacements 0' upto 5 inches. locally 'orm graben. and often are associated With collapse pits shown In Photo 3.

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(4) The seismograms appear to betypical of tectonic events, based onscanning the available data, There isno suggestion of enriched low frequencies or any volcanic tremor-like signals.

(3) The Mono Lake event has theclosest relationship to the Sierra Ne-vada frontal fault system of any of theprincipal events based on the location.mechanism. and fault geometry,

(2) The event occurred in a particulararea that had virtually no previously recorded earthquakes within 6 miles.Most volcanic areas. on the other hand.have high background seismicity rates.

(1) The event had the smallest number of aftershocks of any of the principal events shown in Table 3. It is definitely not swarm-like, as are manyother earthquake sequences that occurin volcanic areas,

The authors interpret the MonoLake event to be primarily tectonic andnot magmatic in nature, based on fourfeatures:

Based on these observations. the authors conclude that the Mono Lakeearthquake was tectonic and that theMono Lake fault was the probablesource. The possibility exists that theearthquake's source could have beenthe small fault northwest of BlackPoint. However. due to the relativelylarge size of the earthquake and the dis-tribution of the aftershocks, the onlyfault large enough to be the likelysource of the event is the Mono Lakefaull. The greater than usual focaldepth of the earthquake may accountfor the absence of surface rupture onthe Mono Lake fault. The earthquake'soccurrence demonstrates that theMono Lake fault is active. and suggeststhat adjacent sections of the fault arecapable of producing moderate-sizedevents. The Mono Craters-Long Valleyregoo thus continues to be tectonicallyactive. and will remain an area of intenSTve interest arx:l study.

{

I l.fJ.rt t ...,I

MONO LAKE

Long Valley caldera between 1980and 1984, (2) uplift centered on theresurgent dome of the caldera. and (3)evidence of increased lumarolic activity--suggested that possible magmaticintrusion was occurring (Hill and others.1985). Because of the recent seismicand possible magmatic activity in theregion. the question arises whether theMono Lake earthquake was related tovolcanic processes because of its doseproximIty to the Mono Craters, whichlast erupted about 600 years ago (Siehand Bursick. 1986),

~ b " ' = " ' 5 " , , " ~ : " = _ " ' 5 " " " " " - " ."SCAlE 1 24000

Over the last 12 years the MonoCraters-Long Valley area of easternCalifornia has been one of the mostseismically active regions in the state.Thirty-four earthquakes with ML 5.0have occurred in the region bounded byIatiludes 37 25' N to 38 10' and longitudes 118 OS' W to 119 07' W (Savage and Cockerham, 1987). Most ofthe larger earthquakes have occurred inseven distinct episodes: the Mono Lakeshock is the Ialest ITable 3). Theseeanhquakes-along with (l ) repeatedswarm events in the south moat of

Figure 2. Detailed map of Black Point. showing locations 01 observations as described inPhotos 14 and Table 2. P r e e ~ i s \ l n g fissures In hydrothermally altered basaltic Cindershown as thin line With predommanlly N30 E trend. Base map adapted from the U. S.Geological Survey Negillsland 7.Sminute quadrangle. scale 1:24,000.

DISCUSSION

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TABLE 3. PRINCIPAL EARTHQUAKE EPISODES IN THE MONO CRATERS-LONGVAl lEY AREA (1978-1990).

Date Name M' Number of Rererence,(mo,datyr) aflershocks1

10/04f78 B ishop ear thquake 5.8 10 Ryall and Rya ll (1981)05'24-27-80 Mammoth lakes 6.1.6.0. 29 Uhrhammer and

earthquakes 6.1. 6.2 Ferguson (1980)09130'81 Laurel Mountam 5.9 6 Person (1982)

earthquake301;07183 Sooth Moat 5.4.54 17 Savage and

swarm Cockerham (1984)11123-26184 Round Valley 6.1 4 SmJth and others

earthquake (1988)07120-31/86 Chalfant Valley 5.9.65. 20' Cockerham and

earthquake 5,7.5,6.5,8 eo","" (1987)10123'90 Mono lake 5.7 2 NEIC (1990)

earthquake, Local magl'lltudes from U,C, Bel1lekty as publIshed In monthly Preimlnary

DeterrrunatlOn of EPfCenters bulktllns oflhe NatlOOal EarthquakeInformatIOn Center

1 Number of ahersl'locks Wlthln two magnitude Ul'llts of malnshoc:k wlthm twodays, Data from monthly P r e ~ m l n a r y DeterminatIOn of EPICenters

) ThIs event has not been assigned a formal name In the Ilterature Someworkers In the field althe lIme. however. re'erred 10 II as the laurelMounta,n earthquake

ThIS value Includes aherShocks 01 the M 59 !oreshock 01 07/20186

REFERENCESBryanl, W.A.. 1984. EVIdence of recentfaulting along the Mono lake fault zone.Mono County. Call 'ornia: California Divislon 01 Mines and Geology OpenFileReport 84-55 SAC. scale 1:48,000Cockerham. R 8" and Corbell . E. J..1987. The July \986 Chalfant Valley.Callfornla, earthquake sequence: prel,mlOary S91smologlcal results 'o r thema(Of events and aflershocks: Bullelln

01 the seIsmological SocIety of AmerICa.v 77. p 280-289ChnSbanson. M N , and Gilbert . C M .1964. BasahlC cone suggests coo

structlOnal ongln of some guyots: Scie ~ v, 143. P 240242,CSMIP Statl. 1990. Summary of CSMIPstrong-motIOn records for the OCtober23. 1990 earthquake near Mono Lake.CaMOITIIa CabfOfOla 0Msi0n of 'o,,"esand Geology Strong MelJOn lnstrumen

lalJOn Program. Saaamenlo. Cahfomla., pHar1. E.W. 1990. Fault ruplure hazardzones In Cal.torl'll8; revtHCl 1990 OM

SIOn oj M,nes and Geology SpeoaJ Pub-licatIOn 42. 26 P

Hill. D. P" Bailey. R. A. and Ryall. AS .1985. ActIVe tectonIC and magmatICprocesses benealh long Valley caldera.eastern CalifornIa; An overview Journal01 GeophYSICal Research. v, 90, P"1111'120.

Lalole. K. R., 1968. lale Ouaternary stratigraphy and geologIC history of Mono Basm. eastern California Ph.D theSIS, U,...-verSlty of Caillorma, Bel1letey, 270 pNEIC (NatIOnal Earthquake InformatIOnCenter). 1990. Prellmmary Determlna

tIOn 0' Epicenters (weekly). No 4390,U, S GeologICal Survey. 2 pPerson, W J , 1982. S9lSmologlCal notes Seplember-Oclober 198\ Bullelln of 1I'IE1S9lSmologlcal SocIety 01 AmerICa. v, 72,P '451,Ryall, A_. and Ryall. F .. 1981. SpallaHemporal vanallOtlS In selsmlClty precedIngthe May 1980. Mammolh Lakes. Calilor

013. earthquakes: Boletm of the S9lsmoIoglCal Sooety of AmerICa. v 71. P747-760

Savage. J. C" and Cockerham. R. S..1984. Earthquake swarm 10 long Valleycaldera. Callfornia, January t983: evidence lo r dike inflation: Journal 01 GeophySIcal Research, v. 89. p. 83158324.savage. J. C .. and Cockerham. R. S..1987. OuaslpenodlC occurrence ofearthquakes In the 1978-1986 BlshopMammolh Lakes sequence. easternCaliforl'Ha: Bulletin 01 the SeismologicalSoclOty of Ameoca. v. n. n. 4.P 1347-1358.S1eh. K. E .. and Bursik. M I., 1986. Meslrecent eruption 01 the Mono Craters.

eastern cenual Califorma Journal ofGeophYSICal Research. v 91.P 12539-12571.Struth. K.D Priestly. K_F. and Cockerham.R,S,. 1988. The 1984 Round VaDey.Calrtorl'lla. earthquake sequence Ge0phYSICal Journal, v 95. p. 215--235Uhrhammet. R. A_. and Ferguson. R W1980. The 1980 M3fTWn01h Lakes earthquake sequence. Cal.tOfl"ll3 0MsI0n ofMInes and Geology Speaal Report ISO.P 131-136.

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Displacemen the Manix Fault

. ...Photo 1. Aerial view of the M a n i ~ faull zone looking east The main branch of the Manlx fault passes up the l inear val ley in the right fore-ground. The Cady Mountains are on the nghl and Alton Canyon IS the rugged area just below the horizon. The dissected mountam Inthe left foreground is lhe western granitic fanglomerate deposit lhat has been otfset approximately 3 miles from its counterpan In theAlton Canyon area. PhD/OS by N. Meek.

The Mojave block IS a CenozOIC age lea-ture thai Is presumed to have originated bymovement relaled to lhe San Andreas andGarlock laull systems. Most or the rockunitS in lhls region underlie a veneer 01Ouaternary allUVium and range in age IromPrecambnan to Miocene. The complexstructural geology of thiS region has beennotoriously dilticull to comprehend. In re-cent years, however, the regional lault pat-lern in the Mojave block has become bellerunderstood. This article describes the dis-placement ot one MOjave block taul!. theManlx lault. Bolded terms within the textare placed In a glossary attha end 01 theartlCle...OOllor

INTRODUCTIONT he Manix fault is a major east-northeast trending fault in the centralMojave Desert (Figure 1. Photo 1). Vis-ible faulting and geophysical data indi-

cate that the Manix fault may be about24 miles long (Hamilton. 1976). TheCady Mountains are to the south of thefault and Alton basin is to the north ofthe fault. Where it is exposed. the Ma-nix fault cuts Pleistocene lake beds andforms prominent scarps (Keaton andKeaton. 1977). Both ends of the faultzone are obscured beneath thick upperPleistocene and Holocene alluvium.Tectonic models of the Mojave Desert lead investigators to suspect that theManix fault is a left-lateral strike-slip

fault' (Garfunkel. 1974: Carter andothers. 1987), Some studies have accepted this assumption (such as Dokkaand Travis. 1989; 1990), although fieldevidence of significantlelt'lateral displacement has not been documented.

In 1947 a magnitude 6.2 earthquakeoccurred on or near the Manix fault withan epicenter near Buwalda Ridge (Richter and Nordquist. 1951: Richter, 1958).Field investigations of the surface ruptureindicated left-lateral offset of 2 to 3inches on the Manix fault However. theaftershock sequence suggested right-lateral strike-slip motion on a plane perpendicular to the Manix fault,Recently. McGill and others (1988)mapped the Manix fault lone west ofBuwalda Ridge and found field evidencethat the fault has been active throughoutthe Quaternary. However. neither theamount of lateral offset or the directionof movement could be determined.

'Balded terms are In Glossary on page 37,

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Additional field and laboratory datasuggest that the granitic fanglomerate tothe north of the Manix fault and thegranitic fanglomerate to the south of theManix fault are parts of the same deposit. This hypothesis is derived fromthe following evidence. (1) The graniticfanglomerate is over 300 feet thicknorth and south of the Manix faull. (2)Analogous sedimentary features exist inboth areas: a distinctive sequence of alternating boulder and pebbly beddingoccurs at both sites (Photos 2 and 3).Moreover. thick paleosol development.or other evidence of basin stability during deposition of the granitic fanglomerate, is absent in both deposits. (3) Comparative clast lithologies. sizes. and extent of rounding is similar at both sites.

To determine whether the twogranitic fanglomerate deposits wereonce a single deposit. several representative cobbles and mineralogically distinctive clasts were collected from various outcrops of the granitic fanglomerate north and south of the Manix fault.Thin sections of clasts from both groupswere prepared and petrographically analyzed ITable 1). These analyses indicatethat lithologically identical clasts in thetwo deposits originated from the samebedrock source areas.

",,"-,/,,",,,,

",,," ,, ', ,0 M; 50Lateral Displacement

The granitic fanglomerate can onlybe found in the eastern half of the CadyMountains and appears to have oncefilled a broad northwest-trendingtrough. It has been faulted into blockssince its formation (Figure 2). South ofthe Manix fault the granltlc fanglomerate is bounded on the west by a normalfault and is exposed along a 1.3- to 2mile-long segment of the Manix faultwithin Afton Canyon (Photo 2). Northof the Manix fault the granitic fanglomerate is exposed along a 1.3-to 1.7mile-long segment as a highly dissectedmountain (Photos I and 3). Left-lateralmovement on the Manix fault appearsto have displaced the granitic fanglomerate by about 3 miles to its present lo-cation. Fault of/set is only approximatebecause: (I ) the deposit margins are either buried or faulted, and (2) no piercing points-or sites that can be used todetermine the exact component of faultoffset-have been discovered in thegranitic fanglomerate.

Most of the northern Cady Mountains is composed of dark Miocene vol-canic rocks (Danehy and Collier. 1958:Dibblee and Bassett. 1966: Moseley.1978). However. along the northeastern edge of the Cady Mountains thereis a light-colored boulder fanglomerat e that is more than 300 feet thick.The fanglomerate is composed of a di-verse mixture of granitic and volcanicclasts which cannot be traced to nearbybedrock outcrops in the northern CadyMountains. Because of the contrast be-tween the numerous granite boulders inthe fanglomerate and the adjacent vol-canic bedrock, the thick fanglomeratedeposit has been informally termed the"granitic fanglomerate" in this article.

Figure 1. Fault map 01 southern CahlormashowlI'Ig the location of the Mamx fault (faultmap aftor Luyendyk and others. 1980),

The following evidence shows thatthe total displacement along the Manixfault is approximately 3 miles in a left-lateral sense.

' :'4'" _....... ;r,.'

DISPLACEMENT OF THEGRANITIC FANGLOMERATE

: '. " : ~ - - - - -,' , :" .'::)10

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o,Mi le s

Photo 2 locat ion

MANI)(

2

Photo 1locat ion

IFigure 2. Map at the eastern Manix fault zone. The shaded areas are outcrops of the granitic fanglomerate. The granitic fanglomeratehas been ollset in a left-lateral sense approximately 3 miles by the main branch of the Manix fault. The terrain is very rugged and manyof the faults disappear beneath the alluvial cover. Geology and faults after Danehy and Collier. (1958). and Moseley (1978).

Photo 2. Panoramic view of the eastern granitic fanglomerate deposit in Afton Canyon(see Figure 2 for location).

(4) Due to distinctive bedding, the dissection and weathering of the graniticfanglomerate on both sides of the Ma-nix fault have produced remarkablysimilar erosional landscapes (Photos 2and 3).Vertical Displacement

Recent investigations indicate thatsignificant vertical offset may also haveoccurred along the Manix fault (Keatonand Keaton. 1977: McGill and others.1988). Investigations west of BuwaldaRidge indicate that sediments in Aftonbasin adjacent to the Manix fault havebeen repeatedly warped during theQuaternary and that wrench-typefolding. found adjacent to the fault.may indicate strike-slip movementcaused by the fault (McGill and others.1988).

Substantial vertical offset occurredalong the Manix fault during the midand late Pleistocene and rapidly raisedthe Cady Mountains south of the fault(Meek. 1989b). Elevation measurements taken on a series of ancestralLake Manix beach ridge crests atop thewest edge of Buwalda Ridge indicatethat at least 6 feet of vertical uplift mayhave occurred between 27.000 yearsago and 17.000 years ago. However.

the lower beach. about 14.000 yearsold. occurs at the same elevation asother beaches in the basin of equivalentage. These measurements suggest thatlocal uplift might have occurred periodically in intervals that were greater than14.000 years.

The vertical displacement associatedwith the Manix fault zone appears to becaused by increasing north-south compression since the middle Pleistocene.Additional evidence of regional northsouth compression throughout the central Mojave Desert has been presentedby Bartley and others (1990).

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Photo 3. Close-up view 01 the western granltlC fanglomeratedePOSit (see Figure 2 for location).

Afton basin is adjacent to the Manix fault and contains anextensive and mostly continuous record of late Tertiary andQuaternary sedimentation. On the basis of tephrochronol-ogy. paleomagnetism. an d extrapolated deposition rates.(Jefferson, 1985; R Adams. written communM::ation. 1989).portoos of Afton basin near the Manix fault appear 10 havedeveloped during the late Pliocene as a transtensionalbasin associated with Ieftlateral movemenl on a curvedsegment of the Manix fault.

IMPLICATIONSSignificant left-lateral displacement on the east-northeast

striking Manix fault in t he northeast comer of the Mojaveblock broadly supports previous model predictions by Garfunkel (1974) and Carter and others (1987). Moreover, measurements of Ihe amount of lateral offset will facilitate reconstruction of the Miocene paleogeography.If left-lateral movement is presently continuing. i t may be

responsible for the eastward offset of a possible relict outletchannel of Lake Manix (Photo 4). Lake Manix was a 200square-mile Pleistocene freshwater lake lhat repeatedly inundated some local basins due to increased runoff from the SanBernardino Mountains and reduced evaporation during thePleistocene. For most of its history, Lake Manix was the terminus of the M ~ v e River and did not overflow the Manixbasin rim. However. during Illinoian time (about 400.000years ago) i t may have spilled over the rim near Afton Can-yon, carving a broad outlet channel. 10e truncated outletchannel, originally described by Weldon (19821, now lies sev-eral hundred feet east of the probable lake edge. and morethan 15 feet above lhe highest Iale Pleistocene lake stage(see Meek. 1990. for analyses of the rel ict channel and lakestages).

TIMING OF LATERAL DISPLACEMENTAlthough the granitic fanglomerafehas not been radiometrically dated,

stratigraphic relationships indicate that;t ;s younger than the early Miocenevolcanic bedrock that lies adjacent to itin the northern Cady Mountains (Moseley, 1978; Miller. 1980). Consequently.lhe granitic fanglomerate is either lateTertiary age (Dibblee and Basseu.1966; Moseley. 1978) or Plio-Pleistocene age (Danehy and Collier. 1958).lnerefore, lateral displacement on theManix fault is middle Miocene oryounger Sedimentary evidence sug-gests that much of the lateral movement on the fault occurred more than 2million years ago and couki be contem-poraneous with regional late Cenozoicmovement on northwest-striking faults(Dokka. 1983).

TABLE I. PETROGRAPHIC DESCRIPTION OF THIN SECTIONS FOR FIVEDISTINCTIVE SAMPLE CLASTS IN THE GRANITIC FANGLOMERATE.

Sample Clasl Description

Intrusive A HornblendecllnopyroxeneblOllte dlonte WIth large poikJlltlC amphiboleencloSing biotite, plagIOClase. c l l n o p y r o ~ e n e . and opaque mineralsHornblende IS altered In part to tMotJte and/or chlonte.IntruSIVe B Coarse-rramed biotite granite wllh large sphene crystals. The potasSIUm feldspar is perthltJc mlCl"octine. BlOllle has altered to chIontealong cleavageextruSIVe A Orange-brown colored welded rhyolite tuff WIth sarudine and plagIO-clase phenoaysts. lithic fragments. biotite and amphibole aremoorconstJluents Coolams distmctlVe amphiboleoch cumulate mduSlOns.E ~ l J u s t v e B Grey-purple colored fine-gralned rhyolite With strongly zoned plagIO-clase Contall1S fare dinopyroxene, onhopyroltene. and biotrle whichare nmmed by opaque minerals.Extrusive C Porphyritic dant grey andeSlte(?llhal e ~ h l b l t s Intense but vanablehematitic alteration. Contains c l i n o p y r o ~ e n e . orthopyroxene, and farehornblende and biotite. Malic minerals are usually rimmed by opaqueminerals.

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Photo 4. Aenal view of Ahon Canyon IooIung east. The relict channel can be seen In thelower foreground. The Mafllx fauh passes northeast through Ahon Canyon In the lower leftcomer of the photo

fanglomerate: 5edlmenlary rock UOll usually consisting 01 waterwom clasts Ihat weredePOSIted In a n a llU Via l fan and later cementedlake sfand: Water level of an ancestral lake thaI remained stable for an edended pe-riod of l ime.leftlateral slrike-sUp fault: Component of movement along the strike of a fauh andon which displacement appears to the left of lhe side opposite the viewer,paleosol: A burted anoent SOIl honzon: some paleosols are miDlons 01 years oldtephrochronology: Descnblng and dat10g tephra (claslJc rock matenal ef8Cled from avoIcarnc venl).transtensional basin: A baSIn formed by stnke-slip fault motIOn and is accompamedby a component 01 extensIOn that IS crOSSWIse (or transverse) to lhe fauh.wrenchtype fold: Delormatlon caused by strike-slip stress acoompan,ed by a component of transverse comprltSSlOn.

Glossary

Danehy, EA, and Collier. J.T.. 1958. ArealeconomIC geology map ot T. 11 N. R.5 & 6 E: Southern PaCific MineraiSurvey, 1:24,000.Dlbblee, T.W Jr .. and Basse". A.M .. 1966.GeologiC map of the Cady Mountainsquadrangle, San BernardIno County,California: U.S. Geological Survey, Map

1467. 1:62.500.Ookka. R K. 1983. Displacements 00 latecenoZOIC stnke-sllp fauJls 01 the centralMOJ3ve Desert. CalifornIa: Geology. v11. P 305308.Doklc.a. R.K, and TraVIS. C.J .. 1989. Timespace pa"erns of late cenoZOIC stnkeslip faufbng In the Mo)3ve Desert. cali-fornia In Reynolds, R.E., editor, Thewest-eenlfal MO)3ve Desert: Ouaternarystudies between Kramer and Ahoo Canyon: san Bernardino County MuseumSpecIal Publicaoon, p 65-68Dokka, RK, and TraVIS. C.J .. 1990. LateCenozOIC strike-slip fauillng In theMO}3ve Desert. Califorrna: TectonICS. v9. p 311-340.Garlunket. Z., 1974. Model lo r the late ce-noZOIC tectonIC hIstory of the Mo,aveDesert. California, and for its relalloo toadJacenl regions: GeologICal Soclety 01Amenca Bulletin, v. 85. p. 1931-1944Hamilton, P., 1976. A geophySICal study ofthe Manix fauh: Its tectonIC relatlonsrupto the western MOjave Desen, San BernardinO County. California: UnpublishedM.S. theSIS. CaJilornia State UniverSity.Los Angeles, 101 p.Jefferson. G.T.. 1985. Stratigraphy andgeologiC history of the Pleistocene Ma

ni . FormaMn, central Mojave DesertCalifomla in Reynolds. R.E .. compiler.GeologiC investigations along Interstate15, Cajon Pass 10 M a n i ~ Lake, California: San Bernardino County MuseumSpeCial Publication, p. 157169.

REFERENCESBartley. J.M., Glazner, AF .. and Schermer,

E.A, 1990, North-south contraction 01the Mojave block and strike-slip tectonICS In southern CaliforOla: SCIence, v248, p. 1398-1401.

Carter. J.N.. Luyendyk. B.P.. and Terres.R.R" 1987. Neogene clockWise tectoniCrotation of lhe eastern TransverseRanges, California. suggested by paleomagnetic vectors: Geological Society ofAmerica Bulletin, v. 98, p. 199-206.

ACKNOWLEDGMENTS

Tectonic activity on the fault may beresponsible for the sudden release ofwater from Lake Manix during the Pleistocene. which resulted in carving AftonCanyon (Meek. 1989a). Because thewestern end of Afton Canyon begins althe intersection of the Manix fault andthe edge of the ancestral Lake Manix(Weldon. 1982). it is possible thatmovement on the fault during the maximum late Pleistocene lake stand mayhave led to the rapid draining of LakeManix and the formation of AftonCanyon.

Although the late Pleistocene lakesdid not drain via the channel (Meek.1989b: 1990). earlier lakes in the basinmay have. Significant lateral and vertical movements along the Manix faulthelp to explain the present localion andelevation of the relict channel.

We thank Ron Dorn. Arizona StaleUniversity. Tempe. AZ. for the use ofunpublished cation-ratio dates: Ray In-gersoll. University of California. LosAngeles; Sally McGill. California Institute of Technok>gy. Pasadena; andGeorge Jefferson. George C. PageMuseum. Los Angeles.

CAUfORNtA GEOlOGY FEBRUARY 1991 J7


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Keaton. J.A.. and Keaton, R.T., 1977, Manix fault zone. San Bernardino County,California: CALIFOANIA GEOLOGY, v.30, p. 177-186.Luyendyk. B.P" Kamer!ing, M.J" and Terres, A" 1980, Geometric model forNeogene crusta! rotations in southernCalifornia: Geological Society of America Bulletin, v. 91, p. 211-217.McGill, S.F.. Murray, B.C .. Maher, K.A ..Lieske, J.H. Jr., Aowan, L.A" andBudinger, F" 1988, Quaternary historyof the Manix fault. Lake Manix basin,Mojave Desert, California: San Bernardino County Museum Association Quarterly, v. 35, p. 3-19.

Meek. N" 1989a, Geomorphic and hydrologic implications of the rapid incision ofAfton Canyon, Mojave Desert, California: Geology. v. 17, p. 7-10.

Meek, N" 1989b, Physiographic history ofthe Afton basin. revisited In Aeynolds,R.E., editor, The west-central MOjaveDesert: Quaternary studies betweenKramer and Ahon Canyon: San Bernardino County Museum Special Publication, p, 78-83.Meek, N" 1990. Late Quaternary geochronology and geomorphology of the Manixbasin, San Bernardino County, California: Unpublished Ph.D. dissertation,University of California, Los Angeles,212 p.

Miller, S.T., 1980, Geology and mammalianbiostratigraphy of a part 01 the northernCady Mountains. Mojave Desert, California: U.S. Geological Survey, Open-FileAeport 80-878.

Moseley, C.G., 1978, The geology of aporlion of the northern Cady Mountains, Mojave Desert. California: Unpublished M.S. thesis, University ofCalifornia, Aiverside, 131 p.Aichter, C.F .. 1958, Elementary seismology: W.H, Freeman & Company. SanFrancisco, CA, p, 516-518,Aichter, C.F., and Nordquist. J.M.. 1951,Instrumental study of the Manix earthquakes: Bulletin of the SeismologicalSocielY 01 Amenca, v. 41, p. 347-388.Weldon, R.J, II, 1982, Pleistocene drainage and displaced shorelines aroundManix Lake In Cooper, J.D., compiler,Geologic excurSions in the Californiadesert: Geological Society of America,Cordilleran section held trip guidebook,p. 77-81. .....

Chaos Crags and Chaos Jumbles at the base, Lassen National Park. Lassen County. The Crags formed about 1,000 to 1.200 yearsago and are massive dacite plugs that had erupted into older volcanic craters. Violent volcanic explosive eruptions 01 incandescentavalanches preceded the formation of the viscous dacite plu9s at the Cra9s. Large quantities of steam were reported (Ising Irom theCrags from 1854,1857, suggesting that the volcanic life of the Crags extended over 1,000 years. They may not yet be exllnc!. TheJumbles are a chaotic avalanche deposit formed about 300 years ago. This deposit is 2.5 miles long and covers about 4.5 squaremiles. Photo by Sylvia Bender-Lamb:"

38 CALIFORNIA GEOLOGY FEBRUARY 1991


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A Page for Teachers RECYCLINGEveryone's Challenge

The litter pick-up walk and recycling drive are two ",'aYS toinvolve your students in the recycling challenge-one of themost important challenges in their lives. It is imperative thatrecycling be done. If children learn to be kind to the Earth.the Earth will reward them by being the kind of place Itshould be - clean and livable. If children are taught to recyclewhen they are young. it will become second nature. They willmeet the challenge and everyone will benefit from it.These activities can involve your class alone or all theclasses in the school. [t would be more effective (and morefun) if the entire school were involved. Maybe a friendly competition among the classes would help moliviate students andteachers alike.

Nonproht groups collect recyclablematenals at drop-ott locations.

Organize a litter pick-up walkto c lean up the area.Tell the students that it may take hundreds of years foran aluminum can to decompose. You can also talk aboutthe problems associated with burying trash in landfills. Ex-plain that toxic runoff (rom landfills is often a very seriousproblem. Also. many areas are running out of places to puttheir trash. As an added incentive. you can begin yourrecycling drive (see below) with the pounds and pounds ofglass. aluminum. and plastic you collect during this walk.

Plastics can be recycled too. Because plastic is made frompetroleum. a valuable mineral resource. its conselVation isespecially important. Plastics are also a big part of the problem of overflowing landfills. Most plastics are not bicxlegradable (they do not decompose by natural processes).Organize a recycling drive.

1 . Decide what you want to recycle. You can collectnewspapers. glass. plastlc. and/or aluminum Also. decide ona time frame for the drive. Will it last for one day or for several months?2. Contact a recycling collector several weeks before thedrive is held. Check on the recycling guidelines. For example. most glass and can collectors want clean containers.

Also. many glass collectors require that you remove metalcaps and rings and separate the glass by color.3. Your school is probably a convenient place to hold thedrive. It should have easy access and be visible from theroad. Arrange for a place within the school (maybe an emptyclassrooml to store the collected materials. This is especiallyimportant if you are holding the drive over a few months orcannot transport the materials to the recycling center immediately.4 . Organize transportation to haul the materials from thecollection or storage area to the recycling center.5. Publicize the drive. Make posters and/or niers to tellpeople what you are collecling. Include the date. time. andlocation of the drive. You can also contact local newspapersand radio stations to see if they will advertise the drive. Civicgroups can also help get the word OUI.6. Think about how your school can spend the money itmakes. It could be used for something the school needs. ordonated to a local wildlife center or other organization.Curbside recycling is a viable economic alternative tolandfills. Recycling aluminum cans and glass beverage containers costs Significantly less than producing them frommineral resource ores such as quartz sand and borax used

in glass. and bauxite for aluminum. [n addition, recyclingreduces costs associated with garbage disposing in landfills.Recycling benefits society and the environment by savingenergy. reducing pollution. and conserving resources. Somecommunities in California. such as San Jose. have beenparticularly successful in promoting advanced recyclingpractices of beverage containers.Remind your students to support recycling laws.Contact the California Division of Recycling (916) 3234636or (BOOl 6425669 for information on recycling....

CALIfORNIA GEOLOGY FEBRUARY 1991 39


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DMG Releases

SPECIAL PUBLICATION 103MiNES AND MINERAL PRODUC

ERS ACTIVE IN CALIFORNIA (19891990). By J.S. Rapp. M.A. Silva, C.T.Higgins. R.c. Martin. and J.L. Burnett.1990.162 p., $10,00.This is the second revised listing ofactive mines and mineral producers inCalifornia. Special Publication 103contains the names. addresses. commodities. and locations of more than

1.000 mines that were active in Cali-fornia during 1988-1989. A broadvariety of mineral recovery operationsare included in this list including: rockquarries. open pits. underground mines.gravel-bar skimming operations. brinewells. evaporation systems. and varioustypes of dredging operations. A mine

Riding an ore skip down an inclined-shafl althe Sixteen-Ta-One gold mine in the historic Allegheny mining district. Sierra County. This mine is typical 01 a Mother lode.high-grade. underground gold mine. The Allegheny mining district was discovered in1852 by Hawaiian sailors. known as Kanakas. who had "jumped ship- in San Franciscoto participate in the Cali!ornia Gold Rush. Gold mining at Allegheny began in 1852. expanded over time. and continued throughout World War II. Most o! California's othermajor gold districts closed in 1942 in response to President Franklin D. Roosevelt's WarProduction limitation Order (l-208).The Allegheny district, Including the SixteenTo-One mine. is famous for milliondollargold pockets" found there. These rich pockefs have conspicuous high-grade accumulations ot tree gold within quartz vein material. Several 01 these gold pockets, each containing more than 10,000 troy ounces. were mined at fhe SixteenTo-One mine. Mostpockets were discovered prior to 1930.The SixteenTo-One mine shut down mining operations in 1965 aHer more than 60 years of conlinuouS operation. Currently. a consortium of geologists. mining engineers. and investors is attempting to locale and discernthe character o! pocket gold deposits at the mine. The consort ium would l ike to reopenthe mine. however if is a major scientific challenge to determine where the highgradeore pockets occur. Should these miners be successful, the SiKteen-To-One mine wilt beincluded in the neKt revision 01 the DMG active mines lis\.Developers o! pocket mines like the Sixteen-To-One mine are commonly conlrontedWith obtaining and inferpreting subsurface inlormation at acceptable costs. Subsurfaceinformation is typically obtained by drilling programs that can be both expensive and limeconsuming. Photograph by J.G. Scarborough (1990).

CALIFORNIA GEOLOOY FEBRUARY 1991


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DIVISION OF MINES AND GEOLOGYP.O. Box 2980Sacramento. CA 95812-2980x

is listed as active if it produced at anylime during the two-year period fromJanuary 1988 to December 1989.

Special Publication 103. Mines andMineral Producers Actiue in California(19891990) is available at Division ofMines and Geology district offices inLos Angeles. Pleasant Hill. and Sacramento at a cost of $10.00. Makecheck or money order payable to: Division of Mines and Geology. SpecialPublication 103 may also be purchasedby mail through the:

In 1988 California produced nearly$3 billion worth of mineral commodities; California has the largest and mostdiverse mining industry in the UnitedStates. In addition to the active mineslisted in this publication. California hasseveral dozen intermittent governmentborrow pits and several thousand idleand abandoned mines and prospects.Of the 1.024 active mines in this list.681 (66 percent) are construction ag-gregate operations. 268 (26 percent)are industrial mineral mines. and 75 (7percent) are metal mines. These activemines are broadly distributed throughoutCalifornia. although much of the state'sconstruction aggregate and industrialmineral production have historicallycome from southem California.

Mine data are presented in three sec-tions sorted by 0) county. (2) mineralcommodity. and (3) company name.The Division of Mines and Geology(DMG) began updating its mineral property files in July 1988. and data for thismine list was compiled from government and private sources. The principalsource of information for this listing wasfrom files of lead agencies in California.New features of this revised publicationinclude section/township/range datawhere available. and a I: 1.000.000-scale map of California that shows thelocations and commodities of the activemines listed in the texl.

Gravity separation of scheeli te ore al the Andrew tungsten mine, los Angeles County.Scheelile is a calcium tungstate ICaWO.) and is the principal ore of tungsten. The Andrew mine is a small underground open-pit mine that produces scheelite concentratefrom thin scheelite-bearing quartz veins in granitic rock. This mine is located in theSheep Mountain Wilderness, a rugged region in the San Gabriel Mountains near LosAngeles. Although this mine is small in area, the Andrew mine is currently the largestproducer of tungsten in California.Tungsten is primarily used in steel alloys for high temperature and strength applications: such as l ight-bUlb filaments. machine tools. and advanced weaponry. Becauserelatively HUla tungsten is produced In the United States. most tungsten used in theUnited Stales must be imported from the Republic of China and other foreign sources.Small domestic metal mines such as the Andrew mine are important dispite their limitedproduction. Photograph by J.S. Rapp (1989).

CALIFORNIA GEOlOGV FEBRUARV 1991 "


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more Releases SPECIAL PUBLICATION 104

Lateral spread along Hazel Del l Road. santa Cruz County

PIKJros by the DMG Environmental ReV/ow ProJtx;t.

It was the most significant earth-quake to affect Californians since themagnilude 6.4 1971 San Fernandoquake. Although the epicentral area ofthe Lorna Prieta event occurred in asparsely populated region 01 the SantaCruz Mountains. its impact is secondonly to the 1906 San Francisco earth-quake. The greatest loss of life anddamage to property from the LornaPrieta event occurred in seismic hazardareas that had been clearly identifiedand mapped. If a similar magnitude7.I event occurred in a more denselypopulated region of California. thelosses woukl have been considerablyhigher,

An emergency session of the StateLegislature was convened from November 24. 1989 and a specia l sa les tax of1/4 percent was adopted for the periodfrom December 1. 1989 to December31 . 1990, The tax was expected toraise about $800 million. An estimated$2.9 billion in additional State and Federal assistance was needed to help thelen affected counties; about $2.3 billionwas identified for hazard mitigation

RocJdall on Eureka Canyon Roadthree days after the earthquake.In the eplCenlraJ area

THE LOMA PRIETA {SANTA CRUZMOUNTAINSJ CAUFORNIA. EARTH-QUAKE OF 17 OCTOBER 1989. Ed-ited by Stephen R. McNutt and RobertH Sydnor. 142 p. $12.00.The Loma Prieta earthquake killed63 people. injured 3.757. left over

12.000 homeless. and caused nearly $6billion in damage. A total of 23.408private homes were damaged and1.018 private homes were destroyed.A total of 3.530 businesses were dam-aged and 366 businesses were de-stroyed. Ten highway bridges wereclosed due to structural damage andthree had one or more spans collapse.Severe damage occurred 10 eightschools and eight other schools under-went substanlial damage. lnere is lilliedoubt that injuJy and damage lNeJ'e sig-nificantly lessened by the adoption andadherence of prudent building codes.

CALIFORNIA GEOLOOY fEBRUARY 1991


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Post earthquake collapse of a coaslal bluff. TunilasCreek. north of San Gregorio, San Mateo County.

It is proven that significant loss oflife and damage from earthquakes canbe reduced by enforcing modern build-ing codes. strengthening existlng structures. and maintaining an effectiveemergency preparedness program.Many of these issues are addressed inthe "Seismic Safety Element" which ispart of a city or county General Plan.Residents can consult their planningdepartment to determine the seismichazards at specific locations.

Copies of Special Publication 104are available for reference al Divisionof Mines and Geology offices in Sacramento. Pleasant Hill. and Los Angeles.Copies may be purchased from theseoffices for $12.00. Photos courtesy ofthe U.S. Geological Survey....

projects with the remainder earmarked for replacement housing. temporary shelter. and loans. Special Publication 104 isa collectlon of 14 articles representing the efforts of 35 authors. Most articles are by staff scientists of the Division ofMines and Geology. This report is divided into three sections. The first focuses on the geologic. tectonic. and seismicsetting of the quake. The second section focuses on selectedaspects of the earthquake. such as slrong motion investigations. fault evaluation. and coastal bluff landslides analysis.The third section focuses on quake response and evaluation.

There are abundant tables. photos. and illustrationsthroughout the report. Article topics were chosen to highlight Division of Mines and Geology activities and responsesresulting from the earthquake, For example. Division staffscientists participated in analyzing strong motion seismic data.conducted field investigations for evidence of surface rupture.and provided expertise to analyze quake-induced landslidesand assisted county governments to determine potential landslide risk.

The Loma Prieta event was the 11th quake of magni tude5.3 or greater to hit the San Francisco Bay area since 1865.It occurred along a 25-mile-long section of the San Andreasfault that runs through the southern Santa Cruz Mountains.When the fault broke the Pacific plate slipped 6.2 feet northwest past the North American plate and rode 4.2 feet upwards. This quake was felt by people from Los Angeles tosouthern Oregon and western Nevada.

CALIFORNIA GEOLOGY

Extensional movement across a surface fracture in the SummitRoad area, near the Santa Cruz County/Santa Clara Countyboundary. Santa Cruz Mountains.

FEBRUARY 1991


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Book ReviewsBooks reviewed III this seeMn are not available 'or purchase from DMG.

AnthropologyCALIFORNIA INDIANS: PRIMARY

RESOURCES. A Guide 10 Manuscripts.Artifacts. Documents. Serials. Music.and Illustrations. By Syliv3 BrakkeVane and Lowell John Bean. 1990.Available from: Ballena Press. Publishers Services. P.O. Box 2510. Novato.CA 94948. 399 p. $33.00. papercover. $45.00 cloth cover.California Indians are believed to bedescendants of several Asian tribes whomade their way here over the Bering

Sea land bridge al the close of the lastmajor Pleistocene glacial period perhaps 29.000 to 34.000 years ago.Evidence of early Indian culture in Cali-fornia is among the oldest data for In-dian presence in the Uniled States. Ithas been estimated that between133.000 to as many as 250.000 IncH-cms were living in California when thefirst Europeans arr ived here in the 16thcentury. This book describes how toaccess the remaining breadth of California Indian culture. A list of Indianresource materials is listed by county.

Earthquake DeSignEARTHQUAKES: An Architect"sGuide to Nonstructural Seismic Hazards. By Henry J. Lagorio. 1990.Available from: John Wiley & Sons,Inc.. 605 Third Avenue. New York,

NY 10158. 312 p. $54.95. hardcover. Price does not include sales tax.shipping, or handling.In recent years a popular adageamong California building design professionals has been MEarthquakes don't

kill people. bUildings do. Most peoplewho die during earthquakes in California are killed by collapsing structures. Afundamental problem facing engineersin California is how to design and buildstructures that can withstand the expeeted shaking from large earthquakes.However. earthquake-resistant bUildingcodes have long been practiced in Cali-fornia. They will probably improve overtime. The first spedfic seismic provisions lor earthquake-resistant design in

the United States were incorporatedinto building codes as a result of theAeld Act that was passed in 1934 bythe California State Legislature. ThisAct mandates stnet building designs forpublic schools and resulted from themagnitude 6.3 Long Beach quake of1933 that killed 120 people and causedproperty damage estimated at $41 mU-lion. In 1935 the Riley Act extendedthe requirements of the Aeld Act to allnew buildings in California. Engineersfound that Unreinforced Masonry Buildings (UMBs) nearest a major quake epicenter typically undergo the most extensive damage. In contrast, most buildingsdesigned by recent building codes holdup fairly well in large quakes.A relatively recent technological in-novation in quake design is the use ofseismic isolation: also called base isolation. Seismic isolation is a way of building structures on flexible pedestals madeof laminated rubber and steel. calledisolators. which absorb earthquakeshock. Base isolated structures are designed to slowly move for several inches

on the flexible isolators when responding to horizontal and vertical groundmovement during quakes. It is hopedthat isolators will keep overpasses fromcollapsing. people from being hurledaround inside buildings of fewer than12 stories. and plate glass windowsfrom shattering and becoming airbornerazors. In 1987 the California Office ofState Architect published MAn Acceptable Method for Design and Review ofHospital Buildings Utilizing Base lsolation.MThis manual is now used for hospital design throughout California.This book is directed primarily at

structural designers and includes chap'ters on site planning. building design.rehabilitation of existing buildings. disaster recovery, urban design and planning. nonstructural components of design, and earthquake hazards mitigationprocesses in structure design.

EnergyANNUAL REVIEW OF ENERGY.Volume IS. Edited by J.M. Hollander.R.H. Socolow. and D. Sternlighl.

1990. Available from: Annual ReviewsInc.. 4139 El Camino Way. Palo Alto.CA 94306-0897.578 p. $62.00postpaid. U.S.A. and Canada: $68elsewhere. Prepayment reqUiredHard cover.Environmental issues play an increasingly greater role in the world'senergy usage, Efnuenls from fossil fuel

consumption-the world's main sourceof energy-are rapidly becoming a serious worldwide concern. Articleswithin this book renect that concern.Articles included are about: energytechnologies such as photovohaic andnuclear. global trends In motor vehicleuse and emissions. and implementingenvironmentally sound energy sourcesfor developing countries. Extensiveliterature citations are included witheach article.

HydrogeologyPHYSICAL AND CHEMICALHYDROGEOLOGY. By Patrick A.Domenico and Franklin W. Schwartz_

1990. Available from: John Wiley &Sons. Inc .. 605 Third Avenue. NewYork. NY 10158. 824 p. $58.95.hard cover.One of the greatest natural resource

management problems facing Californiain the coming decades will be the availability. use. and quality of groundwater.Groundwater in California Is a significant resource that is instrumental to thedevelopment of this state's economy_About 40 percent of California is underlain by groundwater basins and there isan estimated 30 times more groundwater than the total surface water storagecapacity of all the reservoirs. There are449 groundwater basins of various sizesin California. The annual withdrawal ofgroundwater in California exceeds theannual recharge from rain and snow byabout 2.2 million acre-feet. The use of

" CALIFORNIA GEOlOGY FEBRUARY 1991


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Complete address form on n e ~ t page

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to consider the potential for landslideswhen designing and implementing landuse plans. Each county and incorporated dty in California must have aGeneral Plan that documents its decisions concerning the future develop-ment 01 the community. One of theseven required elements. the Safety Element (encompasses what was formerlythe Seismic Safety Element). must address the potential for "slope instabilityleading to mudslides and landslides."

AFTERSHOCK The Loma PrietaEarthquake and Its Impact on SanBenito County. By James Z. McCann.1990. Available from: Seismic Publications. 642 San Benito Street. Hollister.CA 95023. 80 p. $14.95, paper cover.

Loma Prieta Quake

SPECIAL PUBLICATIONSSP82 Mine rai commodi ty repo rl sa lt 1985 ,SP90 Minerai commod'ty reporl- talc and relaled mll 'l8rals 1986SPt03 Mines and minerai p r o d u c e ~ active in Caillornia (19891990), (NEW)SPI04 The Loma P"ela (Santa C r u ~ Mounta'nli). Cellfornla.earthquake of 17. October 1989 1990(NEW) ....

MAP SHEETS (scale 162.500)MSIS Prehmmary reconrnussance map or malOr landslides. San Gab"el Mounta,ns,Los Angeles County. Cahfornla 1969_ M531 Geology of the WiRow Creek quadrangle. Humboldt and T"mlY counties.Cahfornla 1978_ MS32 Geology of the Fallen Lear Lake (I 5') quadrangle. E' Dorado Country.Cal,forn,a 1983MS3S Kaweah Peaks Pluton and IR rela\lOnSl'llp to lhe age of the Kern Canyon faull.Tulare County. Cal,fOfIll8 1976M537 Geoklgy o! the Hamee re5llfVOlr (15'1 quadrangle. Inyo County, Caldorma. 1977

CALIFORNIA GEOLOGY1 yeal (12 ,ssues).2 y e a ~ (24 ,ssues)Each back ,ssueSpeClfy v ~ m e and month,Lisl of Ava'lable PublicatIonS

Indicate number Of topIes,SPECIAL REPORTS

SRt46 (Part I) Minefal Land c1aSSlfi(;allon: aggregate mate"als In the San FranCISCO'Monterey Bay area (cenlral Caillorma} proJOCl desenptlOll, t986SR t46 (Part II) Minerai land classlflCa\lOn: aggregate mat_ Is In !he southSan Fral1ClSCO Bay productlonconsumptlon regiQl'l {Alameda Contra Costa.San Frar1Clsco and San Mateo counties. Caillorn;a} 1988SR146 (part III) Mlneraliand classlticatlOn: aggregate malenals In the northSan FranciSCO Bay prOOUCloon-eonsumption region (Mann. Napa. andSOnoma counlleS, Califorma) 1986SRU6 (Pan IV) Minerai land classl"cat,on: aggleg.a.te materials in the MontlKey Bay- prodUCIlOllconsumplion region (Monterey, Sarl BeMO. San Mateo. Santa ClaJa.and Santa C r u ~ counlleS, Cahfornla) 1988 520 00

Landslide damage in California costsabout $250 million annually. However.due in large part to California's planning ordinances. local governments inCalifornia use landslide hazard infonnation more than local governments inmost other states. California planninglaws explidtly encourage communities

This book, a revised Ph.D. dissertation, analyzes policy approaches forpreventing or mitigating landslide hazards. Establishing and implementingland use plans and hillside gravity ordinances are two effective methods ofmoderating landslide hazards in regionsthat are prone to such threats. Thereare five illustrated examples of landslides problem areas and how local g0vernments have addressed these issues.Two examples. Blackhawk Ranch andVilla Mira Vista. are in California.

Landslides

Hydrogeology is the study ofgroundwater and its relationship to theenvironment. It is an interdisciplinarysdence that incorporales stratigraphy.petrology. chemistry. math, biology.and physics. Many scientists believethat problems concerning groundwater-such as its quantity and quality-may affect an increasing n u m ~ r ofCalifornians in the future. To protectthis vital natural resource. in currentyears there has been rapid progress inunderstanding hydrogeologic conceptsand a corresponding increase in thetechnical capability of managinggroundwater. This book reflects muchof the recent research about this fastevolving science and is designed as afundamental. although rigorous. textbook lor beginning hydrogeology students as well as profeSSionals who mayuse it for reference. A solid background in math, physics. and chemistry is recommended as a prerequisite.

groundwater in California has morethan doubled in the past 30 years; therate of its use is projected to increase.

LANDSLIDE HAZARD IN THEUNITED STATES: Case Studies inPlanning and Policy Development. ByRobert B. Olshansky. 1990. Availablefrom: Garland Publishing. Inc .. 136Madison Avenue. New York. NY10016 192 p. $47.00. hard cover

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Warehouse operations will berelocating during April.CALIFORNIA GEOLOGYsubscriptions and/or mailorders for Division publicationswill be temporarily interruptedfor about two weeks during themove. Your understanding andpatience ar e appreciated.

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Petrology

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This book reviews the general characteristics of the Archean and EarlyProterozoic basic rocks. particularly thegeochemistry and rock textures. 11 alsodraws comparisons with more recenttypes of basic rocks and the older lunarrock types. The authors discuss thevarious types of mineralization associated with the Archean and EarlyProterozoic basic rocks and the varioustypes of large basic igneous complexesthat are layered. These basic layeredigneous complexes are relatively com-

The composition of the Earth's crusthas evolved dramatically since the Archean. Key differences can be seen inbasic rock types and textures betweenthe Archean rocks and basic rocks ofsimilar chemistry from more recent geologic l imes. For example. the presentday Mid-Oceanic Ridge Basalts (MORB)are nearly the chemical equivalents tothe Archean basic rocks, yet the twoages of rocks have much different lextures due to the higher temperatures offormation of the Archean basic magmasand, in some places, metamorphic textures superimposed on the Archeanbasic rocks. The development of theEarth's crust through time is also suggested by changes in the ratio of basicto acidic rocks in continental crustthrough geologic time. For example,after the Archean Era there is a markedincrease in the amount of granitic rockover basaltic rock in the continentalcrust through the Proterozoic and Pa-leozoic eras. Thus. the Early Precambrian basic rocks should give us a modelof the Earth's crust and of tectonic activity from the earliest part of the geologic record we are able to study. 11gives us a basis for comparison with allsubsequent magmatism and crustal developments.

of the Archean and Early Proterozoiceras. which constitute the Early Precambrian. Such rocks are rarely exposed atthe surface of the Earth, but often occurin relatively small patches within thePrecambrian shields. The Precambrianshields usually serve as cores to the cantinental plates. The more recent Paleozoic, Mesozoic. and Cenozoic rocks aregenerally accreted at the edges of . or lieatop. the Precambrian shields to makeup the continents we know today.

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This book is a collection of papers bypetrologists who study Precambrianrocks, It describes, analyzes. and characterizes Early Precambrian basic igneous rocks, The study of these rocks isimportant because, (1) they are the oldest rocks we know of on Earth. (2) theygive us an idea of the original composition of the Earth's crust, (3) they give usan idea of what the early geology andtectonics were like on Earth, and (4)these rocks are frequently associatedwith massive ore deposits. The tennbasic rocks as used here includes basalts.peridotites. norites. anorthosites, andrelated igneous rocks. These rocks are

EARLY PRECAMBRIAN BASICMAGMATISM. Edited by R.P. Hall andD.J. Hughes. 1990. Available from:Routledge. Chapman & Hall. 29 West35th Street. New York. NY 10001.486 p .. $141.00. hard cover.

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The magnitude 7. 1 October 17Lorna Prieta earthquake occurred on asection of the San Andreas fault in theSanta Cruz Mountains immediatelysouth of the San Francisco Bay area.The quake released an amount of energy equivalent to about 30 million tonsof high explosives. The death toll fromthis temblor is officially listed at 67.property loss is about $8 billion: therewere 2.435 reported injuries. and about13.000 people were rendered homeless. This book chronicles the impactof the Lorna Prieta earthquake on Hol -lister and the residents of San BenitoCounty. Destructive earthquakes are afact of l ife in San Benito County andthere wil l certainly be many more. Thisbook has 150 photographs and inferviews with 75 residents.

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moo in the Precambrian shields andrelatJYeIy uncommon after Precambrian tllTle. Different occurrences ofthe early Precambrian basic rocks inmany par ts of the world on a case-bycase basts is also examined. ObservedIndMdual occurrences of Early Precambrian rocks are compared and contrasted in terms of the geologic andtectonic histories and hOVJ they rclateto the seemingly separate pieces of theEarly Precambrian geologjc puzzle.The infonnation presented leads toImplications about. and constrainlS on.our model of the early evolution of theEarth's crust. This refines our understanding of geologic events in the EarlyPrecambrian, Besides the substantialacademic interest in this topic. thereare practical potential benefits. Thesebenefits Include locating further orebOOies. eIther like the weD-knovm richdeposIts in the Precambrian shiekis. orlocating more recent ore deposits inanalogous geologic settings. Reuiewedby Dule Stickney.

fARTH SClENCE I VESnGAnONS. Edited by Margaret A Oosterman and Mark T. Schmidt 1990 Avail-able from: American Geologicallnstitute. 4220 King Street. Alexandria. VA22302. 2 34 p. $38.95. paper coverPnce includes shipping and handling.This book is designed to meet theneed of earth science teachcrs for current laboratory exercises that incorporate a Mhands on approach, and thatchallenge and motivate secondafy"-Ievelstudents. lltere are 27 exercises andeach exercise is divided into Six sections;(l)the objective of lhe exercise, (2) timerequired. (3) materials needed, (4) abackground section containing conceptsand additional resources for reference.(5) procedure. and (6) questions Asampling of exercises in this laboratorymanual include; eolian action. block diagram protems. geophysKal investigations. micro-weather pallentS. modelingcrystal growth in magmas, comparingwater hardness. determining the densityof soil panicles. determining groundwater contamination. and analyzing NonhAmerican meteorite impact sites

Plate TectonICSSHAPING TI IE EARm TECTON-ICS OF CONTINENTS A 0 OCEANS.Readings from Scientific American, Edited by Eldridge M MOOfe5. 1990.Available from: W H Freeman and

Company. 41 M a d i ~ Ave.. NewYork. NY 10010 208 p.. 1195.soft coverThe discovery of plate tectonics is

one of the most important scientificrevolutions of the 20th century. Thisbook is a collectiOn of 12 articles fromScientific American magazlnc about thelheory of plate teclonics and our current understanding of how mountains.oceans. and continents foOll. lltereare 129 ilIuslratlOns. most of which arein color. that rewallhe dynamic Eanhprocesses of plate tectonics. Plate tectonic theory was a remarkable breakthrough in effectively unifying all preVi-ously disparate branches of the earthsciences inlO a smgle world view. ThiScollection of articles-wnnen by scleotists ",,+to work at the vanguard of theirdisciplines-clearly dnd accurately explain the theory and evidence of platetectonics. This book is divided mtothree sections. the Dynamic Earth.Plates in Action. and Malong Mountains. Sec tion 1 The Dyndmic Eanh.has four anKles alxxll the continentalcrust. the oceanic crust. the Eanh's hotspots. and seismic tomography (a threedimensional analylicaltechniqlle for im -aging Earth's internal heat flow). Sec!ion Il: Plates in Action. has two aniclesabout how continents break up and oceanic fracture zones, The third. SectionIll: Making Mountains. has six articlesabout terranes, ophlohtes, the structureof mountam ranges. the Appalachians.the growth of 'NCStem Nonh America.and the fonnalkln of super continentsthrough geok>gic time (such as Pangaea). 11lere are abundant c aerialphotos. cok>r geo6ogK maps and crosssections to aSSiSt the reader in comprehending the concept presented.

5eosmologySAN FHA oseo BAY ARfAfARTHQUAKES POSTER By the staff

of the U.S. Geological Soeiety_ 1990Available from: U,S. Geological Survey.Branch of Distribution, Box 25286.Federal Center. Denver. CO 80225 24inches wide by 38 inches 1ong. $4 .00.Note; For orders less than $10.00 in-clude an addihonal $1.00. Make checkor money order payable to: Departmentof the Interior-USGS,This color poster depicts earthquakeactivity in the San Francisco Bay area.

The poster indicates eanhquake activity,the areas where it is concentrated. andhO\W the seismIc activity is associatedlAIith landform features The arca represented includes a 19.000-square-mileregiOn from lake Berryessa on thenonh 10 Monterey on the south. andfrom about 20 miles m the PacifjcOcean on the west 10 Stockton on theeast. The image was taken from 563miles above the Earth The poster m-c1udes false-color imaging to enhancethe land forms and surlace features.Various shades of red. for instance. represent areas on the ground surface thatare covered by vegetation; dark red areas indicate heavy vegetation whereaslightCT red areas show cultivated cropsLarge bOOies of water are depicted indark blue. Urbanized areas. such asmost of San Francisco. are shown inturquoise.The epicenters of more than 12.000earthquakes of magnitude 2 or largerthat occurred in the poster region from

January I. 1972 to December 31 ,1989 are shown by bright yellow dots.The magmtudes of the quakes are represented by different sized dots; earthquakes of magnitudes 2-3 are shown by1 milhmeter dots. the magnitude 7. 1Lorna Pocta eanhquake is depjctoo by a8 millimetCT dot in the Santa CruzMountains. In areas of frequent seismiCactivity, saiki yeUow lines or clustersclearly indicate lhe trace of major Bayarea faults (Hayward. Calaveras. andSan Andreas faults)."

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Announcements Union Pacific Resources Funds(AWG) Speakers Bureau

The Association for Women Geoscientists announces thatfunding is available lor the Union Pacific Resources - AWGDistinguished Lectures. Union Pacific Resources Companyhas given the AWG Foundation a $2.500 grant for 1991 tounderwrite travel for women geoscientists participating asspeakers.Grants of up to $300 for direct travel costs are availableon a first come. first served basis to nonprofit. nongovernment institutions or organizations seeking speakers from theAWG Speakers Bureau. The Speakers Bureau provides a list

of over ISO nationally recognized women geoscientists whosespecialties cover a wide range of topics.The Association for Women Geoscientists was founded in1977 to encourage women to become and remain geoscientists. AWG has chapters and at-large members throughout theU.S. and in other countries. The AWG Foundation was established in 1983 to develop and fund innovative programs designed to encourage women to study earth sciences. to inves'tigate career opportunities, and to advance in the geoscience

professions.To obtain a list 01 speakers and for information on

speakers travel. contact:Speakers BureauAssociation for Women Geoscientists Foundationc/o Resource Center for Associations10200 West 44th Avenue #304Wheat Ridge. CO 800331303) 422-8527"--

USGS Open House atMenlo Park in May

The United States Geological Survey (USGS) will host apublic open house at its campus in Menlo Park. California onMay 18-19. 1991 The exhibits and all othe r activities willexplain earth science in layperson's language.Highlights will include poster exhibits. laboratory tours.earth science videos. gold panning lessons. and mineral rec

ognition conducted by USGS mineral specialists. In addition.visitors will have the opportunity to talk with scientists whoconduct research lor the USGS. and to browse through theUSGS map store which stocks topographic maps 01 13 western states.The USGS campus in Menlo Park offers one of the mostoutstanding displays of azaleas. rhododendrons. and roses inthe Bay area. They should all be in full bloom in mid-May.For more information contact:

Peter StaufferUSGSMail Stop 919Menlo Park, CA 94025(4151 329-5100--