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UNITED STATES GEOLOGICAL SURVEY DEPARTMENT OF THE INTERIOR
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Bose from U.S. Geological Survey Hunters Point, 1968; Oakland West,
Son Francisco North, San Francisco South, 1973
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SCALE 1.24000
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CONTOU R INTERVAL 25 FEET
25'
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NATIONAL GEODETIC VERTICAL DATUM OF 1929
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MAP SHOWING THE 200 FOOT THICKNESS CONTOUR OF SURFICIAL DEPOSITS AND THE LANDWARD LIMIT OF BAY MUD DEPOSITS OF
SAN FRANCISCO, CALIFORNIA By
William B. Joyner
1982
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EXPLANATION
200-foot thickness oontour on surficiaJ deposits (hachures indicate the diYection of increasing thickness).
Landward limit of bay mud deposits
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122"20' Compiled by W.B. Joyner, 1981
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MISCELLANEOUS FIELD STUDIES MAP MF-1376
DISCUSSION
The accompanyinq map shows the 21111-foot contour of the th ickness of surf icia l deposits and the landward limit of bay muci df'posits in the City and Coun t y of San Franciscn. lt "as prepare<.! as a port of the work of the Founda t ion Design Subcommit tee of the Seismolnoy Comm it tee of the Structur~l Engineers Associc t io n of l!orthern California in connection wit h a new build inq code be i ng written by an ad hoc committee of the Association. The new code will ma ke use of tl'le fo llowrnq ~.TC-3 soil profile types (Applied Technoloqy Counci 1 , 1973):
" Soil Prof il e Type S/: Rock of any characteristic, either sha l e-like or crysta l ine in nature (such mater i al may be characterized by a shear wave ve locit_y qreater than 25nO fee t per second); or stiff soil con ditions wh~re the soil de oth is les s than 200 feet and the soil types overl_vino rock are stable deposits of sa nds, gravels, or stiffer clays.
"Soil Profile Type s2: Deep cohesionless o r stiff c l ay soil conditions, incl ud i nq sites "here the soil depth exceeds 2fl/1 feet and the soil type;s nverl.vino roe~ are stable deposits of sands, qravels, o r stiff cla.vs.
"Soi l Profile Tyoe S/: Soft.to~medium stiff clays and sands, characteri zed by 30f'et or more of snft - t o merlium-stiff clay with or withou t intervening layers of sand or other cohesionless soils.
The 200~foot thickness contour for the surficial deposits overl_yin o bedrock was deterinined by taking the diffe rence bet.,een topo9raphic contours and contours of bedrock-surface elevation on maos by Sch l ocker (1974) and Bon ill a (1954) . ln situ shear velocity measurements reported by Fumal (1978] confirm that the surficial deposits as defined by Schlocker (1974) and Bonil la (1954, 1971) are all characterized b_y values i.·ell below the 2500- foot - oersecond value ascribed to rock in the ATC-3 criteria .
The essential characteristic for s1 i s t he presence of "30 feet or more of soft to medi um sti f f clay with or without interveninq 1avers of sand or other cohesionless soils." In Sa n Fra ncisco t his ch~racte rist i c mea ns the presPnce of the hay mud deposits {Schlocker, 19 74 ). Reca11se the hay mu(( in San Francisco is near ly everywhere covered h_y artif icial fill, the best quide to the distr i but ion of ba_y mud is the historic land wa rd boundary of the marshlands as shown on thP oldest available ll.S. Coas t and 1,eodeti c Surve_y rnaps. The boundary li ne of hay mu rl on the ac cnmpa n_yin~ map was oener'all_y assumed to coincide with the l and ,,.ard houndarv of the marshlands as shown on unpublished maps on a scale of l:?4,00Q pr?oa'rerl b_y Nichnl s and ~'riqht (1971 ) from U.S. Coast and Geodetic Surve_y topOQranhic surveys dated lf\51 an rl J85?. In sor~e places, however, the bay mud below the surface extends landwarrJ from the historic marshland boundarv (McDonald and ot hers, 1978), An unpub l isherl compi la tio n of boreho le data by Ju l ius Schloder and Rrian ~t.water at 2 sc21e of 1:24,000 was used to derive the final conf i qurat ion of the mud l ine .
The line showinq the landward limit of bay mud de l imits areas where bay mud is present but d0e s not imply that all sites withi n this lim i t. are underl ai n b.v the 30 feet or mo re of soft to medium stiff clay that the ATC-3 crite r ia requ i re. Additional infonnation or fu rther assumpt i ons are reouired before s i tes within this l imit can be classified specifically as S1, S2, or S3,
Acknowlerlqments. Bri~n Ah·ater, Julius Sch 1qcke r, Dona l ~ Nic ho l s and Nancy Wriqht contr i buted 1,npublished da ta use<:J in compilinq the map; Ri cardo Zepede carefully chec ~ed and corre:ted the or iqi nal rl r aft; and the other memhers of the Foun dat ion nes i qn Subcommittee qave He benefit of their di scussion and arlvice.
f,pol i ed Techno loqy Council, seismic requlations fo r Pu hli catio~ 510, 505 p.
REFERENCES
1978, Tentative orovi sions for build1nqs: National Bureau of
the deve looment of St andards, Special
BonillJ, M. G., 1964, Bedrock - surface map of t he San Fr,rncisco Sout h qu ad:-anqle, California: U.S. t,eo ~oqical Surve_y Open-filP Report ~4-16, sca l e 1:20 ,000.
Bon il la, M. G., 1971, Prelimina ry qeo1oqic map of t he San :Crancisco South ouadranq l e and ' part of the Kunters Point ouad rannle, Cali f ornia: 11.s . Geoloaical Sur,ey Miscellaneous Fiel d St ud ies Mao MF-311, sca l e 1:?4,rlf10,
Fumal, T.'E., 1973, ·correlations between seismic WijVe vel ocities and ohysical prope rties of near - surface qeGloqic materials i n the so uthf'rn San Francisco Bay reoion, California: U.S. GeoloQical Survey Open -F ile Reoort 7R-lrJ67, ll4 p.
Helley, E. J., Lajo ie, K, ll., Spenqle, w. F., anrl Bl ai r, M, L,, 1Q7Q, Flatla n~ rleposits Df the San Francisc o Bay Pegion, California--their qeolo~_y anrl enqineering prope rties and t heir impo rtance to comprehens i ve pl anninq: U.S. Geol og i cal Surve.v Professional Paper 943, 88 r.
Mc Don al d, S. n., Nichols, D.R •• ~'ri(}ht, N. A., and Atwater, ~rian , 19711, Map showi no thickness of younq bay mud, s out hern San Francisco Bay, Cal i fornia: U.S. Geolog ica1 Survey Miscellaneous Fie 1d Studies Man MF-976, sca l e 1:125,1100.
Nichols, D.R., anrl Wright, N. A., 1971, Prel imi nar_v map of historic marqins of rrarshland, San Fran cisco bay, California: U.S. Geolo~ i cal Survey Onenrile Peport 71-216, scale 1: 125,000 .
Sch1ocker, Julius, 1974 , Geoloq_y of the San Franc isco Nor t h qu~~ranolP, Cal ifo rni a: 11 .S. Geological Survey Prof ess ional Pdoer 7P2, 1C9 p,
lnterior-Geolog1cal Surv~y, Reswn, Va.-!~82
Fo r sale by Branch uf Distribution, U.S. Geological Survey, Box 252S6, Federal Center, Denver,.CO S0225
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