MISCELLANEOUS FIELD STUDIES MAP MF–2373 U.S. DEPARTMENT OF THE INTERIOR Sheet 6 of 8 U.S. GEOLOGICAL SURVEY Pamphlet accompanies map

CORRELATION OF MAP UNITS Sierra Azul Block and related rocks in Santa Teresa Hills 20 Strike and dip of volcanic flow or of dikes and sills 1 Ball denotes that facing direction of flow is known QUATERNARY TO LATE TERTIARY UNITS Tme Shale and sandstone of Highland Way (lower Miocene to lower Eocene) MILPITAS CALAVERAS MT. DAY EYLAR MTN. MT. COPPER MTN. PATTERSON CROWS from sedimentary or volcanic structures RES. BOARDMAN LANDING 10 md gp pp af Sandstone and shale of Loma Chiquita Ridge (Eocene)Consists of: Inclined Figure 2B. References to sources of data used in compilation (see fig. 2A). Vertical Holocene Tlm Siliceous mudstone 1. Clark, J.C., field work, 1961. Qhf 2. Dibblee, T.W., Jr., Brabb, E.E., and Clark, J.C., 1978, Preliminary geologic map of the Qhb Qhl Qhfp Qhc Shear foliation or cleavage Qal Qls Qt Tls Sandstone and mudstone SAN JOSE SAN JOSE LICK ISABEL MT. STAKES WILCOX ORESTIMBA NEWMAN Laurel quadrangle, Santa Cruz and Santa Clara Counties, California: U.S. 10 Qad Qpf QUATERNARY Inclined WEST EAST OBSERVATORY VALLEY RIDGE PEAK Geological Survey Open-file Map 78-84, scale 1:24,000. Qa Qmt Qof Qaf Qoa Tcm Mottled mudstone and sandstone of Mount Chual (lower Eocene)Locally includes: Vertical 3. Burford, R.O., 1961, Geology of the Glenwood Basin area, Santa Cruz Mountains, California: Stanford, California, Stanford University graduate report, 30 p., scale Pleistocene 10 1:24,000. Tcms Sandstone lenses Joint 4. Smith, R.K., 1971, Foraminiferal studies in the lower and middle Tertiary of Soquel 5 LOS GATOS MORGAN HILL MT. SIZER MISSISSIPPI MUSTANG CREVISON Creek, Santa Clara County, California: University of California Publications in QTf Tcml Limestone Lineation directionShowing rake SANTA HOWARD QTsc TERESA CREEK PEAK PEAK RANCH Geological Sciences, v. 91, p. 1-111. Pliocene TERTIARY HILLS Great Valley Sequence (Cretaceous and Jurassic)Consists of: FoldsDashed where approximate, dotted where concealed, 5. Dupr , W.R., 1975, Maps showing geology and liquefaction potential of Quaternary Unconformity queried where uncertain deposits in Santa Cruz County, California: U.S. Geological Survey Misc. Field Studies Map MF-648, scale 1:62,500. TERTIARY AND OLDER ROCK UNITS Kus Sandstone and shale (Upper Cretaceous) Synclinal axisShowing direction of plunge 6. Clark, J.C., and Brabb, E.E., field work, 1988-89. Anticlinal axisShowing direction of plunge LAUREL LOMA PRIETA MT. MADONNA GILROY GILROY PACHECO PACHECO SAN LUIS DAM Southwest of San Andreas fault Northeast of San Andreas fault Kuc Conglomerate (Upper Cretaceous) HOT SPRINGS PEAK PASS 7. Clark, J.C., and McLaughlin, R.J., field work, 1989. Overturned syncline Santa Cruz Block 8. Sarna-Wojcicki, A.M., Pampeyan, E.H., and Hall, N.T., 1975, Map showing recently New Almaden Block KJm Mudstone (Lower Cretaceous and Upper Jurassic) Overturned anticline active breaks along the San Andreas fault between the central Santa Cruz Mountains and the northern Gablin Range, California: U.S. Geological Survey Antiformal axis Jssp Sedimentary serpentinite (Upper Jurassic) Misc. Field Studies Map MF-640, scale 1:24,000.

Pliocene 20 Tp 9. McLaughlin, R.J., field work, 1988-91. Jt Altered tuff of Mount Umunhum (Jurassic?) Outcrop-scale synclineShowing plunge Figure 1. Index map of 7.5' quadrangles in the 1:100,000 San Jose quadrangle. Area of this report indicated in red. 10. Clark, J.C., and Rietman, J.D., 1973, Oligocene stratigraphy, tectonics, and Tsc Jdb Diabase breccia of Mount Umunhum (Jurassic?) Outcrop-scale anticline paleogeography southwest of the San Andreas fault, Santa Cruz Mountains and Gabilan Range, California Coast Ranges: U.S. Geological Survey Professional Tsm 20 Paper 783, 18 p. with map and sections, scale 1:125,000.

Coast Range Ophiolite (Jurassic)Consists of: Outcrop-scale anticlineShowing plunge Unconformity 11. Dibblee, T.W., Jr., and Brabb, E.E., 1980, Preliminary geologic map of the Loma Prieta quadrangle, Santa Cruz and Santa Clara Counties, California: U.S. Jovb Quartz-keratophyre breccia and siliceous tuff (Upper and Middle Jurassic) Outcrop-scale complex folds Geological Survey Open-File Map 80-944, scale 1:24,000. Los Gatos Santa Teresa Hills Morgan Hill 20 12. McLaughlin, R.J., field work, 1988. Jov Basalt, andesite, and dacite (Middle Jurassic or older) Outcrop-scale complex foldsShowing plunge Fault 29 SCALE 1:125 000 21, 27 21, 16 21 13. McLaughlin, R.J., Simoni, T.R., Osbun, E.D., and Bauer, P.G., 1971, Preliminary ? 20 20 Tus 1 0 1 2 3 4 5 6 7 8 9 10 MILES geologic map of the Loma Prieta-Mount Madonna area, Santa Clara and Santa Tm ? Joi Intrusive complex (Jurassic) Outcrop-scale foldsShowing plunge and dip of axial plane 10 10 Miocene 1 0 1 2 3 4 5 6 7 8 9 10 11 12 KILOMETERS Cruz Counties, California: U.S. Geological Survey Open-File Map, scale Ttv 16 Tlo 1:24,000. K-Ar 16 sc 15.6 Ma Jog Gabbro cumulates (Jurassic) Outcrop-scale complex folds Showing dip of axial plane 9 10  Unconformity Tms 21, 16 28 14. Osbun, E.D., 1975, Geology of the Sveadal area, Southern Santa Cruz Mountains, 27 24 32 20 21 California: San Jose State University, M.S. thesis, 156 p., with map, scale ? 16 Jou Ultramafic cumulates (Jurassic) Outcrop-scale complex foldsShowing plunge and dip of axial plane 1:12,000. ? 10 La Honda Sierra Azul Fault 31,32 15. Simoni, T.R., Jr., 1974, Geology of the Loma Prieta area, Santa Clara and Santa Cruz Subsidiary Block and TERTIARY Jos Serpentinized ultramafic rocks (Jurassic) 30 Oil drill hole surface location Counties, California: San Jose State University, M.S. thesis, 75 p., with map, scale Block related rocks in 16 21 Santa Teresa 21 1:12,000. ? Hills Jsl Slate of Loma Prieta Peak (Jurassic?) Subsurface course of abandoned railroad tunnel southwest of Wright 9 16 16. Bailey, E.H., and Everhart, D.C., 1964, Geology and quicksilver deposits of the New Tla 31 Almaden District, Santa Clara County, California: U.S. Geological Survey Tt dbc Diabase of Corralitos Creek (lower Miocene or Jurassic) Earthquake mainshock epicenterOctober 17, 1989 8, 19 Professional Paper 360, 206 p. Minor modifications to geology by McLaughlin, Loma Prieta earthquake. Located in southeastern Laurel R.J., 1990-96. Also, Stanley, R.G., and McLaughlin, R.J., 1995-97, field work 32 Tv ? ? quadrangle. Focal depth was 17 km (see text discussion) MAP and sampling for petroleum source rock and biostratigraphic studies. Tvb Southwest of San Andreas fault 16 dbc2 ? ? Tz 2 Santa Cruz Block A' dbm Unconformity 17. Brabb, E.E., field work, 1969. ? ? 18, 20, 22, 23, 26 A Locations of structure sections shown on geologic maps Oligocene Tp Purisima Formation (Pliocene and upper Miocene) 9, 17 8, 19, 23, 26 18. Clark, J.C., and Brabb, E.E., field work 1990-91. Tme 32 Tsr Mine adit 9 31 21 Tlm Tsc Santa Cruz Mudstone (upper Miocene) 19. Clark, J.C., and McLaughlin, R.J., field work, 1990-91. 18, 20 9, 25 9 9 Tst 31 Ben Lomond Mine shaft 33 20. Dibblee, T.W., Jr., and Brabb, E.E., 1978, Preliminary geologic map of the Los Gatos Tls Tsm Santa Margarita Sandstone (upper Miocene) Subsidiary 8, 9 12, 13 Quadrangle, Santa Clara and Santa Cruz Counties, California: U.S. Geological Eocene Block 32, 35 Survey Open-File Report 78-453, scale 1:24,000. Tbm 2, 7, 8 Tbu Oil seep Tcms Tm Monterey Formation (middle Miocene) Tbc Tbs 21 BOUNDARY 21. Helley, E.J., photogeology and field checking, with additions by McLaughlin in Tcm 12, 13, 15 21 34 uplands, tributary stream valleys, and along valley margins, 1989-91. Base not exposed Quarry 32, 33 Unconformity Fault Tcml 1, 2 Fault Tlo Lompico Sandstone (middle and lower Miocene) 22. Johnson, R.E., and Associates, 1989, Fault investigation report, Loma Prieta Paleocene 32, 35 32, 36 Elementary School, Santa Clara County, California: Loma Prieta School District La Honda and Ben Lomond Subsidiary Blocks Trench siteshown locally 12, 13, 14 32,33,36 21 Open-File Report, 50 p. Great Valley Sequence Franciscan Complex Tla Lambert Shale (lower Miocene) 2, 3, 4, 5, 6 32, 36 21 32, 34 Area of hydrothermal alteration 6, 8, 11, 12 23. Keefer, D.K., 1991, Geologic hazards in the Summit Ridge area of the Santa Cruz bs v ? 32, 36 Mountains, Santa Cruz County, California, evaluated in response to the October Tv Vaqueros Formation (lower Miocene and Oligocene)Locally includes: 17, 1989, Loma Prieta Earthquake: Report of the technical Advisory Group: U.S. Kus ch 33, 36 Geological Survey Open-File Report 91-618. LandslideArrows indicate direction of movement 32, fm Tvb Basalt flows (upper Oligocene) Kuc 34 34 am 24. McLaughlin, R.J., and Harden, J.W., Site visit to Shannon fault trenched by Emcon Qls ? 12, 13 Associates, 1989. Fault cg mdi Kgr Fault Tz Zayante Sandstone (lower Miocene and Oligocene) 21, 5, 32, 33 ? fpl Rotational block-style landslideArrows indicate 5, 6, 10, 11 25. McLaughlin, R.J., Loma Prieta earthquake investigation, surface deformation data, fms CRETACEOUS direction of movement, hachured line indicates 1989. San Lorenzo Formation (Oligocene and Eocene)Consists of: Qls block boundary 32 21 fpv Unconformity 32, 35 26. Ponti, D.J., and Wells, R.E., 1991, Off-fault ground ruptures in the Santa Cruz Mountains, California: Ridge-top spreading versus tectonic extension during the Tsr Rices Mudstone Member (Oligocene and late Eocene) fpt Fault 1989 Loma Prieta earthquake: Bulletin of the Seismological Society of America, KJm Tvb Rotational block-style landslideShowing coherent 32 32, 33, 35 34 v. 81, p. 1480-1510. Qls unit mapped within landslide block 34 Tst Twobar Shale Member (late Eocene) 35 27. Sorg, D.H., and McLaughlin, R.J., 1975, Geologic Map of the Sargent-Berrocal fault Fault Laurel Loma Prieta Mt. Madonna Gilroy zone between Los Gatos and Los Altos Hills, Santa Clara County, California: U.S. Fault Butano Sandstone (Eocene)Consists of: Geological Survey Miscellaneous Field Investigations Map MF-643, scale Sag pond 1:24,000. Jssp Figure 2A. Index to sources of geology, southwestern Santa Clara Valley and southern Santa Cruz Mountains. Numbers are keyed to reference list (fig. 2B). Fault Jsl ? Tbu Undivided sandstone and shale (late to middle Eocene) fmc 28. Short, W.R., Jr., 1986, Geology of the Santa Teresa Hills, Santa Clara County, Jt California: California State University, Hayward, M.S. thesis, 112 p., with minor Jdb modifications and field checking by McLaughlin, 1991. Tbm Mudstone (late Eocene) Coast Range ophiolite Fault Jmb3 2 2 29. Coleman, R.G., 1991, unpublished mapping. Also, see Coleman, R.G., 1991, dbm dbc Jovb JURASSIC Joi Serpentines of Santa Clara Valley, California [abs.]: Geological Society of Jov ? Tbs Sandstone (middle Eocene or younger) Pb-U America Abstracts with Programs, v. 23, no. 2, p. 15. ? ? Jog ≥ 168 Ma ? 1 Jou Tbc Conglomerate (middle Eocene or younger) Monte Vista - Piercy? 30. McLaughlin, R.J., and Elder, W.P., field work with J.L. Nelson and R. Baker, See DESCRIPTION OF MAP UNITS in accompanying Jos Jos Santa ? Major fault block boundaries pamphlet for specific unit age assignments. Terratech, 1991. Clara ? 2 Fault Kgr Granitic and metamorphic rocks (Cretaceous and older) Fault? See Diabase of Corralitos Creek and Diabase and gabbro of fmv Valley FaultDotted where concealed, queried 31. Dibblee, T.W., 1973a, Preliminary geologic map of the Morgan Hill 7.5' quadrangle, ? SANTA ? Morell Cutoff Road and Laurel Creek in DESCRIPTION OF where uncertain. Horizontal arrows Santa Clara County, California, U.S. Geological Survey Open-File Report, scale MAP UNITS in accompanying pamphlet. ? denote relative horizontal movement 1:24,000. 3 Fault Jmb Mafic basement rocks (Jurassic)shown only on structure sections TERESA Subsurface unit; shown only in cross sections. ? Shannon ? Thrust faultBarbs on upper plate ? OUTLIERHILLS 32. McLaughlin, R.J., field mapping investigations, 1996. ? Fault ? dbm Diabase and gabbro of Morrell Cutoff Road and Laurel Creek ? ? FoldsDotted where concealed 33. Dibblee, T.W., 1973b, Preliminary geologic map of the Mt. Madonna 7.5' (lower Miocene or Jurassic) Berrocal ? Zone quadrangle, Santa Clara and Santa Cruz Counties, California, U.S. Geological MAP Synclinal axis, showing direction of plunge LIST OF MAP UNITS Survey Open-File Report, scale 1:24,000.

Fault

[See pamphlet for Description of Map Units. Some unit exposures on the plotted maps are too small to EXPLANATION Soda ? Anticlinal axis, showing direction of plunge n ?

[See database for structural detail that is not shown clearly on printed maps] o distinguish the color for unit identification. These units are labeled where possible, and unlabeled units t 34. Dibblee, T.W., 1973c, Preliminary geologic map of the Gilroy 7.5' quadrangle, Santa

TERTIARY AND OLDER ROCK UNITS g n Antiformal axis are attributed in the database] i S Clara County, California, U.S. Geological Survey Open-File Report, scale

Northeast of San Andreas fault x p NEW

ContactDashed where approximate, dotted e rin gs

New Almaden Block L 1:24,000. 36 where concealed, queried where uncertain Fault SantaBOUNDARY QUATERNARY TO LATE TERTIARY UNITS Negative gravity anomaly associated sc Silica-carbonate rock (Miocene?) Fault ALMADEN with Cupertino sedimentary basin 35. McLaughlin, R.J., 1971, Geologic Map of the Sargent Fault zone in the vicinity of U Mt. Mount Madonna, Santa Clara County, California, U.S. Geological Survey Basic Fault Dashed where approximate, dotted Aldercroft Umunhum md Mine dump (Holocene) D  Fault 10 where concealed, queried where uncertain. Data Contribution 13, scale 1:12,000. Tus Unnamed sandstone (middle Miocene or younger) Quaternary deposits of Santa Clara Valley U and D denote upthrown and downthrown Butano Hooker Gulch Fault 36. Jov -Col n, C.F., 1991-92, field work while graduate intern with U.S. Geological gp Gravel pit (Holocene) blocks. Arrows with (without) numbers denote UVAS fault dip (or dip direction). Bar and ball locally Sierra Azul Fault Survey, with field checking by McLaughlin, R.J., in 1996. Tms Monterey Shale (middle and lower Miocene) Fault Sierra BLOCK Clara Earthquake mainshock epicenterOctober denote downthrown block. Horizontal arrows SIERRA A NT 17, 1989 Loma Prieta earthquake pp Percolation pond (Holocene) denote relative horizontal movement. Double IF Azul O barb denotes vertical fault R Tt Temblor Sandstone (middle Miocene to Oligocene?)Locally includes: Fault M La Berrocal af Artificial fill (Holocene) Sargent San Ttv Volcanic and intrusive rocks (middle Miocene) Attenuation faultFault at low angle to bedding, Loma Prieta Pk. interpreted as low-angle normal fault, double Valley Qal Alluvium, undivided (Holocene and Pleistocene) hachures on down-dropped (upper plate) side. Laurel AZUL Fault UVAS Jos Serpentinized ultramafic rocks (Jurassic) Dashed where approximate, dotted where concealed, queried where uncertain Honda Andreas Qls Landslide deposits, undivided (Holocene and Pleistocene) Glenwood Fault ANTIFORM Franciscan Complex (Cretaceous and Jurassic)Consists of: Zayante Thrust faultBarbs on upper plate. Dashed Anticline Berrocal Qt Alluvial terrace deposits, undivided (Holocene and Pleistocene) where approximate, dotted where concealed, SANTA MAP fm Melange of the Central belt (Upper Cretaceous)Includes: queried where uncertain SubsidiaryFault Qhf Alluvial fan deposits (Holocene) BLOCK Santa bs Blueschist blocks Principal trace of the San Andreas faultDashed CRUZ Fault Mt. Madonna where approximate, dotted where concealed Syncline Qhb Basin deposits (Holocene) ADAMS am Amphibolite blocks Ben BOUNDARY U Crack, 10/17/89Surface crack that occurred SCHOOL D Valley Qhl Levee deposits (Holocene) 10 during the Loma Prieta earthquake of October 17, Subsidiary Fault Zone ANTIFORM ch Chert blocks 1989. U and D denote upthrown and downthrown Lomond Clara blocks. Arrow and number denote dip. Bar and BLOCK Qhfp Floodplain deposits (Holocene) ball locally denote downthrown block v Basaltic volcanic rock blocks

Qhc Stream channel deposits (Holocene) g g g g g g g g g g g g g Glauconitic marker block cg Conglomerate block block Qa Aromas Sand (Pleistocene)Locally divided into: Conglomeratic marker mdi Metadiorite block

Qad Dune deposits Photo lineament Permanente terrane (Cretaceous)Divided into: SCALE 1:125 000 1 0 1 2 3 4 5 6 7 8 9 10 MILES Qaf Fluvial deposits Marker bed fpl Foraminiferal limestone (Upper and Lower Cretaceous) 1 0 1 2 3 4 5 6 7 8 9 10 11 12 KILOMETERS

Qof Old floodplain deposits (Pleistocene?) Strike and dip of bedding fpv Volcanic rocks (Lower Cretaceous) Figure 3. Major fault blocks of the southwestern Santa Clara Valley and southern Santa Cruz Mountains. Stratigraphy of fault blocks is discussed in map text and in rock descriptions. 10 20 InclinedBall denotes that facing direction Qmt Marine terrace deposits (Pleistocene) is known from sedimentary structures; fpt Siliceous radiolarian-bearing tuff no dip means dip unknown

Qoa Old alluvium, undivided (Pleistocene) VerticalBall denotes that facing direction Marin Headlands terrane (Cretaceous and Jurassic)Divided into: is known from sedimentary structures Qpf Alluvial fan deposits (Pleistocene) Horizontal fms Sandstone (Upper and (or) Lower Cretaceous) 10 20 OverturnedBall denotes that facing direction QTf Fluvial deposits, undivided (Pleistocene and Pliocene?) is known from sedimentary structures fmc Radiolarian chert (Lower Cretaceous and Jurassic) Approximate Based on photo interpretation 20  QTsc Santa Clara Formation (Pleistocene and Pliocene) or estimated dip in field Edited by J.L. Zigler fmv Basaltic volcanic rocks (Lower Jurassic) Manuscript approved for publication July 20, 2001 20 In trenchMeasured from exposures at geotechnical or construction trench site Any use of trade, firm, or product names in this publication is for descriptive purposes only and does not imply endorsement by GEOLOGIC MAPS AND STRUCTURE SECTIONS OF THE SOUTHWESTERN SANTA CLARA VALLEY AND the U.S. Government. This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic SOUTHERN SANTA CRUZ MOUNTAINS, SANTA CLARA AND SANTA CRUZ COUNTIES, CALIFORNIA plotters and between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map.

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