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42 33 47 17 44 30 30 39 33 28 76 53 19 46 40 35 30 50 18 37 37 25 47 57 83 40 30 43 15 43 40 45 35 85 41 59 67 54 85 43 46 41 60 19 55 57 62 70 41 55 30 50 55 61 67 67 9 35 35 57 40 38 55 20 50 35 35 37 44 15 52 24 33 50 26 15 77 31 86 39 52 71 27 15 57 65 25 30 35 68 53 28 33 19 26 12 36 22 82 46 12 45 15 39 15 8 22 15 30 11 63 37 5 11 15 40 39 48 30 16 33 24 18 32 56 30 35 28 47 48 20 26 54 49 62 43 39 35 25 75 35 37 47 78 27 37 8 38 27 9 19 30 42 32 30 68 56 53 35 28 24 22 24 18 19 24 18 25 30 32 44 33 49 44 14 23 30 45 19 15 28 26 19 27 18 29 35 35 68 43 25 20 25 59 22 30 25 23 32 40 33 40 8 65 51 59 7 17 28 23 21 26 25 13 16 39 13 12 28 45 35 20 35 62 25 44 37 25 20 51 29 52 44 23 26 30 14 18 73 49 34 12 45 39 51 29 28 21 32 42 30 43 37 39 32 31 35 40 42 32 40 28 32 31 42 30 43 44 44 42 50 87 69 78 53 44 48 22 22 50 40 36 43 37 31 50 44 56 48 19 36 24 27 30 27 33 34 22 86 42 33 40 25 15 50 45 44 2 6 10 8 3 3 5 23 4 65 25 20 10 5 13 6 10 7 15 30 24 20 13 41 43 35 15 43 17 11 47 32 34 32 27 47 50 53 15 24 14 16 23 22 25 19 33 10 17 19 50 44 8 14 14 10 23 13 13 26 34 54 62 17 12 35 27 6 9 26 35 24 30 4 Jsp KJfv Qls ch KJfc Qls Qls sc Qls Qls Kfs gw ch Kfm Jsp KJfv Qls Qls Jsp Tm Qls Jsp Tv Qls Qya Tm KJfg Kfm Tv Qls Qls Qls KJfg Kfm Tv Qls KJfg Jsp Qls KJt KJt Tv Tv Kfm Tm Qls Kfm Tv Qd sc Qya Kfs Kfm Kfm Tpm sc Qls Tpe Qya Qls Tpm Qls mv ch Jsp Jsp KJfv mv Jsp Tpe Tpm Kfm Qls Jsp Jsp Qls Qls Qya Qb Tv Jsp Kfm Tmd Tmd Qls Qls Tpm Qls Qls Qya Tm KJfv Qls Qls Tm Kfm Qls Kfs Qls Qop Qls Qls mv Qls Kfm mv Jsp sc Qya Qls Qls Qls Qya Qya Qa Qls Qya 2 Qls Qop ch Tpe sc Qls Tpe Jsp Kfm Qls Qls sc Jsp ch bs KJfv gw ch Kfm Tpe Tv Kfm Jsp KJfv KJfc Qls Qls Jsp Qls Tpm Jsp Tpe Qls KJfv Tpm Qls Tpe KJfv ch Qls KJfv Qya 2 Qls Kfm Qls sp Tm Qls Qls Tv Qls Tm Qls KJfv Kfm Jsp Qls Qls Qls sp Tv Qls Qls KJfv Qls Qls Qls Qls Qls Qls Qls Qls Qya Tm Qls Qls Qls Qls Qls KJfv Jsd Qls Tv Qls Qls Qls Qls Qls Qls Jsp Tv Qls Qls Qls Tm Tv Qls Qls Qls Qls Qls Qya 2 Qls mv Qya 2 Qya 1 Qls Jsp Qls Qls mv Qls Qya 2 Qls Qls Qls KJtc Qls Qya 1 Jsp Qya 1 Tv Qls Qls Qya Qls Kfm Qya 1 Jsp Qya 1 Jsp mv Qls Qya 2 Qls Qls Jsp mv Qls Jsp Qls mv Tv Qls Tmt Qls Qls Qls Jsp sp Qls Qls Qls Kfm Qls Qls Qya Qls Qls Qls Qls Qls Jsd mv Qls Jch Jsd mv Jbd Jch ch Kfm Qls Jch Tv Qya Qls Qls mv Qls KJtc Qls KJtc KJfv KJtc Qls Jsp Jsp Qls Kfm Qls Qls sc mv Qls Qls Qls Qls Jbd Tdb Qls Qls Kfm Tdb Qya Qls Jsp Tr Qls sc Qls Qls KJfg mv Tr sp Qls Qls KJtc Tdb Qls Qls Qls Qls Qls KJt mv Qya Qya Qls Tdb Jsd Tr sc Kfm Jsp sc Qya Qls Jch Tdb Qls Qya KJtc Kfm O C E A N I C Kac Kfm Qls Qya Tr Qls Tdb Qls Qya sc Tr Tf Qya KJtl Jsp sc sc KJtc KJtc Kfm Jsp Tdb Tdb Kfm Qls Tr Qls Qls sp Qya Tcg Tdb ch Kac sp Kfm Qls ch Ka mv sp Qls Kfm Ka mv Qls Qls Tf Qls Qls Tdb Qls KJfg Qls mv Kac Kfm Tft sc Tv KJt Tv Tf Tv Qls Tf Tft sc KJt Kfm sp Qls Tdb Tdb Tr Tf Tcg Qya KJt Tv Tm Qya Kfm Ka Kac Ka Kfm Tv Qls KJtl KJtl Qls Qls Qls Qls KJt Qls Qls Kfm Kfm Jsd F A U L T Z O N E Jbd Tm Tf Tr Qya Kfm KJfv Tm Tm Kfm Jbd Jch APPROXIMATE MEAN DECLINATION, 2016 0 0 0 1 1 1 .5 .5 2 2 2 Thousand Feet Kilometers Miles Scale 1:24,000 Contour Interval 40 feet Supplementary Contour Interval 10 feet National Geodetic Vertical Datum of 1929 12.9° TRUE NORTH MAGNETIC NORTH STATE OF CALIFORNIA – EDMUND G. BROWN JR., GOVERNOR NATURAL RESOURCES AGENCY – JOHN LAIRD, SECRETARY FOR NATURAL RESOURCES DEPARTMENT OF CONSERVATION – DAVID BUNN, DIRECTOR CALIFORNIA GEOLOGICAL SURVEY JOHN G. PARRISH, Ph.D., STATE GEOLOGIST PRELIMINARY GEOLOGIC MAP OF THE MORRO BAY NORTH 7.5’ QUADRANGLE, CALIFORNIA Copyright © 2016 by the California Department of Conservation, California Geological Survey. All rights reserved. No part of this publication may be reproduced without written consent of the California Geological Survey. "The Department of Conservation makes no warranties as to the suitability of this product for any given purpose." PRELIMINARY GEOLOGIC MAP OF THE MORRO BAY NORTH 7.5' QUADRANGLE SAN LUIS OBISPO COUNTY, CALIFORNIA VERSION 1.0 By Mark O. Wiegers Digital Preparation by Mark O. Wiegers and Marc Delattre 2016 This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program, Statemap Award no. G15AS00006 35°30'00” 120°54’00'' 35°22'30'' 120°45'00” 35°30'00” Coordinate System: Universal Transverse Mercator, Zone 10N North American Datum 1927. Topographic base from U.S. Geological Survey Morro Bay North 7.5-minute Quadrangle, 1965 (Revised 1993). Shaded relief image derived from USGS 1/3 arc-second National Elevation Dataset (NED). 120°52'30” 120°52'30” 35°22'30'' Professional Licenses and Certifications: M.O. Wiegers - PG No. 4157, CEG No. 1506 Preliminary Geologic Map available from: http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm (Pa (P (Pa Paso s s Robles les) ) ) (Paso Robles) - Adjacent 30’ x 60’ quadrangles (T ( (T (T Taft) (Sa (Sa (Sa (Sa (Sa Sa ( ( (Sa S nta nt nt nta nt n nta n M M Ma M ria) 135 58 41 229 227 166 46 1 101 Santa Maria 1 5 Kilometers 5 Miles CAYUCOS MORRO BAY NORTH MORRO BAY SOUTH PORT SAN LUIS PISMO BEACH ARROYO GRANDE NE PE LO LO LO LO LO LO OPE PE PE PE PE P P PE PE PE PE PE PEZ Z Z Z Z Z Z M M M M M M M MT MT MT MT MT MT MTN N N N N N N TA TA TA TA TA T TAR R R R A A A AR R R R R SP SP SP SP SP SP SP SP S SP SP SP SP SP SP SP SPRI RI RI RI RI R R NG NG NG NG NG R RI RI RI RI RI RI RI R DG DG DG DG DG DG DGE E E E E E E E E E E E E E CA CA CA CA CA CA CALD LD LD LD LD LD LDW W W W LD LD LD LD LD LD LDWE WE WE WE WE WE WELL LL LL LL LL LL LL ME ME ME ME ME ME MESA SA SA SA SA SA SA LO LO LO LO LO LOS S S S O O O O OS S S S S S S MA MA MA MA MA MA MA MA MA MA M CH CH CH CH CH CH CHOS OS OS OS OS OS OS HI HI HI HI HI HI HILL LL LL LL LL LL LLS S S S S S S S S S S S S S BR BR BR BR BR RA A A A A A R R R R RAN AN AN AN AN AN A CH CH CH CH CH H MT MT MT MT MT MT MTN N N N N N MI MI MI MI M MI M MI MI MI MI MI MI MIRA RA RA RA RA RA RAND ND ND ND ND ND NDA A A A A A A A A A A A A A PI PI PI PI PI PI PINE NE NE NE NE NE NE E E E E E E E M MT MT MT MT M MT MT MT MT MT MT MTN N N N N N H H H H H H HU HU HU HU HU HU UAS AS AS AS AS AS ASNA NA NA NA NA NA NA PE PE PE PE PE PE PE PEAK AK AK A AK AK AK AK A AK AK AK AK AK K K K NIPOMO OCEANO CH CH CH CH CH CH CH CH CH CH CH CH CH CHIM IM IM IM IM IM IM M M M M MNE NE NE N N NE NE NE N N N NEY Y Y Y Y Y Y Y Y Y Y CA CA CA CA CA CA CANY NY NY NY NY NY NY Y Y Y YON ON O ON ON ON O ON O Y Y Y Y Y Y Y YON ON O O ON ON ON ON ON O O SANTA MARGARITA TA SA SA SA SA SA SA SA A A A ANT N NT NT NT N N N N A A A A T TA A A A RGA MA MA MA MA MA MA A A MA MA MA MA MARG RG RG RG RG R R R RGA A A A RG RG RG R RGAR AR AR AR AR RIT IT IT IT IT IT A A A A A LA LA LA LA LA A AKE KE KE KE KE WI WI WI WI WI W WI W LS LS LS LS S LS LSON ON ON ON ON ON N N N N N CO CO C CO CO C C C RN RN RN RN RN RN RN RN RN RN N NER ER ER ER ER C CA CA CA CA CA CA CA AMA MA MA MA MA MA MA MATT TT TT TT TT TT TT A A A A T T T T A A A A TTA 5 8 RA RA RA RANC NC NC NC A ANC NC NC NCH H H H ZO PO PO PO PO PO PO POZO ZO ZO ZO ZO ZO ZO ZO ZO ZO ZO ZO O O UM SU SU SU SU UM M M M U U U UMM MM MM MM MM M IT IT IT IT T LA LA LA LA P P P P P P PAN AN AN AN AN AN ANZA ZA ZA ZA ZA ZA ZA ZA ZA ZA ZA ZA ZA RA RA RA RA A A ANC NC NC NC A A A ANC NC NC NCH H H H PA LA LA LA LA LA LA LA P P P P P P PA A A A A P P P PAN AN AN AN AN AN NZA ZA ZA ZA Z ZA ZA FO CA CA CA CA CA CALI LI LI LI LIFO FO FO F FO FO FO FO O O ORN RN RN RN RN RN RNIA IA IA IA IA IA I V V V V V VA VA VA VALL LL L LL LL L LEY EY EY EY EY EY E LA LA LA L P P PAN AN A ZA ZA Z ZA ZA NE NE ATASCADERO Mapping completed under STATEMAP Previous projects since 2008 FY 2015-16 SAN LUIS OBISPO Other new mapping by CGS FY 2015-16 121°0’0” 120°30’0” 120°0’0” 35°30’0” 35°0’0” San Luis dra ra dra rangl ng ngl ngl ngle e e e e n n Lu Luis is Obi Obispo spo n Luis Obispo 30 30’x6 ’x6 ’x60’ 0’ 0 qua qua30’x60’ quan d REFERENCES Chipping, D.H., 1987, The Geology of San Luis Obispo County, A Brief Description and Field Guide: unpublished field guide by Cal. Poly. geology instructor. Clark, D.G., Slemmons, B., Caskey, J.S. and dePolo, D.M., 1994, Seismotectonic framework of coastal central California, in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B, eds. Seismotectonics of the Central California Coast Ranges: Geological Society of America Special Paper 292, p. 9-30. Dibblee, T.W. (and Minch, J.A., ed.), 2006, Geologic map of the Morro Bay North quadrangle, San Luis Obispo County, California: Dibblee Geological Foundation, Dibblee Foundation Map DF-215, scale 1:24,000. Dibblee, T.W. (and Minch, J.A., ed.), 2006, Geologic map of the Cayucos quadrangle, San Luis Obispo County, California: Dibblee Geological Foundation, Dibblee Foundation Map DF-216, scale 1:24,000. Graymer, R.W., Langenheim, V.E., Roberts, M.A. and McDougall, Kristen, 2014, Geologic and Geophysical Maps of the Eastern Three-Fourths of the Cambria 30’ x 60’ Quadrangle, Central California Coast Ranges: U.S. Geological Survey Scientific Investigation Map 3287, scale 1:100,000. Hall, C.A., Jr., Ernst, W.G., Prior, S.W., and Weise, J.W., 1979, Geological map of the San Luis Obispo-San Simeon region, California: U.S. Geological Survey Miscellaneous Investigations Series Map I–1097, scale 1:48,000. Hall, C.A. , and Prior, S.W., 1975, Geologic map of the Cayucos – San Luis Obispo Region, San Luis Obispo County, California: U.S. Geological Survey Miscellaneous Field Studies, Map MF-686, scale 1:24,000. Hanson K.L., Wesling, J.R., Lettis, W.R., Kelson, K.I., Metzger, L., 1994, Correlation, ages, and uplift rates of Quaternary marine terraces: South-central coastal California, in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B, eds. Seismotectonics of the Central California Coast Ranges: Geological Society of America Special Paper 292, p. 45-71. Hart, E.W., 1977, K-Feldspar in Upper Mesozoic Sandstone Units Near Atascadero, Santa Lucia Range, San Luis Obispo County, California; California Division of Mines and Geology Special Report 128. Hsu, K.J., 1976, Preliminary report and geologic guide to Franciscan mélanges of the Morro Bay-San Simeon area, California: California Division of Mines and Geology Special Publication 35, 46 p. Lettis, W.R., Kelson, K.I., Wesling, J.R., Angell, M., Hanson, K.I. And Hall, N.T., 1994, Quaternary deformation of the San Luis Range, San Luis Obispo County, California, in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B, eds. Seismotectonics of the Central California Coast Ranges: Geological Society of America Special Paper 292, p. 111-132. Page, B.M., 1972, Oceanic Crust and Mantle Fragment in Subduction Complex near San Luis Obispo, California: Geological Society of America Bulletin, v. 83, p. 957-972. Seiders, V.M., 1982, Geologic map of an area near York Mountain, San Luis Obispo County, California: U.S. Geological Survey Miscellaneous Investigations Series I–1369, 1 sheet, scale 1:24,000. Snow, C.A., and Shervais, J.W. 2001, Cuesta Ridge Geologic Map, Unit Descriptions and Relationships, in 2001 EDMAP project “Geologic Mapping in the San Luis Obispo Urban Area: The Coast Range Ophiolite and Franciscan Complex in Central California, and the Influence of Bedrock Geology on Surface Processes.” Remote Sensing Data: PG&E Diablo Canyon Power Plant, San Simeon, CA Central Coast, Airborne Lidar: OpenTopography web portal, DOI: 10.5069/G9CN71V5, OT collection ID: OT.032013.26910.2, raster resolution 1 meter, survey date 02/07/2013 to 2/25/2013. 30 s 30 ? Contact between map units - Solid where accurately located; dashed where approximately located; dotted where concealed Fault - Solid where accurately located; dashed where approximately located; short dash where inferred; dotted where concealed; queried where identity or existence is uncertain Thrust fault - Solid where accurately located; dashed where approximately located; dotted where concealed; queried where identity or existence is uncertain. Barbs on upper plate Synclinal axis - Solid where accurately located; dashed where approximately located; dotted where concealed Anticlinal axis - Solid where accurately located; dashed where approximately located Strike and dip of bedding plane Strike and dip of overturned bedding Landslide - Arrows indicate principal direction of movement MAP SYMBOLS ? Qa Qls Qya Qop Tr Tpm Tpe Tf Tcg Tft Tdb Kfm Tv Kfs KJt KJfg KJfc KJfv DESCRIPTION OF MAP UNITS SURFICIAL UNITS Beach and active dune deposits (late Holocene)—Unconsolidated, mostly fine- and medium-grained sand accumulated along the coastline; includes scattered cobbles. Dune sands (late Holocene)—Unconsolidated, well-sorted white to brown windblown sand. Forms active dunes behind modern beaches. Alluvial flood plain and channel deposits (late Holocene)—Active stream channel and recently active flood-plain deposits. Consist of unconsolidated, silty sand and sandy gravel with cobbles, scattered boulders with occasional lenses of silty clay. Landslide deposits (Holocene to late Pleistocene)—Includes comparatively shallow earth flow and debris slide deposits consisting of fragmented bedrock and soil mixtures, and deep rock slides of relatively intact bedrock displaced along rotational or translational slip surfaces. Most prevalent in ophiolitic serpentinite along the Oceanic Fault and in Franciscan melange. Young alluvial flood-plain deposits, undivided (Holocene to late Pleistocene)—Unconsolidated sand, silt and clay-bearing alluvium deposited on flood-plains and along valley floors. Surfaces on young deposits are undissected and lack soil development. Surfaces on older deposits are slightly dissected and display weak soil development. Locally divided by relative age (2 = youngest, 1 = oldest): Young alluvial valley deposits, Unit 2 Young alluvial valley deposits, Unit 1 Old paralic deposits (late Pleistocene)—Marine terrace deposits consisting of beach and nearshore sands and gravels covered by colluvium and alluvium. These deposits rest on an emergent wave-cut platform preserved by regional uplift just north of Morro Bay. Marine deposits consist of well-sorted sand and gravel locally containing fossils and shell fragments. Overlying non-marine cover consists of poorly-sorted sand, silt, gravel and clay deposited by slope wash and alluvial processes. Estimated age of the wave-cut platform is 120 ka (Hanson and others, 1994). TERTIARY ROCKS Pismo Formation (late Pliocene to late Miocene) Miguelito Member—Brown to buff interbedded siltstone and claystone, moderately resistant, well –bedded, beds generally 2 to 4 inches thick. Locally includes beds and lenses of siliceous and dolomitic siltstone, opaline shale, porcelaneous shale, thin-bedded chert, diatomaceous shale, diatomite, friable and locally bituminous sandstone and locally conglomeratic or tuffaceous near base. (Hall and others, 1979). Edna Member—Poorly to moderately well indurated, brown to gray, fine- to medium-grained arkosic sandstone. Locally interbedded with yellow claystone. Contains 35% to 80% quartz, 5% to 15% feldspar, up to 40% silt-sized particles (Hall, 1979). Monterey Formation (late to middle Miocene) Siltstone and mudstone member—Brown to buff, thin- to thick-bedded, calcareous and porcelaneous mudstone (Sieders, 1992) and siltstone, blocky dolomitic claystone and siliceous siltstone (Hall and others, 1979). Includes lenses of dolomite, interbedded cherty shale and graded sandstone beds. Locally tuffaceous. Weathers to a light gray rock of low density locally called “chalk rock.” Dolomitic siltstone—Local dolomitic siltstone with some opaline chert. Tuffaceous mudstone and tuff member—Light gray, thin- to thick bedded, interbedded with some dark gray calcareous mudstone. Diabase and basalt (middle Miocene)—Dark olive-gray, fine- to medium grained, spheroidally weathered, diabase and basalt. Occurs as sills and dikes in the Rincon shale and as possible extrusive flows that might be interbedded locally with tuffaceous sediments in the base of the Monterey Formation. Locally exhibits weakly developed pillow structure. Rincon Shale (early Miocene and Oligocene)—Dark brown to orange brown siltstone and silty claystone, poorly- to well-bedded, weathers white to light brown. Locally contains zones of dolomite. Lithologically similar to rocks that have been assigned to the lower part of the Monterey Formation but contains fossils known to be older (Hall and Prior, 1975). Differentiated from Monterey Formation by absence of chert and pocelaneous shale. Vaqueros Sandstone (Oligocene)—Gray to brown, medium- to coarse-grained arkosic sandstone. Includes pebbly sandstone and sandy and pebbly limestone. Poorly indurated to hard, with a silty, calcareous matrix. Some beds are hard and resistant due to abundant calcite cement. Clasts are well-rounded to subrounded with a typical composition of 50% to 90% quartz, less than 10% to 30% feldspar, 5% to 35% rock fragments. Contains fossiliferous zones with oyster shells up to 17 cm. Unnamed conglomerate (Oligocene)—Massive matrix-supported, non-marine pebble, cobble and boulder conglomerate and pebbly sandstone. Clasts are subrounded to subangular and range in size from pebbles to boulders as much as 6 feet in diameter. Large clasts are mostly feldspathic biotitic sandstone derived from the Atascadero Formation. Much of the pebble and small cobble fraction is composed of volcanic porphyry and other resistant rock types likely reworked from Atascadero conglomerates. Smaller clasts include chert, mafic volcanic rock and graywacke likely derived from Franciscan mélange. These deposits were deposited in a high-energy alluvial fan environment near source areas of rapidly uplifted Mesozoic rocks. Some poorly-sorted zones with subangular boulders appear to be debris flow deposits. Mapped as the Lospe Formation by Hall and others (1975). Similar in age and type to the Sespe Formation in the southern Coast Ranges. Cambria Felsite (Oligocene) Felsite—Light gray and grayish orange crystalline felsite, commonly flow-layered with phenocrysts of quartz and plagioclase. Forms resistant ridges and volcanic plugs and domes (Hall and others 1979). Tuff—Light gray, orange and pale green tuff, lapilli tuff and tuff breccia. Locally contains reworked fragments of Franciscan blueschist, graywacke and ophiolitic serpentinite. BASEMENT COMPLEXES Franciscan Complex Mélange (Late Cretaceous)—Chaotic mixture of fragmented, fault-bounded, metamorphosed rock masses embedded in a penetratively sheared matrix of argillite and crushed metasandstone. Penetrative deformation of the matrix postdates metamorphism of enclosed rock masses. Individual rock masses range from less than a meter to kilometers in scale and include altered mafic volcanic rocks (greenstone), chert, serpentinite, high-grade blueschist, graywacke, and conglomerate. Greenstone, chert, and serpentinite blocks are probably derived from the Coast Range Ophiolite and were emplaced and interleaved in the matrix during subduction. Small pods mapped locally are designated with abbreviated labels as follows: mv – metavolcanic rock sp – serpentinite ch – chert bs – blueschist gw – graywacke Larger slabs and blocks enclosed in mélange consist of the following: Sandstone of Cambria (Late Cretaceous)—Light gray, fine- to coarse-grained, medium-bedded arkose and arkosic wacke interbedded with brown to black micaceous siltstone. Unit is more coherent and less sheared and fractured than other Franciscan units. Contains Late Cretaceous foraminifera and pollen (Graymer and others, 2014) Graywacke and Metagraywacke (Cretaceous and Jurassic?)—Brown to greenish gray, fine- to medium-grained, massive- to thin-bedded graywacke sandstone interbedded with shale and siltstone. Composed of 60% to 70% quartz; 20% to 30% feldspar, 5% biotite and 10% shale fragments embedded in a muddy matrix (Hall and Prior, 1975). Rocks are generally moderately to intensely sheared, often obscuring original stratification. This unit lacks exotic blocks characteristic of mélange. Locally includes conglomerate beds with clasts of chert, sandstone and metavolcanic rock. Chert (Cretaceous and Jurassic)—Red and green radiolarian chert associated with greenstone. Commonly veined and recrystallized, locally bleached to yellow or white. Deposited in deep oceanic setting on greenstone prior to influx of sandstone and shale. Locally interbedded with thin layers of argillite. Metavolcanic rocks (greenstone) (Cretaceous? and Jurassic)—Primarily metamorphosed basalt and diabase. Includes massive to pillowed basalt flows, breccia and tuff. Commonly deeply weathered and extensively sheared, with intermingled pods of chert. Considered to be tectonic blocks incorporated into mélange derived from the upper part of Jurassic ophiolite. Great Valley Complex - Great Valley Sequence Atascadero Formation (Late Cretaceous) Sandstone member—Light gray to dark olive gray, thin to thick-bedded turbidite sandstone with interbedded siltstone, mudstone and conglomerate. Unit structurally overlies Franciscan rocks and the Toro Formation and is internally disrupted by faulting and shearing. Sandstones typically consist of quartz (30-40%), feldspars (30-50%), volcanic and lithic debris (10-30%) and biotite (2 -10%) Hart (1976). Conglomerate member—Very thick bedded pebble, cobble and boulder conglomerate. Clast composition predominantly includes silicic volcanic rocks, quartzite and granitic rocks. Unit lacks Franciscan debris. Toro Formation (Early Cretaceous and Late Jurassic) Shale and sandstone member—Thin-bedded, greenish brown to brown micaceous shale interbedded with thin sandstone beds. Sandstone occurs rarely in beds up to 5 meters thick. Contains calcareous lenses and concretions. Buchia fragments occur locally in thin sandstone beds (Hall and Prior, 1975). Depositionally overlies chert and basalt of the Coast Range Ophiolite. Conglomerate member—Lenses of pebble and cobble conglomerate deposited as channel fills on submarine fans. Moderately well sorted. Contains well rounded clasts of chert (60 - 70%), quartzite (10 – 30%) with minor sandstone and mudstone clasts (Seiders, 1982). Limestone—Lenses of light to medium gray microcrystalline limestone. Locally contains shell fragments. Lenses are up to 10m thick (Seiders, 1982). Great Valley Complex - Coast Range Ophiolite Chert (Jurassic)—Brownish black to olive brown impure chert. Beds 2 to 15 cm thick intercalated with black, flaky, siliceous shale partings. Rock breaks into blocky, joint-bounded blocks with black manganese oxide coatings on some surface. Depositional on basaltic dike-and-sill complex. Overlain by marine shales of the Toro Formation. Basalt and Intrusive Dike-and-Sill Complex (Jurassic)—Dark brown extrusive basalt breccia and pillow lava intruded by diabase dikes and sills (oceanic crust remnant). Extensive fracturing and deep weathering typically obscures original structure of basalt. Intrusive dikes and sills are composed primarily of diabase, basalt, gabbro and quartz gabbro. Dikes and sills are locally more voluminous than host basalts and are considered to be feeders to overlying extrusive basalts. (Oceanic crust fragment of Page, 1972.) Serpentinite and Intrusive Dike-and-Sill Complex (Jurassic)—Serpentinite extensively intruded by altered diabase dikes and sills (mantle remnant). Relict minerals and textures of peridotite locally present where serpentinization is incomplete. Intrusive dikes and sills are primarily diabase typically altered to hydrous calcium aluminum silicates. Unit is in fault contact with overlying basalt dike-and-sill complex. Dikes and sills considered to be feeders to overlying extrusive basalts. Unit is tectonically underlain by Franciscan mélange. (Mantle fragment of Page, 1972.) Serpentinized Ultramafic Rocks (Jurassic)—Pervasively sheared serpentinite occurring as lenticular fault-bounded bodies in Franciscan mélange. Considered to be dismembered bodies of the Coast Range Ophiolite tectonically interleaved with mélange during subduction and entrained along faults. Locally altered to: Silica-carbonate rock—Hydrothermally altered serpentinite, composed of quartz and carbonate mineral assemblages. Relatively resistant, outcropping as craggy knobs. Qb Qd Qya 1 Qya 2 Tm Tmd Ka Kac Jbd KJtc KJtl Jch Jsp Jsd sc Tmt Qa Qls Qop Qya Qya 2 Qya 1 Tm Tdb Jch Tpe Ka QUATERNARY TERTIARY CRETACEOUS JURASSIC Holocene Pleistocene Pliocene Miocene Oligocene Tpm Tcg Great Valley Sequence Tv CORRELATION OF MAP UNITS Kac Great Valley Complex Qd Qb ? Tmt Tr Tft Tf Jbd KJt KJtc KJtl Jsd Coast Range Ophiolite Tmd Kfs Franciscan Complex Kfm ch mv sp KJfc bs gw KJfg KJfv BASEMENT COMPLEXES Jsp sc
