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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 CAYUCOS 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 CAYUCOS 7.5' QUADRANGLE SAN LUIS OBISPO COUNTY, CALIFORNIA VERSION 1.0 Mapping and Digital Preparation By Marc Delattre 2016 35°30' 120°52’30'' 35°24' 120°52'30” 35°30' Coordinate System: Universal Transverse Mercator, Zone 10N North American Datum 1927. Topographic base from U.S. Geological Survey Cayucos 7.5-minute Quadrangle, 1965 (Revised 1994). Shaded relief image derived from USGS 1/3 arc-second National Elevation Dataset (NED). 121°02'30” 121°02'30” 35°24' Professional Licenses and Certifications: M.P. Delattre - PG No. 5230, CEG No. 1819 Preliminary Geologic Map available from: http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm 121°00' This geologic map was entirely funded by CGS. The work was performed in coordination with mapping of the adjacent Morro Bay North 7 1/2’ quadrangle, which was funded in part by the USGS National Cooperative Geologic Mapping Program, Statemap Award no. G15AS00006 121°00' (P (P (P (Pas as as a o Robl les es) ) ) (Paso Robles) - Adjacent 30’ x 60’ quadrangles (T ( (T (T T aft) (S (S (S (S (S S ( (S San an an an an n an nt ta t t ta ta M M M M Maria) 135 58 41 229 227 166 46 101 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 LOPE PE PE PE PE P P PE PE PE PE PE PE Z 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 TA TAR R R R A A A AR R R R R SP SP SP SP SP SP SP S SP SP SP SP SP SP SP SP SPRI RI RI RI R R R R NG NG NG NG NG R RI RI RI RI RI R RI RIDG 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 L WE WE WE WE WE WE WELL LL LL LL LL L 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 M MA MA MA MA MA ACH 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 BR BRA A A A A A A R 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 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 M MT MT MT MT MT MT MTN N N N N N N H H H H H H H HU HU HU HU HU HU HUAS AS AS AS AS AS ASNA NA NA NA NA NA NA PE PE PE PE PE PE PE PE PEAK AK AK AK A AK AK AK AK AK AK AK AK K K K NIPOMO OCEANO CH CH CH CH CH CH C CH CH CH CH CH CH HIM IM IM IM IM IM IM M M M M MNE NE NE NE NE N N NE NE N N N Y 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 YON ON O ON ON ON ON O O Y Y Y Y Y YON ON ON O O ON ON O ON ON SANTA MARGARITA TA SA SA SA SA SA SA A A A ANT NT NT NT N N N N N N N A A A A T T T A A A A RGA MA MA MA MA MA MA A MA A MA MA M MA MA MARG RG RG RG RG R R R R RGA A A A RG RG RG RG RGAR AR AR AR AR RIT IT IT IT IT IT A A A A A LA LA LA LA LA LA AKE KE KE KE KE K WI WI WI WI WI W WI WILS LS LS LS LS LS LSON ON ON ON ON ON N N N N N N CO CO CO C C C CO C RN RN RN RN RN RN RN RN RN RN NER ER ER ER ER E C CA CA CA CA CA CA CA AMA MA MA MA MA MA MA MA TT TT TT TT TT TT TT TT A A A A T T T T A A A A TTA 5 8 RA RA RA RA ANC NC NC NC A ANC NC NC NC CH H H H ZO PO PO PO PO PO PO POZO ZO ZO ZO ZO ZO ZO ZO ZO ZO ZO ZO O UM SU SU SU SU UM M M M U U U UMM MM MM MM MMIT IT IT IT T LA LA LA LA P P P P P P P AN AN AN AN AN AN ANZA ZA ZA ZA ZA ZA Z ZA ZA ZA ZA ZA ZA A RA RA RA RA A A ANC NC NC NC A A A ANC NC NC NC CH H H H H PA LA LA LA LA LA LA LA P P P P P P P A A A A A P P P P P AN AN AN AN AN AN NZA ZA ZA Z ZA ZA Z FO CA CA CA CA CA CA CALI LI LI LI LIFO FO F FO FO FO FO FO FO O ORN RN RN RN RN RN RNIA IA IA IA IA IA I V V V V V VA VA VA VALL LL LL LL L L LEY EY EY EY EY EY E LA LA LA LA P P P AN AN ANZA ZA Z ZA ZA A 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 ’ d d d dra ra ra rang ng ng ng ng n le le le le le e n n Lu Luis is O Obi bisp spo o n Luis Obispo 30 30’x ’x ’x60 60 60’ ’ qu quad ad 30’x60’ quad n d REFERENCES Chapman, A.D., Jacobson, C.E., Ernst, W.G., Grove, M., Dumitru, T., Hourigan, J., and Ducea, M.N., 2016, Assembling the world’s type shallow subduction complex: Detrital zircon geochronologic constraints on the origin of the Nacimiento block, central California Coast Ranges: Geosphere, v. 12, no. 2, p. 1-25, doi:10.1130/GES01257.1. 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. Ernst, W.G. and Hall, C.A., 1974, Geology and petrology of the Cambria felsite, a new Oligocene Formation, west-central California Coast Ranges: Geological Society of America, Bulletin v.85, n.4, scale 1:24,000 Graymer, R.W., Langenheim, V.E., Roberts, M.A., and McDougall, Kristin, 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 Investigations Map SIM-3287, scale 1:100,00. 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. 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. McClean, H., 1994, Geologic Map of the Lopez Mountain Quadrangle, San Luis Obispo, California; U.S. Geological Survey Geological Quadrangle Map GQ-1723. 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. 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 ? 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. Anticlinal axis - Solid where accurately located; dashed where approximately located; dotted where concealed. Arrow shows plunge direction. Strike and dip of bedding plane. Vertical bedding Landslide - Arrows indicate principal direction of movement. MAP SYMBOLS ? Qa Qls af Qya Qoa Tdb DESCRIPTION OF MAP UNITS SURFICIAL UNITS Artificial fill (Historic)—Mapped locally, primarily larger highway fills and embankment dams for lakes. Beach and dune deposits (late Holocene)—Unconsolidated, mostly fine- and medium-grained sand accumulated along the coastline; includes scattered cobbles. 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, and 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; also deeper rock slides consisting of relatively intact bedrock displaced along rotational or translational slip surfaces. 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. Young alluvial fan deposits (Holocene to late Pleistocene)—Unconsolidated gravel, sand, silt, and clay-bearing alluvium deposited in characteristic fan-shaped morphology on terraces and floodplains at the mouths of steep drainages with fan. Old alluvial flood-plain deposits (late Pleistocene)—Fluvial sediments preserved above active flood plains and channels. Consist of weakly-consolidated silty sand and sandy gravel with cobbles. Terrace surfaces preserved along drainages are slightly dissected and capped by moderately- to well-developed pedogenic soils. Old paralic deposits (late Pleistocene)—Marine terrace deposits consisting of beach and nearshore sands and gravels, commonly containing fossils and shell fragments; nearly everywhere covered by colluvium and alluvial fan deposits included as part of map unit. These deposits rest on an emergent wave-cut platform preserved by regional uplift. At two locations northwest of the town of Cayucos the wave-cut platform has been dated at approximately 120 ka (Hanson and others, 1994). TERTIARY ROCKS 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. 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). Cambria Felsite (Oligocene)—Light gray and grayish orange crystalline felsite, commonly flow-layered with phenocrysts of quartz and plagioclase. Includes some soft, white tuff. Forms resistant ridges and volcanic plug-like masses (Hall and others,1979). 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 cg – conglomerate Larger slabs and blocks enclosed in mélange consist of the following: Sandstone of Cambria (Late Cretaceous)—Light gray, orange-brown weathering, medium- to thick-bedded, fine- to coarse-grained arkose and arkosic wacke. In places interbedded with brown to black siltstone with locally abundant biotite and carbonaceous debris. Unit is more coherent and less sheared and fractured than other Franciscan units. Contains Late Cretaceous foraminifera and pollen (Graymer and others, 2014). This unit has also yielded detrital zircons of about 80–90 Ma (Chapman and others, 2016). 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. Crops out as fault-bounded slabs and blocks in mélange. 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. Locally includes conglomerate beds with clasts of chert, sandstone and metavolcanic rock. Exotic blocks characteristic of mélange are absent or rare. Mafic metavolcanic rocks (greenstone) (Cretaceous? and Jurassic)—Primarily metamorphosed basalt and diabase. Includes massive to pillowed basalt flows, breccia, and minor tuff. Typically deeply weathered and extensively sheared. Commonly associated with pods of contorted ribbon chert and slivers of chert too small to distinguish at map scale. Considered to be tectonic blocks incorporated into mélange derived from the upper part of Jurassic ophiolite. Chert (Cretaceous and Jurassic)—Red and green radiolarian chert and metachert associated with mafic volcanic rocks. Commonly veined and recrystallized, locally bleached to yellow or white. Deposited in deep oceanic setting prior. Locally interbedded with thin layers of argillite. Great Valley Complex - Coast Range Ophiolite 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 Qyf Qop Kfm Kfs KJfg KJfc KJfv Jsp sc Tr Tf Qa Qb Qls Qya Qoa QUATERNARY TERTIARY Holocene Pleistocene Pliocene Miocene Oligocene CORRELATION OF MAP UNITS Jsp BASEMENT COMPLEXES Kfs ? 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1.5
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2Thousand Feet
Kilometers
Miles
Scale 1:24,000
Contour Interval 40 feetSupplementary Contour Interval 20 feet
National Geodetic Vertical Datum of 1929
APPROXIMATE MEANDECLINATION, 2016
12.9°
TRU
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STATE OF CALIFORNIA – EDMUND G. BROWN JR., GOVERNORNATURAL RESOURCES AGENCY – JOHN LAIRD, SECRETARY FOR NATURAL RESOURCES
DEPARTMENT OF CONSERVATION – DAVID BUNN, DIRECTOR CALIFORNIA GEOLOGICAL SURVEYJOHN G. PARRISH, Ph.D., STATE GEOLOGIST PRELIMINARY GEOLOGIC MAP OF THE CAYUCOS 7.5’ QUADRANGLE, CALIFORNIA
Copyright © 2016 by the California Department of Conservation,California Geological Survey. All rights reserved. No part ofthis publication may be reproduced without written consent of theCalifornia Geological Survey.
"The Department of Conservation makes no warranties as to thesuitability of this product for any given purpose."
PRELIMINARY GEOLOGIC MAP OF THE CAYUCOS 7.5' QUADRANGLESAN LUIS OBISPO COUNTY, CALIFORNIA
VERSION 1.0Mapping and Digital Preparation
By Marc Delattre
2016
35°30'120°52’30''
35°24'120°52'30”
35°30'
Coordinate System:Universal Transverse Mercator, Zone 10NNorth American Datum 1927.
Topographic base from U.S. Geological SurveyCayucos 7.5-minute Quadrangle, 1965 (Revised 1994).Shaded relief image derived from USGS 1/3 arc-second National Elevation Dataset (NED).
121°02'30”
121°02'30”35°24'
Professional Licenses and Certifications: M.P. Delattre - PG No. 5230, CEG No. 1819
Preliminary Geologic Map available from:http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm121°00'
This geologic map was entirely funded by CGS. The work was performed in coordination with mapping of the adjacent Morro Bay North 7 1/2’ quadrangle, which was funded in part by the USGS National Cooperative Geologic Mapping Program, Statemap Award no. G15AS00006
121°00'
(P(P(P(Pasasasa o Roblleses)))
(Paso Robles) - Adjacent 30’ x 60’ quadrangles
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41229
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Mapping completed under STATEMAP
Previous projects since 2008
FY 2015-16
SAN LUISOBISPO
Other new mapping by CGSFY 2015-16
121°0’0” 120°30’0” 120°0’0”
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REFERENCESChapman, A.D., Jacobson, C.E., Ernst, W.G., Grove, M., Dumitru, T., Hourigan, J., and Ducea, M.N.,
2016, Assembling the world’s type shallow subduction complex: Detrital zircon geochronologic constraints on the origin of the Nacimiento block, central California Coast Ranges: Geosphere, v. 12, no. 2, p. 1-25, doi:10.1130/GES01257.1.
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.
Ernst, W.G. and Hall, C.A., 1974, Geology and petrology of the Cambria felsite, a new Oligocene Formation, west-central California Coast Ranges: Geological Society of America, Bulletin v.85, n.4, scale 1:24,000
Graymer, R.W., Langenheim, V.E., Roberts, M.A., and McDougall, Kristin, 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 Investigations Map SIM-3287, scale 1:100,00.
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.
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.
McClean, H., 1994, Geologic Map of the Lopez Mountain Quadrangle, San Luis Obispo, California; U.S. Geological Survey Geological Quadrangle Map GQ-1723.
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.
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
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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.
Anticlinal axis - Solid where accurately located; dashed where approximately located; dotted where concealed. Arrow shows plunge direction.
Strike and dip of bedding plane.
Vertical bedding
Landslide - Arrows indicate principal direction of movement.
MAP SYMBOLS
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Qa
Qls
af
Qya
Qoa
Tdb
DESCRIPTION OF MAP UNITS
SURFICIAL UNITS
Artificial fill (Historic)—Mapped locally, primarily larger highway fills and embankment dams for lakes.
Beach and dune deposits (late Holocene)—Unconsolidated, mostly fine- and medium-grained sand accumulated along the coastline; includes scattered cobbles.
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, and 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; also deeper rock slides consisting of relatively intact bedrock displaced along rotational or translational slip surfaces.
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.
Young alluvial fan deposits (Holocene to late Pleistocene)—Unconsolidated gravel, sand, silt, and clay-bearing alluvium deposited in characteristic fan-shaped morphology on terraces and floodplains at the mouths of steep drainages with fan.
Old alluvial flood-plain deposits (late Pleistocene)—Fluvial sediments preserved above active flood plains and channels. Consist of weakly-consolidated silty sand and sandy gravel with cobbles. Terrace surfaces preserved along drainages are slightly dissected and capped by moderately- to well-developed pedogenic soils.
Old paralic deposits (late Pleistocene)—Marine terrace deposits consisting of beach and nearshore sands and gravels, commonly containing fossils and shell fragments; nearly everywhere covered by colluvium and alluvial fan deposits included as part of map unit. These deposits rest on an emergent wave-cut platform preserved by regional uplift. At two locations northwest of the town of Cayucos the wave-cut platform has been dated at approximately 120 ka (Hanson and others, 1994).
TERTIARY ROCKS
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. 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).
Cambria Felsite (Oligocene)—Light gray and grayish orange crystalline felsite, commonly flow-layered with phenocrysts of quartz and plagioclase. Includes some soft, white tuff. Forms resistant ridges and volcanic plug-like masses (Hall and others,1979).
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 rocksp – serpentinitech – chertbs – blueschistgw – graywackecg – conglomerate
Larger slabs and blocks enclosed in mélange consist of the following:Sandstone of Cambria (Late Cretaceous)—Light gray, orange-brown weathering, medium- to
thick-bedded, fine- to coarse-grained arkose and arkosic wacke. In places interbedded with brown to black siltstone with locally abundant biotite and carbonaceous debris. Unit is more coherent and less sheared and fractured than other Franciscan units. Contains Late Cretaceous foraminifera and pollen (Graymer and others, 2014). This unit has also yielded detrital zircons of about 80–90 Ma (Chapman and others, 2016).
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. Crops out as fault-bounded slabs and blocks in mélange. 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. Locally includes conglomerate beds with clasts of chert, sandstone and metavolcanic rock. Exotic blocks characteristic of mélange are absent or rare.
Mafic metavolcanic rocks (greenstone) (Cretaceous? and Jurassic)—Primarily metamorphosed basalt and diabase. Includes massive to pillowed basalt flows, breccia, and minor tuff. Typically deeply weathered and extensively sheared. Commonly associated with pods of contorted ribbon chert and slivers of chert too small to distinguish at map scale. Considered to be tectonic blocks incorporated into mélange derived from the upper part of Jurassic ophiolite.
Chert (Cretaceous and Jurassic)—Red and green radiolarian chert and metachert associated with mafic volcanic rocks. Commonly veined and recrystallized, locally bleached to yellow or white. Deposited in deep oceanic setting prior. Locally interbedded with thin layers of argillite.
Great Valley Complex - Coast Range Ophiolite
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.
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Qyf
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Kfm
Kfs
KJfg
KJfc
KJfv
Jsp
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QaQb
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TERTIARY
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
CORRELATION OF MAP UNITS
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BASEMENT COMPLEXES
Kfs
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Franciscan Complex
Great Valley Complex
Kfmch
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Coast Range Ophiolite
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Qyf
Tdb
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CRETACEOUS
JURASSIC
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