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This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters 

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proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3327 or http://pubs.usgs.gov/sim/3327/

Suggested Citation: Watt, J.T., Johnson, S.Y., Hartwell, S.R., and Roberts, M., 2015, Offshore geology and geomorphology from Point 

Piedras Blancas to Pismo Beach, San Luis Obispo County, California: U.S. Geological Survey Scientific Investigations Map 3327, 

pamphlet 6 p., 6 sheets, scale 1:35,000, http://dx.doi.org/10.3133/sim3327.

ISSN 2329-132X(online)

http://dx.doi.org/10.3133/sim3327

U.S. Department of the Interior

U.S. Geological Survey

SCALE 1:35 000

1 1/2 0 1 MILE

ONE MILE = 0.869 NAUTICAL MILES

BATHYMETRIC CONTOUR INTERVAL 10 METERS

1 .5 0 1 KILOMETER

Ksl

Ksl

Jo?

TKu

Ksl

TKu

Tus

Tus

Qmsf

Ksl

af

Ksl

KJf

Qmsf

KJf

af

KJf

Ksl

Tus

Qms

Qms

Qmsf

Qmss

Qmss

Tus

Qmsf

Tmpm

Qms

Ksl

KJf

TKu

Qmsf

Tmpm

Qms

Qmss Ksl

TKu

KJf

KJf

Qms/Ksl

Qmsc

Qms/Ksl

Qmss

Qmss

KJf

Qms/KJf

Qmss

Ksl

Qms

Tus

Qmc

Tus

Qmss

Qms

Ksl

Tus

Qms

Qmss

KJf

Qmc

Ksl

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Qms

Qmss

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KJf

Ksl

TKu

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TKu

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Tus

Qms/Ksl

Qmss

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Tus

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KJf

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Ksl

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Qmss

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af

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Ksl

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Tmpm

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Tmpm

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af

TKu

Tus

Tus

Tus

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Qms

KJf

Tus

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Tus

TKu

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Qms

Jo?

Ksl

KJf

Qms

KJf

TKu

Qmss

Qmss

TKu

Tmpm

Qmss

Tmpm

Qms/KJf

Qmsf

Qmss

Qmss

Qms/Tmpm

Qms/KJf

Qmss

Qmss

Qmss

Qmss

Qmc

Qmss

Qms/Ksl

Qms/Ksl

Tus

Qmss

Qms/Tmpm

TKu

TKu

Qmsl

Qmsl

Qmsl

Qmsf

Qms/Tus

Qmsl

Qmsl

Qmsl

Qls

Qls

Qmsf

Tmpm

120°50'

120°50'

120°55'

120°55'

121°

121°

121°5'

121°5'

121°10'

121°10'

35°25'

35°25'

35°20'

35°20'

Cayucos

Morro Bay

Point Estero

Estero Bay

LOS OSOS FAULT

CAMBRIA FAULT

OCEANIC FAULT

HOSGRI FAULT

LOS OSOS FAULT ZONE

20

40

60

80

100

120

140

160

180

200

LOS OSOS FAULT (north strand)

LOS OSOS FAULT (south strand)

LOS OSOS FAULT (north strand)

LOS OSOS FAULT (central strand)

Offshore Geology and Geomorphology of Estero Bay Map Area

Offshore Geology and Geomorphology from Point Piedras Blancas to Pismo Beach, 

San Luis Obispo County, California

By

Janet T. Watt, Samuel Y. Johnson, Stephen R. Hartwell, and Michelle Roberts

2015

CALIF.

MAP LOCATION

13°

APPROXIMATE MEAN

DECLINATION, 2015

MAGNETIC 

NORTH

TRUE NORTH

Offshore geology and geomorphology mapped by Janet T. 

Watt and Samuel Y. Johnson, 2010-2013. Onshore faults 

from Quaternary fault and fold database (U.S. Geological 

Survey and California Geological Survey, 2010) 

GIS database and digital cartography by Janet T. Watt, 

Stephen R. Hartwell, and Theresa Fregoso

Edited by Taryn A. Lindquist

Manuscript approved for publication April 14, 2015

Bathymetric shaded-relief imagery (10X vertical exaggeration) from gridded multibeam bathymetry 

acquired, processed, archived, and distributed by California State University, Monterey Bay, Seafloor 

Mapping Lab (CSUMB) and by U.S. Geological Survey (Hartwell and others, 2013)

Bathymetric contours derived from gridded multibeam bathymetry (CSUMB), 1/3 arc-second NOAA 

Tsunami Inundation DEM (Friday and others, 2011), and regional 3 arc-second NOAA DEM (National 

Oceanic and Atmospheric Administration National Geophysical Data Center, 2011)

Elevation data from U.S. Geological Survey National Elevation Database (1/3 arc-second); sun 

illumination from northwest (315°) at 45° above horizon

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

0 5 10

OF

CF

HF

CF

RF

LOF

EF

SF

SMF

OCF

LOF

HF

PPB

MB

PB

PBU

SAN SIMEON

POINT SAN LUIS

ESTERO BAY

121 ̊15’ 121 ̊ 120 ̊45’

35 ̊30’ 35 ̊15’

MILES

SSF

SS

CM

PE

CA

SLO

DC

PSL

SLF

Estero

Bay

San Luis

Bay

PBF

KILOMETERS O

SB

INDEX MAP SHOWING AREAS OF SHEETS 3 AND 4 (ESTERO BAY), OUTLINED IN RED, IN RELATION TO AREAS OF SHEETS 1 AND 2 

(SAN SIMEON) AND 5 AND 6 (POINT SAN LUIS). FAULT ABBREVIATIONS: CF, CAMBRIA FAULT; EF, EDNA FAULT; HF, HOSGRI FAULT; 

LOF, LOS OSOS FAULT ZONE; OCF, OCEANO FAULT; OF, OCEANIC FAULT; PBF, POINT BUCHON FAULT; RF, RINCONADA FAULT; SF, 

SHORELINE FAULT; SLF, SAN LUIS BAY FAULT; SMF, SAN MIGUELITO FAULT; SSF, SAN SIMEON FAULT; WAF, WILMAR AVENUE FAULT. 

OTHER ABBREVIATIONS: CA, CAYUCOS; CM, CAMBRIA; DC, DIABLO CANYON POWER PLANT; MB, MORRO BAY; O, OCEANO; PB, 

PISMO BEACH; PBU, POINT BUCHON; PE, POINT ESTERO; PPB, POINT PIEDRAS BLANCAS; PSL, POINT SAN LUIS; SB, SHELL BEACH; 

SLO, SAN LUIS OBISPO; SS, SAN SIMEON

0 5 10

WAF

Qmss

Qmsl

Qls

Qms

Qmsc

Qmsf

Tmpm

Jo

Tus

TKu

Ksl

KJf

af

Qmc

Qmp

Qmsh

DESCRIPTION OF MAP UNITS

[Note that composite units (gray-stippled areas) are designated on map by composite label indicating both overlying 

sediment cover and lower (older) unit, separated by slash (for example, Qms/TKu indicates that thin sheet of Qms

overlies TKu)] 

Artificial fill (Holocene)—Rock, sand, and mud; placed and (or) dredged. Also includes seafloor significantly 

modified by human activity

Marine nearshore and shelf deposits (Holocene)—Mostly sand; ripples common

Coarse-grained marine nearshore and shelf deposits (Holocene)—Predominantly coarse sand, gravel, and 

cobbles. Recognized primarily on basis of high backscatter and flat relief

Fine-grained marine nearshore and shelf deposits (Holocene)—Predominantly mud to muddy sand

Marine shelf sorted bedforms (Holocene)—Inferred to be coarse sand and possibly gravel; found as single 

depressions or in fields of depressions interspersed with elevated shelf sediments (unit Qms). Although 

no direct camera observations of these bedforms were made in map area, their composition is inferred 

from similar features directly observed elsewhere on California shelf

Marine shelf hummocky deposits (Holocene)—Sand and mud; forms hummocky surface relief on shelf over 

large areas (4 to 8 km2) 

Marine slope deposits (Holocene)—Sand and mud; found offshore of shelf break (more than about 80 m 

deep) on seaward-dipping (6°–8°) surface

Marine channel deposits (Holocene)—Predominantly coarse sand; characterized by high backscatter

Marine pockmarks (Holocene)—Sand and mud; forms pockmarks on outer shelf and slope. Pockmarks are 

solitary, circular features that are found along trace of Hosgri Fault and, thus, may be associated with 

fluid venting along fault zone

Landslide deposits (Holocene and latest Pleistocene)—May represent various forms of submarine sediment 

instabilities, including slumps, slides, and collapse depressions. Characterized by hummocky bathymetry 

and headscarps incised into shelf (unit Qmsf) or slope (unit Qmsl) deposits

Pismo Formation, Miguelito Member (Pliocene and late Miocene)—Predominantly brown claystone and 

siltstone, shale, locally thin-bedded chert, and diatomaceous shale. Stippled areas (composite unit 

Qms/Tmpm) indicate where thin sheets of Qms overlie unit

Sedimentary bedrock (Tertiary)—Includes sedimentary rocks from the Monterey and Pismo Formations; 

distinguished on basis of bedding character in shallow seismic-reflection data and (or) multibeam 

imagery. Stippled areas (composite unit Qms/Tus) indicate where thin sheets of Qms overlie unit 

Bedrock, undivided (Tertiary and Cretaceous)—May include rocks of any of Tertiary- to Jurassic-age units 

mapped herein, as well as of Oligocene dacite and dacite flow facies associated with Islay Hill–Morro 

Rock complex (Hall, 1973a). Stippled areas (composite unit Qms/TKu) indicate where thin sheets of 

Qms overlie unit

Unnamed sandstone and interbedded shale (Late Cretaceous)—Sandstone and interbedded shale and 

siltstone; mapped in Sam Simeon and Morro Bay areas, in accordance with adjacent onland mapping 

(Hall, 1973a, 1974). Correlated with the unnamed sandstone and interbedded claystone unit (Kslc), 

mapped in Point San Luis area (see sheet 5). Stippled areas (composite unit Qms/Ksl) indicate where 

thin sheets of Qms overlie unit

Franciscan Complex (Cretaceous and Jurassic)—Includes fine- to coarse-grained sandstone, siltstone, and 

some claystone, as well as mélange. Mélange is mainly composed of sheared claystone that contains 

exotic clasts of conglomerate, blueschist, schist, greenstone, chert, graywacke, and shale. Stippled areas 

(composite unit Qms/KJf) indicate where thin sheets of Qms overlie unit

Coast Range ophiolite (Jurassic)—Includes diabase, basalt, microdiorite, dikes and sills, diorite, and 

serpentinite. Ophiolite sequences mapped onland at Point Piedras Blancas and Point San Luis (Hall, 

1973a, 1976). Serpentinite, which often is faulted and sheared within the Franciscan Complex, is found in 

lenses along fault zones. Stippled areas (composite unit Qms/Jo) indicate where thin sheets of Qms

overlie unit

EXPLANATION OF MAP SYMBOLS

Contact—Approximately located

Fault (offshore)—Solid where location is certain, dashed where location is inferred, dotted where location is 

concealed, queried where existence is questionable

Fault (onshore)—Solid where location is certain, long-dashed where location is approximate, short-dashed 

where location is inferred

Folds—Solid where location is certain, dotted where location is concealed

Antiform

Synform

Headscarp of submarine landslide—Sharp, distinct scarp at head of landslide; in places, forms contact 

between landslide deposits (Qls) and other units. Hachures point downscarp

Shelf break—Boundary between continental shelf and upper slope, mapped on basis of distinct break in slope 

that is visible in multibeam bathymetry or on seismic-reflection profiles. Forms contact between shelf 

(Qmsf) and slope (Qmsl) deposits. Coincident with submarine landslide scarps offshore of Point Estero

Slope break—Break in slope along top of latest Pleistocene nearshore bar

Boundary of multibeam-bathymetry survey 

Area of “no data”—Areas not mapped owing to insufficient high-resolution seafloor mapping data

REFERENCES CITED

Friday, D.Z., Taylor, L.A., Eakins, B.W., Carignan, K.S., Grothe, P.R., Lim, E., and Love, M.R., 2011, Digital elevation 

models of Port San Luis, California—Procedures, data sources, and analysis: National Oceanic and Atmospheric 

Administration National Geophysical Data Center, Coastal DEMs, accessed December 2011, at 

http://www.ngdc.noaa.gov/mgg/coastal/coastal.html.

Hall, C.A., 1973a, Geologic map of the Morro Bay South and Port San Luis quadrangles, San Luis Obispo County, 

California: U.S. Geological Survey Miscellaneous Field Studies Map MF–511, scale 1:24,000. 

Hall, C.A., 1974, Geologic map of the Cambria region, San Luis Obispo County, California: U.S. Geological Survey 

Miscellaneous Field Studies Map MF–599, scale 1:24,000.

Hall, C.A., 1976, Geologic map of the San Simeon–Piedras Blancas region, San Luis Obispo County, California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF–784, scale 1:24,000.

Hartwell, S.R., Finlayson, D.P., Dartnell, P., and Johnson, S.Y., 2013, Bathymetry and acoustic backscatter—Estero Bay, 

California: U.S. Geological Survey Open-File Report 2013–1225, available at http://pubs.usgs.gov/of/2013/1225/.

National Oceanic and Atmospheric Administration National Geophysical Data Center, 2011, U.S. coastal relief model, 

vol. 6—Southern California: National Oceanic and Atmospheric Administration National Geophysical Data Center, 

U.S. Coastal Relief Model, accessed December 2011, at http://www.ngdc.noaa.gov/mgg/coastal/grddas06/

grddas06.htm.

U.S. Geological Survey and California Geological Survey, 2010, Quaternary fault and fold database of the United States: 

U.S. Geological Survey database, accessed January 3, 2012, at http://earthquake.usgs.gov/hazards/qfaults/.

Pliocene

Miocene

Pleistocene

TERTIARY

Cretaceous

Jurassic

MESOZOIC

CORRELATION OF MAP UNITS

Qms Qmsf Qmss Qmsl Qls Holocene

QUATERNARY

af Qmsc Qmsh Qmc Qmp

Oligocene

Jo

Tmpm

Tus

TKu

Ksl

KJf

Scientific Investigations Map 3327

Sheet 3 of 6

Pamphlet accompanies map