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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

Offshore Geology and Geomorphology of Point San Luis 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

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

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

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

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120°40'

120°40'

120°45'

120°45'

120°50'

120°50'

120°55'

120°55'

35°15'

35°15'

35°10'

35°10'

35°5'

35°5'

San Luis

Obispo

Pismo Beach

Oceano

Diablo Canyon

Power Plant

San Luis Bay

Point 

Buchon

Point 

San Luis

Shell Beach

LOS OSOS FAULT

EDNA FAULT

HOSGRI FAULT

SHORELINE FAULT

HOSGRI FAULT

SHORELINE FAULT

POINT BUCHON FAULT

SAN MIGUELITO FAULT

SAN LUIS BAY FAULT

WILMAR AVENUE

FAULT

OCEANO FAULT

0 5 10

OF

CF

HF

CF

RF

LOF

EF

SF

SMF

WAF

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 5 AND 6 (POINT SAN LUIS), OUTLINED IN RED, IN RELATION TO AREAS OF SHEETS 1 AND 

2 (SAN SIMEON) AND 3 AND 4 (ESTERO BAY). 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

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/Tm indicates that thin sheet of Qms overlies 

Tm)] 

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

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

Marine rill (Holocene)—Inferred to be sand, coarse sand, and possibly gravel; forms fields of narrow, 

elongate, and shallow channels, or rills, cut into shelf. Narrow channels are characterized by high 

backscatter and are, therefore, inferred to be filled with coarse sand or gravel. These features may be 

related to “sorted bedforms” (Trembanis and Hume, 2011) because they often are found adjacent to, or 

surrounded by, areas of sorted bedforms

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

siltstone, shale, locally thin-bedded chert, and diatomaceous shale

Monterey Formation, undivided (Miocene)—Diatomaceous, porcelaneous, and opaline shale; tuffaceous 

siltstone; and claystone. Stippled areas (composite unit Qms/Tm) indicate where thin sheets of Qms

overlie unit 

Shale subunit (late and middle Miocene)—Opaline or cherty shale; mapped only in nearshore directly 

adjacent to onland outcrops (Hall, 1973a) 

Obispo Formation, undivided (Miocene)—Includes crystal-bearing vitric tuff, tuffaceous siltstone and 

claystone, and resistant zeolitized tuff. Stippled areas (composite unit Qms/To) indicate where thin sheets 

of Qms overlie unit

Diabase and basalt subunit (Miocene)—Diabase and basalt 

Resistant tuff subunit (Miocene)—Zeolitized, resistant tuff 

Vitric tuff subunit (Miocene)—Crystal-bearing vitric tuff 

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

and siltstone; mapped in Point San Luis area, in accordance with adjacent onland mapping (Hall, 1973a). 

Correlated with the unnamed sandstone and interbedded shale unit (Ksl), mapped in San Simeon and 

Morro Bay areas (see sheets 1, 3). Stippled areas (composite unit Qms/Kslc) 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, queried where existence is 

questionable

Antiform

Synform

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

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., 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.

Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand—

Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203–214.

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/.

Qmss

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To

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af

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Qmr

Qmsh

CORRELATION OF MAP UNITS

Qms Qmsf Qmss Qmsl

Tod

Tot

Tor

Jo

Tmsch

af

Tmpm

Tm To

Kslc

Pliocene

Miocene

Holocene

TERTIARY

QUATERNARY

Cretaceous

MESOZOIC

Jurassic

Qmsh Qmc Qmp Qmr

KJf

Scientific Investigations Map 3327

Sheet 5 of 6

Pamphlet accompanies map