Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government

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

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://pubs.usgs.gov/sim/3254/

Suggested Citation: Johnson, S.Y., Ritchie, A.C., Seitz, G.G., and Gutierrez, C.I., 2013, Offshore and onshore geology and geomorphology, Offshore of Ventura map area, California, sheet 

10 in Johnson, S.Y., Dartnell, P., Cochrane, G.R., Golden, N.E., Phillips, E.L., Ritchie, A.C., Kvitek, R.G., Greene, H.G., Krigsman, L.M., Endris, C.A., Seitz, G.G., Gutierrez, C.I., Sliter, R.W., 

Erdey, M.D., Wong, F.L., Yoklavich, M.M., Draut, A.E., and Hart, P.E. (S.Y. Johnson and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Ventura, California: U.S. 

Geological Survey Scientific Investigations Map 3254, pamphlet 42 p., 11 sheets, scale 1:24,000, available at http://pubs.usgs.gov/sim/3254/.

Qyf

Qt

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Qoa2

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Tps

Qmsc

Qms

Qmsf

Qmss

Tp

pd

af

DISCUSSION

Marine geology and geomorphology was mapped in the Offshore of Ventura map area from approximate Mean High Water 

(MHW) to the 3-nautical-mile limit of California’s State Waters. MHW is defined at an elevation of 1.33 m above the North 

American Vertical Datum of 1988 (NAVD 88) (Weber and others, 2005). Offshore geologic units were delineated on the basis of 

integrated analyses of adjacent onshore geology with multibeam bathymetry and backscatter imagery (sheets 1, 2, 3), seafloorsediment and rock samples (Reid and others, 2006), digital camera and video imagery (sheet 6), and high-resolution seismicreflection profiles (sheet 8). 

The onshore geology was compiled from Dibblee (1986), Tan and others (2003a,b), and Tan and Clahan (2004). Unit ages, 

which are from Tan and others (2003a,b) and Minor and others (2009), reflect local stratigraphic relations.

The offshore part of the map area largely consists of a relatively shallow (less than about 40 m deep), gently offshoredipping (less than 1°) shelf underlain by recent deltaic deposits of the Santa Clara and Ventura Rivers. The mean annual 

sediment load of these two rivers exceeds 3.25 kilotons per year (Warrick and Farnsworth, 2009a), and the area is largely part of 

an extensive Quaternary deltaic depocenter (Dahlen, 1992; Slater and others, 2002; Sommerfield and others, 2009). Shelf 

deposits are primarily sand (unit Qms) at depths less than about 25 m and, at depths greater than about 25 m, are more 

fine-grained sediment (very fine sand, silt, and clay) of unit Qmsf. The boundary between units Qms and Qmsf is based on 

observations and extrapolation from sediment sampling (see, for example, Reid and others, 2006) and camera ground-truth 

surveying (see sheet 6). Given that this is an area of abundant sediment supply and active sediment transport (Barnard and 

others, 2009; Warrick and Farnsworth, 2009a), it is important to note that the boundary between units Qms and Qmsf should be 

considered transitional and approximate and is expected to shift as a result of seasonal- to annual- to decadal-scale cycles in 

wave climate, sediment supply, and sediment transport.

Offshore of the mouth of the Ventura River, at water depths of between 20 and 30 m, the sandy shelf (unit Qms) includes 

an area of irregular arcuate depressions floored by coarser sediment (coarse sand and possibly gravel; unit Qmss). Such features 

have been referred to as “rippled-scour depressions” (see, for example, Cacchione and others, 1984) or “sorted bedforms” (see, 

for example, Goff and others, 2005; Trembanis and Hume, 2011). Although the general area in which unit Qmss depressions are 

found is not likely to change substantially, the boundaries of the unit(s), as well as the locations of individual depressions and 

their intervening flat sand sheets, likely are ephemeral, changing during significant storm events.

Coarser grained deposits (unit Qmsc), which are recognized on the basis of high backscatter (sheet 3), camera observations 

(sheet 6), and sampling (Reid and others, 2006; Barnard and others, 2009), are found locally in water depths less than about 15 

m. These units are concentrated at the mouths of the Santa Clara and Ventura Rivers and a few smaller coastal watersheds to the 

northwest, and they are inferred to represent wave-winnowed lags of deltaic sediment. It is likely that these deposits are ephemeral and are commonly covered by finer grained sediment. However, a few areas of unit Qmsc between Ventura and Pitas Point 

are not obviously tied to coastal watersheds. One large area in particular is characterized by high rugosity (see Box A on sheet 5) 

and high backscatter (see sheet 3); camera ground-truth surveying (see fig. 2 on sheet 6) reveals that this area consists of 

boulders, cobbles, gravel, and sand. The area lies immediately offshore of steep slopes underlain by variably consolidated 

Pliocene and Pleistocene deposits (sand, gravel, cobbles) of the Pico, Santa Barbara, and Saugus Formations (onshore units Tp, 

QTsb, and Qs, respectively), which are highly susceptible to landsliding (Tan and others, 2003a,b); thus, this area most likely 

represents wave-winnowed landslide deposits. It is also possible that these high-backscatter areas are partly underlain by 

bedrock, as is inferred on sheet 7. The steep onshore slopes are immediately north of, and in the hanging wall of, the active Pitas 

Point Fault, a location that undoubtedly has contributed to slope instability. 

The seafloor bedrock exposures south and west of Punta Gorda are inferred to consist of the Pico Formation (unit Tp; Tan 

and others, 2003a,b), on the basis of their backscatter, rugosity, and relief, as well as adjacent exposures of unit Tp in coastal 

bluffs and platforms and their similar location along the axis of the Rincon–Ventura Avenue Anticline (Tan and others, 2003a). A 

few shallow (less than 10 m deep) areas offshore between Punta Gorda and Pitas Point are inferred to be underlain by a composite unit (Qms/Tp) consisting of the Pico Formation overlain by a thin (probably ephemeral) marine-sediment layer.

The Offshore of Ventura map area is in the Ventura Basin, in the southern part of the Western Transverse Ranges geologic 

province, which is north of the California Continental Borderland (Fisher and others, 2009). This province has undergone 

significant north-south compression since the Miocene, and recent GPS data suggest north-south shortening of about 6 to 10 

mm/yr (Larson and Webb, 1992; Donnellan and others, 1993). The active, north-verging Oak Ridge Fault and the south-verging 

Pitas Point Fault (continuous with the onshore Ventura Fault) are two of the structures on which this shortening occurs (see, for 

example, Sorlien and others, 2000; Fisher and others, 2005, 2009). High-resolution seismic-reflection profiles (sheet 8) reveal 

that neither fault ruptures the surface; instead, the surface expression of each fault is a narrow, asymmetric fold that involves the 

uppermost Pleistocene and Holocene (younger than 21 ka) sedimentary section. Both structures are inferred to be parts of long 

fault systems that extend for more than 100 km, representing important potential earthquake hazards (see, for example, Fisher 

and others, 2009). Shortening is also occurring on the Montalvo Fault and Anticline system along the southeast edge of the map 

area (part of the broader Oak Ridge Fault Zone; Yeats, 1998) and on the Rincon–Ventura Avenue Anticline (see, for example, 

Rockwell and others, 1988), which crosses the northwest edge of the map area. 

REFERENCES CITED

Barnard, P.L., Revell, D.L., Hoover, D., Warrick, J., Brocatus, J., Draut, A.E., Dartnell, P., Elias, E., Mustain, N., Hart, P.E., and 

Ryan, H.F., 2009, Coastal processes study of Santa Barbara and Ventura counties, California: U.S. Geological Survey 

Open-File Report 2009–1029, 926 p., available at http://pubs.usgs.gov/of/2009/1029/.

Cacchione, D.A., Drake, D.E., Grant, W.D., and Tate, G.B., 1984, Rippled scour depressions of the inner continental shelf off 

Central California: Journal of Sedimentary Petrology, v. 54, p. 1,280–1,291.

Dahlen, M.Z., 1992, Sequence stratigraphy, depositional history, and middle to late Quaternary sea levels of the Ventura shelf, 

California: Quaternary Research, v. 38, p. 234–245.

Dibblee, T.W., Jr., 1986, Geologic map of the Carpinteria quadrangle, Santa Barbara County, California: Santa Barbara, Dibblee 

Geological Foundation Map DF–04, scale 1:24,000.

Donnellan, A., Hager, B.H., and King, R.W., 1993, Discrepancy between geologic and geodetic deformation rates in the Ventura 

basin: Nature, v. 346, p. 333–336.

Fisher, M.A., Greene, H.G., Normark, W.R., and Sliter, R.W., 2005, Neotectonics of the offshore Oak Ridge fault near Ventura, 

southern California: Bulletin of the Seismological Society of America, v. 95, p. 739–744.

Fisher, M.A., Sorlien, C.C., and Sliter, R.W., 2009, Potential earthquake faults offshore southern California from the eastern 

Santa Barbara channel to Dana Point, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban ocean—The 

Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 271–290.

Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and 

Jenkins, C., 2005, Detailed investigations of sorted bedforms or “rippled scour depressions,” within the Marthas’s Vineyard 

Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461–484.

Larson, K.M., and Webb, F.H., 1992, Deformation in the Santa Barbara Channel from GPS measurements 1987-1991: 

Geophysical News Letters, v. 19, p. 1,491–1,494.

Minor, S.A., Kellogg, K.S., Stanley, R.G., Gurrola, L.D., Keller, E.A., and Brandt, T.R., 2009, Geologic map of the Santa 

Barbara coastal plain area, Santa Barbara County, California: U.S. Geological Survey Scientific Investigations Map 3001, 

scale 1:25,000, 1 sheet, pamphlet 38 p., available at http://pubs.usgs.gov/sim/3001/ .

Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmerman, M., Williams, S.J., and Field, M.E., 2006, usSEABED: Pacific Coast 

(California Oregon, Washington) offshore surficial-sediment data release: U.S. Geological Survey Data Series 182, 

available at http://pubs.usgs.gov/ds/2006/182/.

Rockwell, T.K., Keller, E.A., and Dembroff, G.R., 1988, Quaternary rate of folding of the Ventura Avenue anticline, western 

Transverse Ranges, southern California: Geological Society of America Bulletin, v. 100, p. 850–858.

Slater, R.A., Gorsline, D.S., Kolpack, R.L., and Shiller, G.I., 2002, Post-glacial sediments of the California shelf from Cape San 

Martin to the US-Mexico border: Quaternary International, v. 92, p. 45–61.

Sommerfield, C.R., Lee, H.J., and Normark, W.R., 2009, Postglacial sedimentary record of the southern California continental 

shelf and slope, Point Conception to Dana Point, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban 

ocean—The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 89–116.

Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S., and Hopps, T.E., 2000, Map restoration of folded and faulted late 

Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California: Geological Society of America 

Bulletin, v. 112, p. 1,080–1,090.

Tan, S.S., and Clahan, K.B., 2004, Geologic map of the White Ledge Peak 7.5' quadrangle, Santa Barbara and Ventura Counties, 

California—A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at 

http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm.

Tan, S.S., Jones, T.A., and Clahan, K.B., 2003a, Geologic map of the Ventura 7.5' quadrangle, Ventura County, California—A 

digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at 

http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm.

Tan, S.S., Jones, T.A., and Clahan, K.B., 2003b, Geologic map of the Pitas Point 7.5' quadrangle, Ventura County, California—A 

digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at 

http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.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.

Warrick, J.A., and Farnsworth, K.L., 2009a, Sources of sediment to the coastal waters of the Southern California Bight, in Lee, 

H.J., and Normark, W.R., eds., Earth science in the urban ocean—The Southern California Continental Borderland: 

Geological Society of America Special Paper 454, p. 39–52.

Weber, K.M., List, J.H., and Morgan, K.L., 2005, An operational Mean High Water datum for determination of shoreline 

position from topographic lidar data: U.S. Geological Survey Open-File Report 2005–1027, accessed April 5, 2011, at 

http://pubs.usgs.gov/of/2005/1027/.

Yeats, R.S., 1998, North-vergent thick-skinned or south-vergent thin-skinned Oak Ridge fault—A view from the coast, in 

Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, 

California: American Association of Petroleum Geologists, Pacific Section and Coast Geological Society, Miscellaneous 

Publication 46, p. 143–152.

LIST OF MAP UNITS

[See Description of Map Units (chapter 8, in pamphlet) for complete map-unit descriptions]

OFFSHORE GEOLOGIC AND GEOMORPHIC 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/Tp indicates that thin sheet of Qms overlies 

Tp)] 

Artificial fill (late Holocene)—Rock, sand, and mud; placed and (or) dredged

Platform debris (late Holocene)—Mixed coarse sediment and construction debris surrounding Rincon Island 

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

Coarse-grained marine nearshore and shelf deposits (late Holocene)—Coarse sand, gravel, and cobbles

Fine-grained marine shelf deposits (late Holocene)—Mostly mud to muddy sand

Marine shelf scour depressions (late Holocene)—Inferred to be coarse sand and gravel in low-relief scours

Pico Formation (Pliocene)

ONSHORE GEOLOGIC AND GEOMORPHIC UNITS 

[Units are compiled from Dibblee (1986), Tan and others (2003a,b), and Tan and Clahan (2004). Unit ages, which are from 

Tan and others (2003a,b) and Minor and others (2009), reflect local stratigraphic relations]

Artificial fill (late Holocene)—Engineered and (or) nonengineered

Beach deposits (late Holocene)—Unconsolidated, loose, fine- to coarse-grained sand; well sorted

Wash deposits (late Holocene)—Unconsolidated silt, sand, and gravel. Located in major active river channels

Coastal eolian sand dune-deposits (late Holocene)—Well-sorted, loose sand and silt

Coastal-estuarine deposits (late Holocene)—Silty clay

Alluvial fan deposits (late Holocene)—Moderately to poorly bedded sandy clay with some gravel

Wash deposits (Holocene)—Unconsolidated silt, sand, and gravel

Alluvium and colluvium, undivided (Holocene)—Primarily sandy clay with some gravel

Stream-terrace deposits (Holocene)—Clayey sand and sandy clay with gravel

Alluvial fan deposits (Holocene)—Moderately to poorly sorted sandy clay with gravel

Paralic deposits of Sea Cliff marine terrace (Holocene)—Sandy clay with some gravel

Landslide deposits and colluvium, undivided (Holocene and Pleistocene)—Weathered rocks and soil

Paralic deposits of Punta Gorda marine terrace (late Pleistocene)—Clayey sand with gravel lenses

Older alluvial deposits (late and middle Pleistocene)—Silt, sand, clay, and gravel

Older alluvial deposits (middle and early Pleistocene)—Gravel, sand, silt, clay, and boulders

Colluvium (Pleistocene)—Silt, sand, clay, and gravel

Saugus Formation (Pleistocene)—Sandstone and siliceous shale, gravel, and cobbles

Las Posas Formation (Pleistocene)—Sandstone and gravelly sand

Santa Barbara Formation (Pleistocene and Pliocene)—Claystone; locally contains shale fragments

Pico Formation, undivided (Pliocene)—Claystone, siltstone, and sandstone; locally pebbly

Sandstone 

Sandstone and conglomerate

Sisquoc Formation (Pliocene and Miocene)—Silty shale and claystone

Monterey Formation, undivided (Miocene)—Siliceous and diatomaceous shale, sandstone, and limestone

Upper unit (late Miocene)—Mainly diatomaceous mudstone and shale

Lower, calcareous unit (middle and early Miocene)—Predominantly mudstone and shale

Rincon Shale (Miocene)—Shale and siltstone

Vaqueros Formation (Miocene)—Sandstone; locally calcareous

Sespe Formation (Oligocene to late Eocene)—Sandstone, siltstone, and claystone; locally pebbly

EXPLANATION OF MAP SYMBOLS

Contact—Solid where location is certain, long-dashed where location is approximate, short-dashed where 

location is inferred, dotted where location is concealed

Fluvial-terrace scarp—Denotes fluvial terrace within unit Qt; in places, also forms terraced alluvial contact 

between units Qt and Qa. Dashed where location is approximate, queried where uncertain. Hachures point 

downscarp

Landslide complex—Arrow(s) show direction of downslope movement; pattern shows area of slip surface and 

direction of slip

Fault—Long-dashed where location is approximate, short-dashed where location is inferred, dotted where 

location is concealed, queried where uncertain

Folds—Solid where location is certain, long-dashed where location is approximate, short-dashed where 

location is inferred, dotted where location is concealed

Antiform

Synform 

Monoform

Former shoreline or marine limit

Approximate modern shoreline—Defined as Mean High Water (MHW) (+1.33 m), North American Vertical 

Datum of 1988 (NAVD 1988)

3-nautical-mile limit of California’s State Waters 

Area of “no data”—Areas beyond the 3-nautical-mile limit of California’s State Waters were not mapped as 

part of the California Seafloor Mapping Program

OFFSHORE GEOLOGIC AND GEOMORPHIC UNITS ONSHORE GEOLOGIC AND GEOMORPHIC UNITS

CORRELATION OF MAP UNITS

Qw1 Qa Qt

af Qb Qw2 Qe Qes

Tsp

Tv

Tr

Tml

Tmu

Tsq

QTsb

Qlp

Qs

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Qoa2

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Qymp

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Tpsc

Qyf

Qf

Tp

Tm

Tp

af pd Qms Qmsc Qmsf Qmss

Pliocene

Pleistocene

Miocene

Oligocene

Holocene

[See Description of Map Units (chapter 8, in pamphlet) for precise unit ages]

Eocene

QUATERNARY

TERTIARY

120° 119°40' 119°20' 119°

34°

34°20'

Kilometers 0 5 10

0 4 8 Nautical Miles

Santa Barbara Channel

Santa Barbara

Ventura

CALIF.

MAP LOCATION

Limit of California’s

 State Waters

Santa Cruz Island Santa Rosa Island

Area of

 Map

Anacapa

 Island

1

U.S. Geological Survey;

2

California Geological Survey 

Offshore and Onshore Geology and Geomorphology, Offshore of Ventura Map Area, California

 By

Samuel Y. Johnson,1 Andrew C. Ritchie,1 Gordon G. Seitz,2 and Carlos I. Gutierrez2

2013

ONE MILE = 0.869 NAUTICAL MILES

BATHYMETRIC CONTOUR INTERVAL 10 METERS

1 .5 0 1 KILOMETER

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 1/2 0 1 MILE

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2013

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

Offshore geology and geomorphology mapped by Samuel Y. 

Johnson and Andrew C. Ritchie, 2010-2011. Onshore 

geology and geomorphology compiled by Gordon G. Seitz 

and Carlos I. Guiterrez from Dibblee (1986), Tan and others 

(2003a,b), and Tan and Clahan (2004). Bathymetric contours 

by Andrew C. Ritchie, 2011 

GIS database and digital cartography by Andrew C. Ritchie 

and Eleyne L. Phillips

Edited by Taryn A. Lindquist

Manuscript approved for publication March 11, 2013 

Onshore elevation data from NOAA Coastal Services 

Center (data collected by EarthData International in 

2002-2003). Offshore shaded-relief bathymetry from map 

on sheet 2, this report. California's State Waters limit 

from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 11N

NOT INTENDED FOR NAVIGATIONAL USE

20

10

30

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[Oak Ridge Fault trend]

[Pitas Point Fault trend]

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Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss

Qmss Qmss

Qmss

Qmss

Qmss

Qmss

Qmsc

Qmsc

Qmsc

Qmsc

Qmsc

Qmsc

Qmsc

Qms/Tp

Tp

Tp Tp

Qmsc

Qmsc

pd

Tp

Tp

Qms/Tp

Qmsf

Qms

Qms

af

Tp

af

Qmsc

Qms/Tp?

Qms/Tp

Qms/Tp?

Qms/Tp?

Qms/Tp?

Qms

Qa Qa

Qlp

Qa

Qa

Qa

QTsb

Montalvo Fault

Pitas

Point

Punta

Gorda

Rincon–Ventura Avenue Anticline

Montalvo Anticline

Qomp

QTsb

119°25' 119°20' 119°15'

119°25' 119°20'

34°15'

34°20'

34°15'

34°20'

Ventura

Harbor

Ventura

Santa Clara River

V

e

n t u

r

a

R

i

v

e

r

Lake Casitas

Scientific Investigations Map 3254 

Sheet 10 of 11

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey