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 https://doi.org/10.3133/ofr20181023

Suggested Citation: Johnson, S.Y., and Hartwell, S.R., 2018, Local (Offshore of Gaviota map area) and regional (offshore from Point 

Conception to Hueneme Canyon) shallow-subsurface geology and structure, Santa Barbara Channel, California, sheet 8 in Johnson, 

S.Y., Dartnell, P., Cochrane, G.R., Hartwell, S.R., Golden, N.E., Kvitek, R.G., and Davenport, C.W. (S.Y. Johnson and S.A. Cochran, eds.), 

California State Waters Map Series—Offshore of Gaviota, California: U.S. Geological Survey Open-File Report 2018–1023, pamphlet 

41 p., 9 sheets, scale 1:24,000, https://doi.org/10.3133/ofr20181023.

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20181023

DISCUSSION

This sheet includes maps that show the thickness and the depth to base of uppermost 

Pleistocene and Holocene (in other words, post–Late Glacial Maximum) deposits for the 

Offshore of Gaviota map area (Maps A, B), as well as for a larger area that extends about 130 

km along the coast from Hueneme Canyon to Point Conception (Maps D, E) to establish a 

regional context. To make these maps, water bottom and depth to base of the uppermost 

Pleistocene and Holocene sediment layer were mapped from seismic-reflection profiles (sheet 

7). The difference in the two horizons was exported for every shot point as XY coordinates 

(UTM zone 10) and two-way travel time (TWT). The thickness of the uppermost Pleistocene 

and Holocene unit (Maps B, E) was determined by applying a sound velocity of 1,600 m/sec to 

the TWT. The thickness points were interpolated to a preliminary continuous surface, overlaid 

with zero-thickness bedrock outcrops (see sheet 9), and contoured, following the methodology 

of Wong and others (2012). Data within Hueneme Canyon were excluded from the contouring 

because the seismic-reflection data are too sparse to adequately image the highly variable 

changes in sediment thickness that characterize the canyon (Maps D, E).

Several factors required manual editing of the preliminary sediment-thickness maps to 

make the final products. The Red Mountain Fault Zone (RMFZ), Pitas Point Fault (PPF), and 

Oak Ridge Fault (ORF) disrupt the sediment sequence in the region (Maps D, E). The data 

points also are dense along tracklines (about 1 m apart) and sparse between tracklines (1–2 km 

apart), resulting in contouring artifacts. To incorporate the effect of the faults, to remove 

irregularities from interpolation, and to reflect other geologic information and complexity, the 

resulting interpolated contours were modified. Contour modifications and regridding were 

repeated several times to produce the final regional sediment-thickness map (Wong and others, 

2012). Data for the depth to base of the uppermost Pleistocene and Holocene unit (Maps A, D) 

were generated by adding the thickness data to water depths determined by multibeam bathymetry (see sheet 1).

In the Offshore of Gaviota map area, the thickness of the uppermost Pleistocene and 

Holocene sediments on the continental shelf ranges from 0 to 36 m (Map B). Mean sediment 

thickness on the shelf in the map area is 9.9 m, and the total sediment volume on the shelf is 

853×106

 m3. The thickest sediment in the map area (about 36 m) is found within the Gaviota 

sediment bar. The primary sediment source, Cañada de la Gaviota, is the largest coastal 

watershed (about 52 km2; Warrick and Mertes, 2009) between the Ventura River and Point 

Conception. Sediment thins markedly and is locally absent on the shelf both southeast and 

northwest of the Gaviota sediment bar, commonly forming only a thin veneer over bedrock 

outcrops. 

Five different “domains” of sediment thickness, which are bounded either by faults or by 

Hueneme Canyon, are recognized on the regional maps (Maps D, E): (1) north of the south 

strand of the Red Mountain Fault Zone; (2) between the south strand of the Red Mountain Fault 

Zone and the Pitas Point Fault; (3) between the Pitas Point and Oak Ridge Faults; (4) between 

the Oak Ridge Fault and Hueneme Canyon; and (5) south of Hueneme Canyon. Table 6–1 (in 

pamphlet) shows the area of these five domains, along with estimates of their mean sediment 

thicknesses and total sediment volumes. These data highlight the contrast among three general 

zones of sediment thickness: (1) the uplifted, sediment-poor Santa Barbara and Point Conception shelf (domain 1; mean sediment thickness of 4.2 m); (2) a transitional zone (domain 2; 

mean sediment thickness of 18.0 m); and (3) the subsiding, sediment-rich delta and shelf 

offshore of the Ventura and Santa Clara Rivers and Calleguas Creek (domains 3, 4, and 5; mean 

sediment thicknesses of 39.2, 38.9, and 28.3 m, respectively). 

The regional pattern of faults and of earthquakes occurring between 1932 and 2016 that 

have inferred or measured magnitudes greater than 2.0 is shown on Map C. Fault locations are 

based on our mapping within California’s State Waters and on a generalized compilation that 

includes the mapping of Heck (1998), Minor and others (2009), and Jennings and Bryant 

(2010). Earthquake data are from the U.S. Geological Survey (2016). Although earthquake 

locations have been determined by the CalTech network since 1932, significantly greater 

precision began in 1969 with installation of a U.S. Geological Survey (USGS) seismographic 

network (see, for example, Lee and Vedder, 1973; Sylvester, 2001; U.S. Geological Survey, 

2016). Epicentral data indicate that seismicity in the Santa Barbara Channel region is characterized by earthquake swarms, relatively frequent minor earthquakes, and infrequent major 

earthquakes.

Three significant earthquakes affected the Santa Barbara Channel area prior to 1932 (the 

year of the earliest earthquake in the U.S. Geological Survey [2016] catalog): in 1812, 1857 

(the Fort Tejon earthquake on the San Andreas Fault), and 1925 (Stover and Coffman, 1993). 

Sylvester and others (1970) reported a location in the northern Santa Barbara Channel for the 

1925 event (M6.3), as well as for a 1941 earthquake (~M5.5, 7/1/1941) about 7 km offshore 

and 15 km southeast of Santa Barbara, the largest earthquake shown on Map C (sheet 8). In 

addition, Sylvester and others (1970) documented a swarm of 62 earthquakes (M2.5–M5.2) 

that occurred between 6/26/1968 and 8/3/1968, which also were located 10 to 15 km south 

(offshore) of Santa Barbara. The largest recorded event in the Offshore of Gaviota map area 

(M3.1) occurred on 11/4/1987, about 7 km south of Gaviota (U.S. Geological Survey, 2016). 

REFERENCES CITED

Heck, R.G., 1998, Santa Barbara Channel regional formline map, top Monterey Formation, 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, 1 plate.

Jennings, C.W., and Bryant, W.A., 2010, Fault activity map of California: California 

Geological Survey Geologic Data Map No. 6, scale 1:750,000, available at 

http://www.conservation.ca.gov/cgs/cgs_history/Pages/2010_faultmap.aspx.

Lee, W.H.K., and Vedder, J.G., 1973, Recent earthquake activity in the Santa Barbara Channel 

region: Bulletin of the Seismological Society of America, v. 63, p. 1,757–1,773.

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/.

Stover, C.W. and Coffman, J.L., 1993, Seismicity of the United States, 1568-1989 (revised): 

U.S. Government Printing Office, 418 p.

Sylvester, A.G., 2001, Catalog of Santa Barbara earthquakes—1800 to 1960: Santa Barbara, 

University of California, Santa Barbara database, accessed March 2016 at 

http://projects.crustal.ucsb.edu/sb_eqs/SBEQCatlog/SBEQCATINTRO.html.

Sylvester, A.G., Smith, S.S., and Scholz, C.H., 1970, Earthquake swarm in the Santa Barbara 

Channel, California, 1968: Bulletin of the Seismological Society of America, v. 60, p. 

1,047–1,060.

U.S. Geological Survey, 2016, Earthquake catalog: U.S. Geological Survey database, accessed 

June 14, 2016, at https://earthquake.usgs.gov/earthquakes/search/.

Warrick, J.A., and Mertes, L.A.K., 2009, Sediment yield from the tectonically active semiarid 

Western Transverse Ranges of California: Geological Society of America Bulletin, v. 121, 

p. 1,054–1,070.

Wong, F.L., Phillips, E.L., Johnson, S.Y, and Sliter, R.W., 2012, Modeling of depth to base of 

Last Glacial Maximum and seafloor sediment thickness for the California State Waters 

Map Series, eastern Santa Barbara Channel, California: U.S. Geological Survey Open-File 

Report 2012–1161, 16 p., available at http://pubs.usgs.gov/of/2012/1161/.

120°30' 120° 119°30'

34°

34°30'

Limit of California’s

State Waters

Kilometers 0 5 10

Santa Barbara Channel

Area of

Map

Santa Barbara CALIF.

MAP LOCATION

Anacapa Is.

Santa Cruz Is.

Santa Rosa Is.

San Miguel Is.

Local (Offshore of Gaviota Map Area) and Regional (Offshore from Point Conception to Hueneme Canyon)

Shallow-Subsurface Geology and Structure, Santa Barbara Channel, California

By

Samuel Y. Johnson and Stephen R. Hartwell

2018

ONE MILE = 0.869 NAUTICAL MILES

1 0.5 0 1 KILOMETER

7000 3500 0 7000 FEET

2 1 0 2 MILES

SCALE 1:50 000

ONE MILE = 0.869 NAUTICAL MILES

20 10 0 20 KILOMETERS

80000 60000 40000 20000 0 80000 FEET

20 10 0 20 MILES

SCALE 1:300 000

ONE MILE = 0.869 NAUTICAL MILES

10 5 0 10 KILOMETERS

40000 30000 20000 10000 0 40000 FEET

10 5 0 10 MILES

SCALE 1:200 000

APPROXIMATE MEAN

DECLINATION, 2018 

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

APPROXIMATE MEAN

7DECLINATION, 2018 MAGNETIC NORTH

TRUE NORTH

APPROXIMATE MEAN

DECLINATION, 2015

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

8

12 / ° 1 2

Compiled by Stephen R. Hartwell and Samuel 

Y. Johnson, 2016

Onshore elevation data from National Oceanic and 

Atmospheric Administration (NOAA) Office for Coastal 

Management’s Digital Coast (available at 

http://www.csc.noaa.gov/digitalcoast/data/coastallidar) 

and from U.S. Geological Survey’s National Elevation 

Dataset (available at http://ned.usgs.gov/). California's 

State Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 11N

Onshore elevation data from National Oceanic and 

Atmospheric Administration (NOAA) Office for Coastal 

Management’s Digital Coast (available at 

http://www.csc.noaa.gov/digitalcoast/data/coastallidar) 

and from U.S. Geological Survey’s National Elevation 

Dataset (available at http://ned.usgs.gov/). 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 10N

NOT INTENDED FOR NAVIGATIONAL USE

Depth and thickness mapped by Samuel Y. 

Johnson and Stephen R. Hartwell, 2016

GIS database and digital cartography by Stephen 

R. Hartwell

Onshore elevation data from National Oceanic and Atmospheric Administration (NOAA) Office for Coastal 

Management’s Digital Coast (available at http://www.csc.noaa.gov/digitalcoast/data/coastallidar) and from U.S. 

Geological Survey’s National Elevation Dataset (available at http://ned.usgs.gov/). Offshore shaded-relief 

bathymetry from data collected by Monterey Bay Aquarium Research Institute in 2002, by U.S. Geological Survey in 

2006, and by California State University, Monterey Bay, Seafloor Mapping Lab in 2006–2007. California's State 

Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 11N

NOT INTENDED FOR NAVIGATIONAL USE

Depth and thickness mapped by Samuel Y. Johnson, Eleyne L. Phillips, and Stephen 

R. Hartwell, 2010–2016

GIS database and digital cartography by Andrew C. Ritchie, Eleyne L. Phillips, 

Florence L. Wong, and Stephen R. Hartwell

Manuscript approved for publication February 12, 2018

119°

119°

119°10'

119°10'

119°20'

119°20'

119°30'

119°30'

119°40'

119°40'

119°50'

119°50'

120°

120°

120°10'

120°10'

120°20'

120°20'

120°30'

120°30'

34°30'

34°40'

34°10'

34°

34°40'

34°30'

34°20'

34°20'

34°

0 – 0.1

0.1 – 2.5

2.5 – 5

5 – 7.5

7.5 – 10

10 – 12.5

12.5 – 15

15 – 17.5

17.5 – 20

20 – 22.5

22.5 – 25

25 – 27.5

27.5 – 30

30 – 32.5

32.5 – 35

35 – 37.5

37.5 – 40

40 – 42.5

42.5 – 45

45 – 47.5

47.5 – 50

50 – 52.5

52.5 – 55

55 – 57.5

EXPLANATION

Thickness of uppermost Pleistocene

and Holocene sediment, in meters

Thickness contours

Index (10-m intervals)

Intermediate

Fault—ORF, Oak Ridge Fault; PPF, 

Pitas Point Fault; RMFZ, Red 

Mountain Fault Zone

Approximate shoreline

3-nautical-mile limit of California’s 

State Waters

Offshore of 

Gaviota map 

area and area

of Maps A, B

RMFZ

PPF

ORF

Ventura

Oxnard

Santa 

Barbara

Goleta

 Point

Conception

Hueneme 

Canyon

Map E

34°10'

119°

119°

119°10'

119°10'

119°20'

119°20'

119°30'

119°30'

119°40'

119°40'

119°50'

119°50'

120°

120°

120°10'

120°10'

120°20'

120°20'

120°30'

120°30'

34°30'

34°40'

34°10'

34°

34°40'

34°30'

34°20'

34°20'

34°10'

34°

-190 – -185

-185 – -180

-180 – -175

-175 – -170

-170 – -165

-165 – -160

-160 – -155

-155 – -150

-150 – -145

-145 – -140

-140 – -135

-135 – -130

-130 – -125

-125 – -120

-120 – -115

-115 – -110

-110 – -105

-105 – -100

-100 – -95

-95 – -90

-90 – -85

-85 – -80

-80 – -75

-75 – -70

-70 – -65

-65 – -60

-60 – -55

-55 – -50

-50 – -45

-45 – -40

-40 – -35

-35 – -30

-30 – -25

-25 – -20

-20 – -15

-15 – -10

-10 – -5

EXPLANATION

Depth to base of uppermost Pleistocene

and Holocene sediment, in meters

Depth-to-base contours

Index (20-m intervals)

Intermediate

Fault—ORF, Oak Ridge Fault; PPF, 

Pitas Point Fault; RMFZ, Red 

Mountain Fault Zone

Approximate shoreline

3-nautical-mile limit of California’s 

State Waters

Offshore of

Gaviota map 

area and area

of Maps A, B

RMFZ

PPF

ORF

Ventura

Oxnard

Santa 

Barbara

Goleta

 Point

Conception

Hueneme 

Canyon

Map D

120°20' 119°10'

119°10'

119°20'

119°20'

119°30'

119°30'

119°40'

119°40'

119°50'

119°50'

120°

120°10' 120°

120°20'

120°20'

120°30'

120°30'

120°40'

120°40'

34°30'

34°30'

34°20'

34°20'

34°10'

34°10'

34°

34°

33°50'

3-nautical-mile 

limit of California’s 

State Waters

Fault

EXPLANATION

Regional faults and 

earthquake epicenters, 

1932 – 2016

MAGNITUDE

2.0 - 2.5

2.5 - 3.0

3.0 - 3.5

3.5 - 4.0

4.0 - 5.5

Map C

Offshore of 

Gaviota map

area and area

of Maps A, B

120°10'

Approximate area 

of Maps D, E

33°50'

120°15'

120°15'

120°20'

120°20'

34°30'

34°30'

34°25'

34°25'

Map B

Molino Anticline

Government Point Syncline

south strand of Santa Ynez Fault

0 – 0.1

0.1 – 2.5

2.5 – 5

5 – 7.5

7.5 – 10

10 – 12.5

17.5 – 20

20 – 22.5

22.5 – 25

25 – 27.5

EXPLANATION

Thickness of uppermost Pleistocene 

and Holocene sediment, in meters

Thickness contours

Index (10-m intervals)

Intermediate

Fault—Dashed where location is inferred; 

dotted where location is concealed

Anticline—Dotted where location is 

concealed

Syncline—Dotted where location is 

concealed

Approximate shoreline

3-nautical-mile limit of California’s 

State Waters

Area of “no data”—Areas where data are 

insufficient for contouring

12.5 – 15

15 – 17.5

27.5 – 30

30 – 32.5

32.5 – 35

35 – 37.5

 Gaviota

State Park

120°15'

120°15'

120°20'

120°20'

34°30'

34°30'

34°25'

34°25'

Map A

Molino Anticline

Government Point Syncline

south strand of Santa Ynez Fault

EXPLANATION

Depth to base of uppermost Pleistocene and 

Holocene sediment, in meters

Depth-to-base contours

Index (20-m intervals)

Intermediate

Fault—Dashed where location is inferred; 

dotted where location is concealed

Anticline—Dotted where location is concealed

Syncline—Dotted where location is concealed

Approximate shoreline

3-nautical-mile limit of California’s 

State Waters

Area of “no data”—Areas where data are 

insufficient for contouring

-65 – -60

-60 – -55

-55 – -50

-50 – -45

-45 – -40

-40 – -35

-35 – -30

-30 – -25

-25 – -20

-20 – -15

-15 – -10

-100 – -95

-95 – -90

-90 – -85

-85 – -80

-80 – -75

-75 – -70

-70 – -65

-110 – -105

-105 – -100

-115 – -110

-120 – -105

-125 – -125

 Gaviota

State Park

Open-File Report 2018–1023

Sheet 8 of 9

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey