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/ofr20181024

Suggested Citation: Hartwell, S.R., and Cochrane, G.R., 2018, Seafloor character, Offshore of Point Conception map area, California, 

sheet 5 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 Point Conception, California: U.S. Geological Survey Open-File 

Report 2018–1024, pamphlet 36 p., 9 sheets, scale 1:24,000, https://doi.org/10.3133/ofr20181024.

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20181024

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.

Figure 6. Rugosity (characterization of roughness derived from bathymetry) draped over shaded-relief bathymetry 

(see sheet 2) for same area as figure 4 (Box B on map). Rugosity values are displayed in muted “rainbow” color 

spectrum that ranges from purple (low rugosity) through green (medium rugosity) to red (high rugosity). Interpreted 

substrate classes from figure 4 included for comparison. Bathymetric contours (20, 30, and 40 m) shown for depth 

reference.

30

40

20

20

20

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Mixed smooth sediment and rock;

 Depth Zone 3, Slope Class 1 

Rock and boulder, rugose;

Depth Zone 2, Slope Class 1 

Anthropogenic, rugged;

Depth Zone 2, Slope Class 2

Medium- to coarse-grained

sediment; Depth Zone 3, Slope Class 1 

Figure 5. Acoustic-backscatter image (see sheet 3) draped over shaded-relief bathymetry (see sheet 2) for same 

area as figure 4 (Box B on map). Brighter areas indicate coarse-grained, rough, or hard seafloor; darker areas 

indicate unconsolidated (loosely packed) sediment. Interpreted substrate classes from figure 4 included for 

comparison. Bathymetric contours (20, 30, and 40 m) shown for depth reference.

30

40

20

20

20

20

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Mixed smooth sediment and rock;

 Depth Zone 3, Slope Class 1 

Rock and boulder, rugose;

Depth Zone 2, Slope Class 1 

Anthropogenic, rugged;

Depth Zone 2, Slope Class 2

Medium- to coarse-grained

sediment; Depth Zone 3, Slope Class 1 

Figure 4. Detailed view of substrate classes mapped east-southeast of Point Conception (see Box B, on map, for 

location): Depth Zones 2 and 3 (intertidal to 100 m), and Slope Classes 1 and 2 (0°–30°). Fine- to medium-grained 

smooth sediment is shown in shades of green; mixed smooth sediment and rock is shown in shades of tan; rugose 

rock and boulder is shown in shades of pink; medium- to coarse-grained sediment is shown in shades of yellow; 

and rugged anthropogenic features are shown in shades of purple. Bathymetric contours (20, 30, and 40 m) shown 

for depth reference.

30

40

20

20

20

20

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Mixed smooth sediment and rock;

 Depth Zone 3, Slope Class 1 

Rock and boulder, rugose;

Depth Zone 2, Slope Class 1 

Anthropogenic, rugged;

Depth Zone 2, Slope Class 2

Medium- to coarse-grained

sediment; Depth Zone 3, Slope Class 1 

BOX B

Figure 3. Rugosity (characterization of roughness derived from bathymetry) draped over shaded-relief bathymetry 

(see sheet 2) for same area as figure 1 (Box A on map). Rugosity values are displayed in muted “rainbow” color 

spectrum that ranges from purple (low rugosity) through green (medium rugosity) to red (high rugosity). 

Northwest-southeast-trending areas of high rugosity are data-collection artifacts. Interpreted substrate classes 

from figure 1 included for comparison. Bathymetric contours (40, 50, 60, and 70 m) shown for depth reference.

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Rock and boulder, rugose;

Depth Zone 3, Slope Class 1 

Mixed smooth sediment and rock;

Depth Zone 3, Slope Class 2

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 2

60

50

70

40

Figure 2. Acoustic-backscatter image (see sheet 3) draped over shaded-relief bathymetry (see sheet 2) for same 

area as figure 1 (Box A on map). Brighter areas indicate coarse-grained, rough, or hard seafloor; darker areas 

indicate unconsolidated (loosely packed) sediment. Northwest-southeast-trending areas of high backscatter are 

data-collection artifacts. Interpreted substrate classes from figure 1 included for comparison. Bathymetric 

contours (40, 50, 60, and 70 m) shown for depth reference.

60

50

70

40

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Rock and boulder, rugose;

Depth Zone 3, Slope Class 1 

Mixed smooth sediment and rock;

Depth Zone 3, Slope Class 2

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 2

60

50

70

40

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 1

Rock and boulder, rugose;

Depth Zone 3, Slope Class 1 

Mixed smooth sediment and rock;

Depth Zone 3, Slope Class 2

Fine- to medium-grained smooth

sediment; Depth Zone 3, Slope Class 2

Figure 1. Detailed view of substrate classes mapped west of Point Conception (see Box A, on map, for location): 

Depth Zone 3 (30 to 100 m), and Slope Classes 1 and 2 (0°–30°). Fine- to medium-grained smooth sediment is shown 

in shades of green; mixed smooth sediment and rock is shown in shades of tan; and rugose rock and boulder is 

shown in shades of pink. Bathymetric contours (40, 50, 60, and 70 m) shown for depth reference.

BOX A

Total Depth Zone 2

(water depth 0–30 m)

Depth Zone 3

(water depth 30–100 m)

Depth Zone 4

(water depth >100 m)

percent sq km percent of total sq km percent of total sq km percent of total sq km

83.0 107.1 13.2 17.0 64.5 83.3 5.3 6.8

7.9 10.1 3.1 4.1 4.7 6.1 0.1 0.1

8.8 11.4 4.7 6.1 2.2 2.9 1.9 2.4

0.2 0.3 0.2 0.2

0.1 0.1 <0.1 <0.1

Table 1. Coverage of classified seafloor, in square kilometers (sq km) and percent of total area, broken into California 

Marine Life Protection Act Depth Zones 2, 3, and 4.

<0.1 0.1 <0.1 <0.1

0.1 0.1

Fine- to mediumgrained smooth

sediment

Mixed smooth

sediment and

rock

Rock and

boulder, rugose

Medium- to

coarse-grained

sediment

Anthropogenic,

rugged

0.0 0.0

20

DESCRIPTION OF MAP UNITS

DEPTH ZONE 2—INTERTIDAL TO 30 METERS WATER DEPTH

SLOPE CLASS 1—0 TO 5 DEGREES

Fine- to medium-grained smooth sediment—Low backscatter, low rugosity; typically mud to 

medium-grained sand; often rippled and (or) burrowed

Mixed smooth sediment and rock—Moderate to very high backscatter, low rugosity; typically 

coarse-grained sand, gravel, cobbles, and bedrock

Rock and boulder, rugose—High backscatter, high rugosity; typically boulders and rugose 

bedrock

Medium- to coarse-grained sediment—Very high backscatter, low rugosity; typically mediumto coarse-grained sediment, with varying amounts of shell hash; in scour depressions

Rugged anthropogenic material—High backscatter, high rugosity; related to development by 

humans

DEPTH ZONE 3—30 METERS TO 100 METERS WATER DEPTH

SLOPE CLASS 1—0 TO 5 DEGREES

Fine- to medium-grained smooth sediment—Low backscatter, low rugosity; typically mud to 

medium-grained sand; often rippled and (or) burrowed

Mixed smooth sediment and rock—Moderate to very high backscatter, low rugosity; typically 

coarse-grained sand, gravel, cobbles, and bedrock

Rock and boulder, rugose—High backscatter, high rugosity; typically boulders and rugose 

bedrock

Medium- to coarse-grained sediment—Very high backscatter, low rugosity; typically mediumto coarse-grained sediment, with varying amounts of shell hash; in scour depressions

Rugged anthropogenic material—High backscatter, high rugosity; related to development by 

humans

SLOPE CLASS 2—5 TO 30 DEGREES

Fine- to medium-grained smooth sediment—Low backscatter, low rugosity; typically mud to 

medium-grained sand; often rippled and (or) burrowed

Mixed smooth sediment and rock—Moderate to very high backscatter, low rugosity; typically 

coarse-grained sand, gravel, cobbles, and bedrock

Rock and boulder, rugose—High backscatter, high rugosity; typically boulders and rugose 

bedrock

DEPTH ZONE 4—100 METERS TO 200 METERS WATER DEPTH

SLOPE CLASS 1—0 TO 5 DEGREES

Fine- to medium-grained smooth sediment—Low backscatter, low rugosity; typically mud to 

medium-grained sand; often rippled and (or) burrowed

Mixed smooth sediment and rock—Moderate to very high backscatter, low rugosity; typically 

coarse-grained sand, gravel, cobbles, and bedrock

Rugged anthropogenic material—High backscatter, high rugosity; related to development by 

humans

SLOPE CLASS 2—5 TO 30 DEGREES

Fine- to medium-grained smooth sediment—Low backscatter, low rugosity; typically mud to 

medium-grained sand; often rippled and (or) burrowed

Mixed smooth sediment and rock—Moderate to very high backscatter, low rugosity; typically 

coarse-grained sand, gravel, cobbles, and bedrock

Rock and boulder, rugose—High backscatter, high rugosity; typically boulders and rugose 

bedrock

EXPLANATION OF MAP SYMBOLS

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

seafloor mapping data; areas beyond 3-nautical-mile limit of California’s State Waters were 

not mapped as part of California Seafloor Mapping Program

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

Bathymetric contour (in meters)—Derived from modified 2-m-resolution bathymetry grid. 

Contour interval: 10 m

DISCUSSION

This seafloor-character map of the Offshore of Point Conception map area in southern California was 

produced using video-supervised, maximum-likelihood classification of the bathymetry and backscatter 

(intensity of return) signals from sonar systems (see Golden and Cochrane, 2013, for a summary of the video 

data collected for the purpose of supervising the classification). Rugosity (a GIS-derived characterization of 

roughness) and backscatter intensity were used as variants in the classification. The interpreted classifications 

were then draped over shaded-relief bathymetry (see sheet 2). 

The substrate classes mapped in this area have been divided into the following California Marine Life 

Protection Act depth zones: Depth Zone 2 (intertidal to 30 m), Depth Zone 3 (30 to 100 m), and Depth Zone 4 

(100 to 200 m). In addition, the following slope classes are represented on this map (Coastal and Marine 

Ecological Classification Standard slope zones are shown in parentheses): Slope Class 1, 0° to 5° (flat); and 

Slope Class 2, 5° to 30° (sloping). Depth Zone 1 (intertidal), Depth Zone 5 (greater than 200 m), and Slope 

Classes 3 to 5, greater than 30° (steeply sloping to overhang) are not present in this map area.

Fine- to medium-grained smooth sediment (sand and mud) makes up 83.0 percent (107.1 km2

) of the map 

area: 13.2 percent (17.0 km2) is in Depth Zone 2, 64.5 percent (83.3 km2) is in Depth Zone 3, and 5.3 percent 

(6.8 km2) is in Depth Zone 4. Mixed smooth sediment (sand and gravel) and rock (that is, sediment typically 

forming a veneer over bedrock, or rock outcrops having little to no relief) make up 7.9 percent (10.1 km2) of 

the map area: 3.1 percent (4.1 km2) is in Depth Zone 2, 4.7 percent (6.1 km2) is in Depth Zone 3, and 0.1 

percent (0.1 km2) is in Depth Zone 4. Rock and boulder, rugose (rocky outcrops, boulder fields, and asphalt 

mounds having high surficial complexity) makes up 8.8 percent (11.4 km2) of the map area: 4.7 percent (6.1 

km2) is in Depth Zone 2, 2.2 percent (2.9 km2) is in Depth Zone 3, and 1.9 percent (2.4 km2) is in Depth Zone 

4. Medium- to coarse-grained sediment makes up 0.2 percent (0.3 km2) of the map area: less than 0.1 percent 

(0.1 km2) is in Depth Zone 2, 0.2 percent (0.2 km2) is in Depth Zone 3, and less than 0.1 percent (<0.1 km2) is 

in Depth Zone 4. Rugged anthropogenic material makes up 0.1 percent (0.1 km2) of the map area: less than 0.1 

percent (<0.1 km2) is in Depth Zone 2, and 0.1 percent (0.1 km2) is in Depth Zone 3 (table 1).

REFERENCE CITED

Golden, N.E., and Cochrane, G.R., 2013, California Seafloor Mapping Program video and photograph portal: 

U.S. Geological Survey, Coastal and Marine Geology Program data portal, available at https://doi.org/

10.5066/F7J1015K.

Seafloor Character, Offshore of Point Conception Map Area, California

By

Stephen R. Hartwell and Guy R. Cochrane

2018

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, 2018

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

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

Seafloor character mapped in 2016 

GIS database and digital cartography by Nadine E. Golden 

and Stephen R. Hartwell

Manuscript approved for publication February 13, 2018 

20

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50

90

60

80

70

100

150

110

120

130

140

130

130

140

 Santa Ynez Mountains

 Point Conception

BOX B

BOX A

120°25'

120°25'

120°30'

120°30'

34°30'

34°30'

34°25'

34°25'

Open-File Report 2018–1024

Sheet 5 of 9

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey