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://dx.doi.org/10.3133/ofr20151232

Suggested Citation: Erdey, M.D., and Cochrane, G.R., 2015, Seafloor character, Offshore of Pigeon Point map area, California, sheet 5 

in Cochrane, G.R., Watt, J.T., Dartnell, P., Greene, H.G., Erdey, M.D., Dieter, B.E., Golden, N.E., Johnson, S.Y., Endris, C.A., Hartwell, 

S.R., Kvitek, R.G., Davenport, C.W., Krigsman, L.M., Ritchie, A.C., Sliter, R.W., Finlayson, D.P., and Maier, K.L. (G.R. Cochrane and S.A. 

Cochran, eds.), California State Waters Map Series—Offshore of Pigeon Point, California: U.S. Geological Survey Open-File Report 

2015–1232, pamphlet 40 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20151232.

ISSN 2331-1258 (online) 

http://dx.doi.org/10.3133/ofr20151232

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.

Rock and boulders, 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 1

Rock and boulders, rugose; 

Depth Zone 3, Slope Class 2

Mixed smooth sediment 

and rock; Depth Zone 3, 

Slope Class 1

Medium- to coarse-grained 

rippled 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. Parallel light and dark lines are data-processing artifacts. 

Interpreted substrate classes from figure 4 included for comparison.

Rock and boulders, 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 1

Rock and boulders, rugose; 

Depth Zone 3, Slope Class 2

Mixed smooth sediment 

and rock; Depth Zone 3, 

Slope Class 1

Medium- to coarse-grained 

rippled sediment; 

Depth Zone 3, Slope Class 1 

Figure 4. Detailed view of substrate classes mapped offshore of Año Nuevo State Park (see Box B, on map, for 

location): Depth Zone 3 (30 to 100 m), Slope Class 1 (0°–5°), and Slope Class 2 (5°–30°). Fine- to medium-grained 

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

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

Rock and boulders, 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 1

Rock and boulders, rugose; 

Depth Zone 3, Slope Class 2

Mixed smooth sediment 

and rock; Depth Zone 3, 

Slope Class 1

Medium- to coarse-grained 

rippled 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). Interpreted 

substrate classes from figure 1 included for comparison.

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 1 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 1

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 1

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 2 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 2

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 2

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. Parallel gray lines are data-processing artifacts. Interpreted 

substrate classes from figure 1 included for comparison.

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 1 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 1

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 1

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 2 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 2

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 2

Figure 1. Detailed view of substrate classes mapped offshore of Año Nuevo State Park (see Box A, on map, for 

location): Depth Zone 2 (intertidal to 30 m), Slope Class 1 (0°–5°), and Slope Class 2 (5°–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 rock is shown in shades of pink. 

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 1 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 1

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 1

Rock and boulder, rugose; 

Depth Zone 2, Slope Class 2 

Mixed smooth sediment 

and rock; Depth Zone 2, 

Slope Class 2

Fine- to medium-grained 

smooth sediment; 

Depth Zone 2, Slope Class 2

BOX A

US Army Corps

of Engineers

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 and 3.

Fine- to mediumgrained smooth

sediment

Medium- to coarsegrained sediment

79.1 104.8 15.4 20.4 63.7 84.4

18.1 10.2 Rock and boulder, 

rugose

13.7 13.5 3.5

7.5

4.6

5.7 Mixed smooth

sediment and rock 3.5 4.6 2.2 2.9

 2.01.5 0.3 0.4 1.2 1.6

Total

percent sq km

Depth Zone 2

(water depth 0–30 m)

Depth Zone 3

(water depth 30–100 m)

percent of total sq km percent of total sq km

37°

36°40'

122°20' 122°

Santa Cruz

Monterey

Moss 

Landing

Pigeon

Point

Limit of California’s

State Waters

Area of

Map

CALIF.

MAP LOCATION

0 5 10 Kilometers

0 5 10Nautical Miles

121°40'

Monterey

Bay

20

(2.9 km2) is in Depth Zone 3. Rock and boulder, rugose (rock and boulder outcrops having high surficial 

complexity) makes up 13.7 percent (18.1 km2) of the map area: 10.2 percent (13.5 km2) is in Depth Zone 2, 

and 3.5 percent (4.6 km2) is in Depth Zone 3. Medium- to coarse-grained sediment (in scour depressions 

consisting of material that is coarser than the surrounding seafloor) makes up 1.5 percent (2.0 km2) of the map 

area: 0.3 percent (0.4 km2) is in Depth Zone 2, and 1.2 percent (1.6 km2) is in Depth Zone 3 (table 1).

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 medium- to 

coarse-grained sediment, with varying amounts of shell hash; in scour depressions 

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 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 medium- to 

coarse-grained sediment, with varying amounts of shell hash; in scour depressions

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 Pigeon Point map area in central California was produced using 

video-supervised, maximum-likelihood classification of the bathymetry and backscatter (intensity of return) signals 

from sonar systems (a summary of the video data collected for the purpose of supervising the classification is shown 

on sheet 6). 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), and Depth Zone 3 (30 to 100 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 Zones 4 and 5 (greater than 100 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 79.1 percent (104.8 km2) of the map area: 

15.4 percent (20.4 km2) is in Depth Zone 2, and 63.7 percent (84.4 km2) is in Depth Zone 3. 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 5.7 percent (7.5 km2) of the map area: 3.5 percent (4.6 km2) is in Depth Zone 2, and 2.2 percent 

Seafloor Character, Offshore of Pigeon Point Map Area, California

By

Mercedes D. Erdey and Guy R. Cochrane 

2015

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, 2015

MAGNETIC NORTH

13 / ° 1 2

TRUE NORTH

Seafloor character mapped by Mercedes D. Erdey, 2013. 

Bathymetric contours by Mercedes D. Erdey, 2014 

GIS database and digital cartography by Mercedes D. Erdey

Manuscript approved for publication December 4, 2015

Onshore elevation data from California Coastal Conservancy (available from 

National Oceanic and Atmospheric Administration [NOAA] Coastal Service 

Center’s Digital Coast 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

20

10

30

40

50

60

70

70

10

10

10

10

10

10

20

Año Nuevo 

 State Park

Pigeon Point

BOX B

BOX A

122°20'

122°20'

122°25'

122°25'

37°10'

37°10'

37°5'

37°5'

Open-File Report 2015–1232

Sheet 5 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey