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/3306/

Suggested Citation: Endris, C.A., Greene, H.G., Dieter, B.E., and Erdey, M.D., 2014, Potential marine benthic habitats, Offshore of San 

Gregorio map area, California, sheet 7 in Cochrane, G.R., Dartnell, P., Greene, H.G., Watt, J.T., Golden, N.E., Endris, C.A., Phillips, E.L., 

Hartwell, S.R., Johnson, S.Y., Kvitek, R.G., Erdey, M.D., Bretz, C.K., Manson, M.W., Sliter, R.W., Ross, S.L., Dieter, B.E., and Chin, J.L. 

(G.R. Cochrane and S.A. Cochran, eds.), California State Waters Map Series—Offshore of San Gregorio, California: U.S. Geological 

Survey Scientific Investigations Map 3306, pamphlet 38 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/sim3306.

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3306

EXPLANATION

Approximate modern shoreline—Defined as

Mean High Water (MHW) (+1.46 m), North

American Vertical Datum of 1988 (NAVD 88)

! Video observation

# Sample locality

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

Bathymetric contours—Derived from modified

2-m-resolution bathymetry grid. Contour

interval: 10 m

Habitat interpretation outline

122°30' 122°25'

37°20'

37°15'

Figure 1. Map showing video-observation locations and sample localities for Offshore of San Gregorio map 

area.

Kilometers 0 5 10

0 5 10Nautical Miles

122°40' 122°20'

38°

37°40'

37°20'

San

Francisco

Bay

San

Francisco

Area of

Map

Limit of California’s

State Waters

CALIF.

MAP LOCATION

10

Shd_c/d

Sme_c/u

Ss(s/g)h/w_r/s/u

Ss(s/g)_u

Ss(s)_r/u

DESCRIPTION OF MAP UNITS

UNCONSOLIDATED CONTINENTAL SHELF SEDIMENTS

Soft, unconsolidated, rippled sediment (sand)

Soft, unconsolidated sediment (sand and gravel), on flat shelf

Soft, mobile sediment window that has unconsolidated, hummocky, and rippled sediment waves, overlying scoured lag pavement 

of sand and gravel (sorted bedforms)

MIXED SUBSTRATE ON CONTINENTAL SHELF

Mixed habitat of soft, unconsolidated sediment, overlying hard, consolidated sedimentary bedrock

HARD SUBSTRATE ON CONTINENTAL SHELF

Deformed and differentially eroded, consolidated sedimentary-bedrock outcrop

EXPLANATION OF MAP SYMBOLS

Contact

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 map shows “potential” marine benthic habitats in the Offshore of San Gregorio map area. Marine benthic habitats represent a particular type of 

substrate, geomorphology, seafloor process, or any other attribute that may provide a habitat for a specific species or an assemblage of organisms. Such 

maps are based largely on seafloor geology, and this map integrates seafloor geology (sheet 10) with information depicted on several other thematic maps 

of the Offshore of San Gregorio map area: high-resolution bathymetry (sheet 1); shaded-relief imagery (sheet 2); backscatter (sheet 3); seafloor character 

(sheet 5); and ground-truth information (sheet 6). This map also uses information from the usSEABED bottom-sampling compilation by Reid and others 

(2006). The combination of remotely observed data (for example, multibeam bathymetry and backscatter, seismic-reflection profiles) and directly observed 

data (for example, camera transects, sediment samples) translates to higher confidence in the ability to interpret broad areas of the seafloor. 

To avoid any possible misunderstanding of the term “habitat,” the term “potential habitat” (as defined by Greene and others, 2005) is used herein to 

describe a set of distinct seafloor conditions that in the future may qualify as an “actual habitat.” Once habitat associations of a species are determined, they 

can be used to create maps that depict actual habitats, which then need to be confirmed by “ground-truth” surveying using in situ observations, video, and 

(or) photographic documentation. 

Marine benthic habitats are classified using the Benthic Marine Potential Habitat Classification Scheme, a mapping-attribute code developed by 

Greene and others (1999, 2007). In this map series, habitat-classification codes are based on the deepwater habitat-characterization scheme developed by 

Greene and others (1999), which was created to not only easily distinguish marine benthic habitats but also to facilitate ease of use and queries within GIS 

and database programs. The code, which is summarized in chapter 6 in the accompanying pamphlet, is derived from several categories of the Benthic 

Marine Potential Habitat Classification Scheme (Greene and others, 1999, 2007), and it can be subdivided on the basis of the spatial scale of the data. 

High-resolution, multibeam-sonar data, converted to bathymetric depth grids (seafloor digital elevation models; sheet 1), are essential to development 

of the habitat map, as is shaded-relief imagery (sheet 2), which allows for visualization of seafloor terrain and provides a foundation for interpretation of 

submarine landforms. Areas of seafloor bedrock exposures are identified by their common sharp edges and high relative relief; these may be contiguous 

outcrops, isolated parts of outcrop protruding through sediment cover (pinnacles or knobs), or isolated boulders. 

Backscatter maps (sheet 3) also are essential for developing potential benthic habitat maps. High backscatter is further indication of “hard” bottom, 

consistent with interpretation as rock or coarse sediment. In many locations, areas within or around a rocky feature appear to be covered by a thin veneer of 

sediment, identified on the habitat map as “mixed” induration (in other words, containing both rock and sediment). Broad, generally smooth areas of 

seafloor that lack sharp and angular edge characteristics are mapped as “sediment” and are further defined by various sedimentary features such as 

erosional scours and depressions, as well as depositional features such as dunes, mounds, or sand waves. Low backscatter, indicative of a “soft” bottom, 

also significantly aids identification and classification of sedimentary habitats.

The Offshore of San Gregorio map area lies in an area of roughly north-south-trending, fairly straight coastline that extends from south of Half Moon 

Bay (north of the map area) to Pigeon Point (south of the map area); this part of the coast is open to the full force of the Pacific Ocean. Delineated on the 

map are five potential marine benthic habitat types, all of which are located on the continental shelf (“Shelf” megahabitat). The meso- and macrohabitats 

include “hard” deformed sedimentary-bedrock outcrops; a hard-soft “mixed” habitat type made up of flat, hard bedrock locally covered with soft, unconsolidated sediment; and dynamic features such as mobile sand sheets and associated scour depressions. 

Most of the offshore part of the San Gregorio map area is located on the relatively flat and eroded continental shelf. Backscatter data show that the 

map area is dominated by “soft” sediment; however, the highly deformed and differentially eroded bedrock outcrops and their seafloor relief present the 

most spectacular backscatter imagery in this map area. These differentially eroded bedrock areas form the local relief and rugosity that make promising 

potential habitats for rockfish (Sebastes spp.). Sediment transport is primarily to the southeast, and sedimentary processes, which are quite active in the 

map area, produce the dynamic bedforms (primarily located along the periphery of hard bedrock exposures in the west-central part of the map area) that 

may be habitats for forage fish such as Pacific sand lance (Ammodytes hexapterus). In addition, erosion through shelf sediments down to a coarser lag has 

produced sediment-filled scour depressions that resemble “ripple scour depressions” of Cacchione and others (1984) and Phillips and others (2007), found 

mainly on the shelf in the northwestern and central parts of the map area.

Of the 107.75 km2

 in the map area, 14.44 km2 (13.4 percent) is exposed hard bedrock, and 1.18 km2 (1.1 percent) consists of sediment-covered 

bedrock, which is of the mixed hard-soft induration class. Soft, unconsolidated sediment covers a total of 92.13 km2 (85.5 percent) in the map area.

REFERENCES CITED

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.

Greene, H.G., Bizzarro, J.J., O’Connell, V.M., and Brylinsky, C.K., 2007, Construction of digital potential marine benthic habitat maps using a coded 

classification scheme and its application, in Todd, B.J., and Greene, H.G., eds., Mapping the seafloor for habitat characterization: Geological 

Association of Canada Special Paper 47, p. 141–155. 

Greene, H.G., Bizzarro, J.J., Tilden, J.E., Lopez, H.L., and Erdey, M.D., 2005, The benefits and pitfalls of geographic information systems in marine 

benthic habitat mapping, in Wright, D.J., and Scholz, A.J., eds., Place matters: Portland, Oregon State University Press, p. 34–46.

Greene, H.G., Yoklavich, M.M., Starr, R.M., O’Connell, V.M., Wakefield, W.W., Sullivan, D.E., McRea, J.E., and Cailliet, G.M., 1999, A classification 

scheme for deep seafloor habitats: Oceanologica Acta, v. 22, p. 663–678.

Phillips, E.L., Storlazzi, C.D., Dartnell, P., and Edwards, B.D., 2007, Exploring rippled scour depressions offshore Huntington Beach, CA: Coastal 

Sediments 2007, v. 3, p. 1,851–1,864.

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/.

1

Moss Landing Marine Laboratories, Center for Habitat Studies;

2

U.S. Geological Survey 

Potential Marine Benthic Habitats, Offshore of San Gregorio Map Area, California

By

Charles A. Endris,1 H. Gary Greene,1 Bryan E. Dieter,1 and Mercedes D. Erdey2

2014

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, 2014

MAGNETIC NORTH

13 / ° 1 2

TRUE NORTH

Onshore elevation data collected by Photoscience in 2005 for U.S. 

Geological Survey and County of San Mateo. California's State 

Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

Potential marine benthic habitats mapped by Charles A. Endris and 

H. Gary Greene, 2011. Bathymetric contours by Carrie K. Bretz, 2008

GIS database and digital cartography by Charles A. Endris and 

Mercedes D. Erdey

Edited by Taryn A. Lindquist

Manuscript approved for publication June 30, 2014

20

10

30

30

30

30

40

40

50

60

Ss(s)_r/u

Shd_c/d

Shd_c/d

Ss(s/g)_u

Shd_c/d

Shd_c/d

Shd_c/d

Shd_c/d

Sme_c/u

Shd_c/d

Shd_c/d

Sme_c/u

Shd_c/d

Shd_c/d

Sme_c/u

Sme_c/u

Shd_c/d

Sme_c/u

Shd_c/d

Ss(s/g)h/w_r/s/u

Ss(s/g)h/w_r/s/u

Ss(s/g)h/w_r/s/u

Sme_c/u Ss(s/g)_u

Sme_c/u

Shd_c/d

Sme_c/u

Ss(s/g)h/w_r/s/u

Shd_c/d

Ss(s)_r/u

Shd_c/d

Ss(s/g)h/w_r/s/u

Sme_c/u

Sme_c/u

Sme_c/u

Sme_c/u

Sme_c/u

Sme_c/u

Shd_c/d

Shd_c/d

Shd_c/d

Shd_c/d

Sme_c/u

Shd_c/d

Sme_c/u

Ss(s)_r/u

122°25'

122°25'

122°30'

122°30'

37°20'

37°20'

37°15'

37°15'

Shd_c/d

Shd_c/d

Shd_c/d

Sme_c/u

Shd_c/d

Shd_c/d

Sme_c/u

Ss(s)_r/u

Sme_c/u

Scientific Investigations Map 3306

Sheet 7 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey