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/of/2014/1214/

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

Moon Bay map area, California, sheet 7 in Cochrane, G.R., Dartnell, P., Greene, H.G., Johnson, S.Y., Golden, N.E., Hartwell, S.R., Dieter, 

B.E., Manson, M.W., Sliter, R.W., Ross, S.L., Watt, J.T., Endris, C.A., Kvitek, R.G., Phillips, E.L., Erdey, M.D., Chin, J.L., and Bretz, C.K. 

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

Survey Open-File Report 2014–1214, pamphlet 37 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20141214.

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141214

Figure 1. Map showing video-observation locations and sample localities for Offshore of Half Moon Bay map 

area.

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122°35' 122°30' 122°25'

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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

Kilometers 0 5 10

0 5 10Nautical Miles

122°40' 122°20'

38°

37°40'

37°20'

San

Francisco

Bay

Area of

Map

Limit of California’s

State Waters

CALIF.

MAP LOCATION

10

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DESCRIPTION OF MAP UNITS

UNCONSOLIDATED CONTINENTAL SHELF SEDIMENTS

Soft, unconsolidated sediment (sand), predominantly rippled

Soft, unconsolidated sediment (sand or gravel); inferred

Soft, unconsolidated, hummocky sediment (sand and gravel)

Soft, mobile sediment window that has unconsolidated and rippled sediment waves, 

overlying scoured lag pavement of sand and gravel (sorted bedforms)

MIXED SUBSTRATE ON CONTINENTAL SHELF

Mixed habitat of boulders or pinnacles and cobbles with soft, unconsolidated sediment

Mixed habitat of soft, unconsolidated sediment, locally overlying hard, consolidated 

sedimentary bedrock

HARD SUBSTRATE ON CONTINENTAL SHELF

Hard, granitic rock exposure; may contain unconsolidated sediment (sand) in crevices 

and cracks 

Hard, deformed, and differentially eroded sedimentary-bedrock outcrop

Hard, flat, deformed, and differentially eroded sedimentary-bedrock outcrop

ANTHROPOGENIC FEATURES

Soft, unconsolidated, anthropogenically deposited sediment (possible dredge spoils); 

inferred

Hard anthropogenic feature (groin or jetty)

EXPLANATION OF MAP SYMBOLS

Contact

Area of “no data”—Areas near shoreline not mapped owing to insufficient highresolution 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 Half Moon Bay 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 Half Moon Bay 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 (fig. 1). 

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 Half Moon Bay map area includes Half Moon Bay and the continental shelf to the north, 

west, and south of it. Delineated on the map area are 11 potential marine benthic habitat types, all of which are 

located on the continental shelf (“Shelf” megahabitat); two of these potential habitats are anthropogenic, found 

near the entrance to Pillar Point Harbor. The meso- and macrohabitats include deformed sedimentary-rock 

outcrops; flat, hard bedrock exposures; rugose, fractured granitic rock; and dynamic features such as mobile sand 

sheets, sand waves, and associated scour depressions. Backscatter data show that over one-half of the area is 

covered with “soft” sediment, although the highly deformed and differentially eroded bedrock outcrops and their 

seafloor relief present the most spectacular backscatter imagery in this map area.

Although the map area is located on the relatively flat, eroded continental shelf, the differentially eroded 

bedrock forms local relief and rugosity that make promising potential habitats for rockfish (Sebastes spp.). 

Sediment transport is primarily to the southeast, and sedimentary processes are quite active in the area, producing 

the dynamic bedforms 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 126.8 km2

 in the map area, 56.25 km2 (44.4 percent) is exposed hard bedrock, and 7.73 km2 (6.1 

percent) consists of sediment-covered bedrock, which is of the mixed hard-soft induration class. Soft, unconsolidated sediment covers a total of 70.5 km2

 (55.6 percent), and 62.77 km2 (49.5 percent) consists of mobile sand 

sheets, ripple scour depressions, and gravels. Anthropogenic habitats cover 0.05 km2 (0.04 percent) and are 

located in the vicinity of Pillar Point Harbor.

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 Half Moon Bay Map Area, California

By

Bryan E. Dieter,1 H. Gary Greene,1 Charles A. Endris,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

14°

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2014

MAGNETIC 

 NORTH

TRUE NORTH

Potential marine benthic habitats mapped by Bryan E. 

Dieter 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 

Manuscript approved for publication October 2, 2014

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

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122°25'

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Open-File Report 2014–1214

Sheet 7 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey