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/ofr20151088 or http://pubs.usgs.gov/of/2015/1088/

Suggested Citation: Endris, C.A., Greene, H.G., Dieter, B.E., Lowe, E.N., and Erdey, M.D., 2015, Potential marine benthic habitats, 

Offshore of Tomales Point map area, California, sheet 7 in Johnson, S.Y., Dartnell, P., Golden, N.E., Hartwell, S.R., Greene, H.G., Erdey, 

M.D., Cochrane, G.R., Watt, J.T., Kvitek, R.G., Manson, M.W., Endris, C.A., Dieter, B.E., Krigsman, L.M., Sliter, R.W., Lowe, E.N., and 

Chin, J.L. (S.Y. Johnson and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Tomales Point, California: U.S. 

Geological Survey Open-File Report 2015–1088, pamphlet 38 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20151088.

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151088

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Figure 1. Map showing video-observation locations and sample localities for Offshore of Tomales Point 

map area.

EXPLANATION

3-nautical-mile limit of California's 

State Waters

Approximate modern shoreline

—Defined as Mean High Water 

(MHW) (+1.33 m), North

American Vertical Datum of 

1988 (NAVD 1988)

Video observation

Sample locality

Habitat interpretation outline

Bathymetric contours—Derived 

from modified 10-m-resolution 

bathymetry grid. Contour 

interval: 10m

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123°20 123°

38°20'

38°

0 5 10 Kilometers

0 5 10 Nautical Miles

Area of

Map

Limit of California’s

State Waters

Point Reyes

Tomales Bay

Bodega

Bay

CALIF.

MAP LOCATION

Bodega

Harbor

10

Es(s)h_s/u

Es(s)b/m_u

Es(s)w_r/s/u

Esh_u

Eme_g/uh

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Shm_a?

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DESCRIPTION OF MAP UNITS

UNCONSOLIDATED CONTINENTAL SHELF SEDIMENTS

Soft, unconsolidated sediment (sand and mud), predominantly rippled 

Depression in soft, unconsolidated sediment (sand and mud)

Unconsolidated dynamic mound of sediment (sand and mud)

Soft, unconsolidated sediment (sand), predominantly rippled 

Sediment waves in soft, unconsolidated, rippled sediment (sand)

Rippled scour depressions (sand and gravel)

MIXED SUBSTRATE ON CONTINENTAL SHELF

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

sedimentary bedrock

Mixed habitat of soft, unconsolidated sediment, overlying hard, granitic bedrock

HARD SUBSTRATE ON CONTINENTAL SHELF

Bedrock outcrop of hard granitic rock

Faulted, fractured, deformed, and differentially eroded sedimentary bedrock

Boulder or pinnacle of hard granitic rock

Boulder or pinnacle of hard sedimentary bedrock

ANTHROPOGENIC FEATURES ON CONTINENTAL SHELF

Hard mounds comprised of unidentified material, possibly marine debris (inferred)

UNCONSOLIDATED ESTUARY SEDIMENTS

Soft, unconsolidated sediment, predominantly rippled (sand and mud)

Soft, unconsolidated, hummocky sediment (sand and mud)

Depression in soft, unconsolidated sediment (sand and mud)

Mound in soft, unconsolidated sediment (sand and mud)

Soft, unconsolidated sediment, predominantly rippled (sand)

Current-scoured depression in soft, unconsolidated sediment (sand)

Shoreline mound, or relic beach, composed of soft, unconsolidated sediment (sand)

Sediment waves and ripples in current-scoured soft, unconsolidated sediment (sand)

Depression in soft, unconsolidated sediment

MIXED SUBSTRATE IN ESTUARY

Mixed habitat of soft, unconsolidated sediment overlying hard granitic bedrock

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 10-m-resolution bathymetry grids. Contour interval: 10 m 

DISCUSSION

This map shows “potential” marine benthic habitats in the Offshore of Tomales Point 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 Tomales Point 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. Shaded-relief imagery (sheet 2) allows for 

visualization of seafloor terrain, providing 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. 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 the 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 Tomales Point map area contains 23 potential marine benthic habitat types, covering 126.97 

km2

 from the interpreted data. These habitat types include unconsolidated continental shelf sediments (6 habitat 

types), mixed substrate on the continental shelf (2 habitat types), hard substrate on the continental shelf (4 habitat 

types), possible anthropogenic features on the continental shelf (1 habitat type), unconsolidated estuary sediments 

(9 habitat types), and mixed substrate in the estuary (1 habitat type). The habitat types mapped on the shelf cover 

an area of 117.22 km2 (92.3 percent) while those in the estuary (Tomales Bay) cover 9.75 km2 (7.7 percent). In 

the total area mapped, the dominant habitat type was soft unconsolidated sediment that covered 85.30 km2 (67.2 

percent) with hard rock covering 37.34 km2

 (29.4 percent), sediment covered bedrock covering 4.21 km2 (3.3 

percent), and hard unidentified anthropogenic features, possibly related to marine debris, covering 0.13 km2 (0.1 

percent). 

Rock outcrops and rubble are considered the primary habitat type for rockfish and lingcod (Cass and others, 

1990; Love and others, 2002), both recreationally and commercially important species. Dynamic bedforms such 

as sand waves are considered potential foraging habitat for juvenile lingcod (Ophiodon elongatus) and possibly 

migratory fishes (Beaudreau, 2005), as well as for forage fish such as Pacific sand lance.

REFERENCES CITED

Beaudreau, A., 2005, Diet and prey size spectrum of lingcod (Ophiodon elongates), a top predator in rock reefs 

of the San Juan Archipelago, in 2005 Puget Sound Georgia Basin Research Conference, Abstracts and 

Biographies: Seattle, Washington, p. 47.

Cass, A.J., Beamish, R.J., and McFarlane, G.A., 1990, Lingcod (Ophiodon elongates): Canadian Journal of 

Fisheries and Aquatic Sciences, Special Publication 109, 40 p.

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.

Love, M.S., Yoklavich, M., Thorsteinson, L., and Butler, J. 2002, The rockfishes of the northeast Pacific: 

University of California Press, Berkeley, p. 405, doi:10.5860/CHOICE.40-3403.

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 Tomales Point Map Area, California

By

Charles A. Endris,1 H. Gary Greene,1 Bryan E. Dieter,1 Erik N. Lowe,2 and Mercedes D. Erdey2

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

14°

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2015

MAGNETIC 

 NORTH

TRUE NORTH

Potential marine benthic habitats mapped by H. Gary 

Greene, Charles A. Endris and Bryan E. Dieter, 2012–2013. 

Bathymetric contours by Mercedes D. Erdey, 2013

GIS database and digital cartography by Charles A. 

Endris and Erik N. Lowe

Manuscript approved for publication May 4, 2015

Onshore elevation data from California Coastal Conservancy, 

available at http://www.csc.noaa.gov/digitalcoast/data/

coastallidar/, and from U.S. Geological Survey, 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 10N

NOT INTENDED FOR NAVIGATIONAL USE

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Tomales Point

Tomales Bay

 Point Reyes

National Seashore

Elephant Rock

Dillon Beach

123°5' 123° 122°55'

123°5' 123° 122°55'

38°15'

38°10'

38°15'

38°10'

Open-File Report 2015–1088

Sheet 7 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey