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: Dartnell, P., and Kvitek, R.G., 2015, Shaded-relief bathymetry, Offshore of Tomales Point map area, California, 

sheet 2 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

Figure 1. Map showing areas of multibeam-echosounder and bathymetric-sidescan surveys (pink 

shading) and topographic-lidar surveys (yellow shading). Also shown are data-collecting agencies 

(CSUMB, California State University, Monterey Bay, Seafloor Mapping Lab; FP, Fugro Pelagos; USGS, 

U.S. Geological Survey) and dates of surveys. Yellow line shows limit of California’s State Waters.

FP, 2007

 CSUMB, 

2007–2010

 USGS,

 2004–2005

38°15'

123°5' 123° 122°55'

38°10'

Limit of California’s 

 State Waters

10

DISCUSSION

This shaded-relief bathymetry map of the Offshore of Tomales Point map area in northern California was 

generated from bathymetry data collected by Fugro Pelagos, by California State University, Monterey Bay 

(CSUMB), and by the U.S. Geological Survey (USGS) (fig. 1). Mapping was completed between 2004 and 

2010, using a combination of 200-kHz and 400-kHz Reson 7125 and 244-kHz Reson 8101 multibeam 

echosounders, as well as 234-kHz and 468-kHz SEA SWATHplus bathymetric sidescan-sonar systems. These 

mapping missions combined to collect bathymetry from about the 10-m isobath to beyond the 3-nautical-mile 

limit of California’s State Waters.

During the Fugro Pelagos and CSUMB mapping missions, an Applanix POS MV (Position and Orientation System for Marine Vessels) was used to accurately position the vessel during data collection, and it also 

accounted for vessel motion such as heave, pitch, and roll (position accuracy, ±2 m; pitch, roll, and heading 

accuracy, ±0.02°; heave accuracy, ±5%, or 5 cm). KGPS altitude data (Fugro Pelagos, StarFix HP & XP units; 

CSUMB, NavCom 2050) were used to account for tidal-cycle fluctuations, and sound-velocity profiles were 

collected with an Applied Microsystems (AM) SVPlus sound velocimeter. Soundings were corrected for 

vessel motion using the Applanix POS MV data, for variations in water-column sound velocity using the AM 

SVPlus data, and for variations in water height (tides) using vertical-position data from the KGPS receivers.

For the USGS mapping missions within Tomales Bay (Anima and others, 2008), differential GPS 

(DGPS) data were combined with measurements of vessel motion (heave, pitch, and roll) in a CodaOctopus 

F180 attitude-and-position system to produce a high-precision vessel-attitude packet. This packet was transmitted to the acquisition software in real time and combined with instantaneous sound-velocity measurements 

at the transducer head before each ping. The returned samples were projected to the seafloor using a 

ray-tracing algorithm that works with previously measured sound-velocity profiles. Statistical filters were 

applied to the raw samples that discriminate the seafloor returns (soundings) from unintended targets in the 

water column.

Processed soundings were exported from the acquisition and processing software as XYZ files and 

bathymetric surface models. Once all of the surface models were transformed to a common projection and 

datum, they were merged together into one overall 2-m resolution bathymetric-surface model and clipped to 

the boundary of the map area. An illumination having an azimuth of 300° and from 45° above the horizon was 

then applied to the bathymetric surface to create the shaded-relief imagery. Note that the ripple patterns and 

parallel lines that are apparent within the map area are data-collection and processing artifacts. In addition, 

lines at the borders of some surveys are the result of slight differences in depth as measured by different 

mapping systems in different years. These various artifacts are made obvious by the hillshading process. 

Bathymetric contours were generated at 10-m intervals from a modified 2-m-resolution bathymetric 

surface. The original surface was smoothed using the Focal Mean tool in ArcGIS and a circular neighborhood 

with a radius of 20 to 30 m (depending on the area). The contours were generated from this smoothed surface 

using the ArcGIS Spatial Analyst Contour tool. The most continuous contour segments were preserved; 

smaller segments and isolated island polygons were excluded from the final output. 

The onshore-area image was generated by applying the same illumination (azimuth of 300° and from 45° 

above the horizon) to 2- and 3-m-resolution topographic-lidar data available from NOAA Coastal Service 

Center’s Digital Coast and the U.S. Geological Survey, National Elevation Dataset (available at 

http://ned.usgs.gov/).

REFERENCE CITED

Anima, R.J., Chin, J.L., Finlayson, D.P., McGann, M.L., and Wong, F.L., 2008, Interferometric sidescan 

bathymetry, sediment and foraminiferal analyses; a new look at Tomales Bay, California: U.S. Geological 

Survey Open-File Report 2008–1237, 33 p., available at http://pubs.usgs.gov/of/2008/1237/.

EXPLANATION

Amount of illumination

Illuminated (facing false sun)

In shadow (facing away from false sun)

Direction of illumination from false sun—Position of false sun is at 300° azimuth, 45° above 

horizon [arrow included in explanation for illustration purposes only; not shown on map]

 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 2-m-resolution bathymetry grid. Contour 

interval: 10 m

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

1

U.S. Geological Survey; 

2

California State University Monterey Bay, Seafloor Mapping Lab

Shaded-Relief Bathymetry, Offshore of Tomales Point Map Area, California

By

Peter Dartnell1 and Rikk G. Kvitek2

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

Shaded-relief bathymetry by Peter Dartnell, 2013 (data collected by Fugro Pelagos in 2007, by 

California State University, Monterey Bay, Seafloor Mapping Lab in 2007–2010, and by U.S. Geological 

Survey in 2004–2005). Bathymetric contours by Mercedes D. Erdey, 2013

GIS database and digital cartography by Nadine E. Golden

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

10

20

40

30

50

60

70

10

10

10

10

10

10

Tomales Point

 Point Reyes

National Seashore

Tomales Bay

Bodega 

 Bay

Toms

Point Keys Creek

Abbots

Lagoon

123°5' 123° 122°55'

38°15'

38°10' 38°10'

38°15'

123°5' 123° 122°55'

Open-File Report 2015–1088

Sheet 2 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey