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: Bretz, C.K., Kvitek, R.G., Dartnell, P., and Phillips, E.L., 2014, Colored shaded-relief bathymetry, Offshore of San 

Gregorio map area, California, sheet 1 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

CSUMB, 2007

FP, 

2006, 2007

San Gregorio

State Beach

 Pescadero

State Beach

122°30'

37°20'

122°25'

37°15'

Figure 1. Map showing areas of multibeam-echosounder surveys (pink shading) and onshore topographiclidar surveys (yellow shading). Also shown are data-collecting agencies (CSUMB, California State University, 

Monterey Bay, Seafloor Mapping Lab; FP, Fugro Pelagos) and dates of surveys if known.

Photoscience,

2005

10

50

20

10

40

60

30

DISCUSSION

This colored shaded-relief bathymetry map of the Offshore of San Gregorio map area in northern 

California was generated from bathymetry data collected by Fugro Pelagos and by California State University, 

Monterey Bay (CSUMB) (fig. 1). Mapping was completed in 2006 and 2007, using a combination of 400-kHz 

Reson 7125 and 244-kHz Reson 8101 multibeam echosounders. These mapping missions combined to collect 

bathymetry data from about the 10-m isobath to beyond the 3-nautical-mile limit of California’s State Waters.

During all the mapping missions, an Applanix POS MV (Position and Orientation System for Marine 

Vessels) was used to accurately position the vessels 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). To account for tidal-cycle fluctuations, CSUMB used NavCom 2050 GPS receiver 

(CNAV) data, and Fugro Pelagos used KGPS data (GPS data with real-time kinematic corrections); in 

addition, 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 watercolumn sound velocity using the AM SVPlus data, and for variations in water height (tides) using 

vertical-position data from the KGPS receivers. 

Processed soundings from the different mapping missions were exported from the acquisition or processing 

software as XYZ files and bathymetric surfaces. All the surfaces were merged 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. In addition, a modified “rainbow” color ramp was applied to the bathymetry data, using reds and 

oranges to represent shallower depths, and blues to represent greater depths (note that the Offshore of San 

Gregorio map area requires only the shallower part of the full-rainbow color ramp used on some of the other 

maps in the California State Waters Map Series; see, for example, Kvitek and others, 2012). This colored 

bathymetry surface was draped over the shaded-relief imagery at 60-percent transparency to create this colored 

shaded-relief map. Gray areas in map are gaps in data.

Bathymetric contours were generated at 10-m intervals from the merged 2-m-resolution bathymetric 

surface. The most continuous contour segments were preserved; smaller segments and isolated island polygons 

were excluded from the final output. Contours were smoothed using a polynomial approximation with 

exponential kernel algorithm and a tolerance value of 60 m.

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

above the horizon) to 1-m-resolution topographic-lidar data collected by Photoscience in 2005 for the U.S. 

Geological Survey and the County of San Mateo.

REFERENCE CITED

Kvitek, R.G., Phillips, E.L., and Dartnell, P., 2012, Colored shaded-relief bathymetry, Hueneme Canyon and 

vicinity, California, sheet 1 in Johnson, S.Y., Dartnell, P., Cochrane, G.R., Golden, N.E., Phillips, E.L., 

Ritchie, A.C., Kvitek, R.G., Greene, H.G., Krigsman, L.M., Endris, C.A., Clahan, K.B., Sliter, R.W., 

Wong, F.L., Yoklavich, M.M., and Normark, W.R. (S.Y. Johnson, ed.), California State Waters Map 

Series—Hueneme Canyon and vicinity, California: U.S. Geological Survey Scientific Investigations Map 

3225, pamphlet 41 p., 12 sheets, available at http://pubs.usgs.gov/sim/3225/.

EXPLANATION

Depth (in meters) and illumination (bright areas are illuminated, facing false sun; dark areas 

are in shadow, facing away from false sun) 

Shallow

Deep

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 modified 2-m-resolution bathymetry grid. 

Contour interval: 10 m

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

1

California State University, Monterey Bay, Seafloor Mapping Lab;

2

U.S. Geological Survey 

Colored Shaded-Relief Bathymetry, Offshore of San Gregorio Map Area, California

By

Carrie K. Bretz,1 Rikk G. Kvitek,1 Peter Dartnell,2 and Eleyne L. Phillips2

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

Shaded-relief bathymetry by Peter Dartnell, 2012 (data collected by Fugro Pelagos in 2006 and 2007 and by 

California State University, Monterey Bay, Seafloor Mapping Lab in 2007). Bathymetric contours by Carrie K. 

Bretz, 2008

GIS database and digital cartography by Nadine E. Golden

Edited by Taryn A. Lindquist

Manuscript approved for publication June 30, 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

10

20

30

30

30

30

40

40

50

60

San Gregorio

 State Beach

 Pescadero

 State Beach

122°30' 122°25'

122°30' 122°25'

37°20'

37°15'

37°20'

37°15'

Scientific Investigations Map 3306

Sheet 1 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey