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., 2015, Data integration and visualization, Offshore of Tomales Point map area, California, sheet 4 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

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

20

30

40

50

60

70

10

DISCUSSION

Mapping California’s State Waters has produced a vast amount of acoustic and visual 

data, including bathymetry, acoustic backscatter, seismic-reflection profiles, and seafloor video 

and photography. Researchers use these data to develop maps, reports, and other tools to assist 

coastal-zone managers and other stakeholders in coastal and marine spatial-planning. Seafloorcharacter, habitat, and geologic maps may be used for fisheries management, for designation 

of Marine Protected Areas, for monitoring of environmental change such as sea-level-rise 

impacts, for prediction of sediment and contaminant budgets and transport, and for assessment 

of earthquake and tsunami hazards. To achieve these goals, it is helpful to integrate the 

different datasets and then view the results in three-dimensional representations such as those 

displayed on this data integration and visualization sheet for the Offshore of Tomales Point 

map area.

The map view in the center of the sheet is similar to the colored shaded-relief bathymetry 

map of the Offshore of Tomales Point map area (see sheet 1 of this report). Numbered arrows 

show viewing directions of the perspective views on this sheet; the numbers indicate the figure 

number of the perspective view.

The perspective views and bathymetric profiles in figures 1, 2, 4, 5, and 6 show the 

colored shaded-relief bathymetry of the Offshore of Tomales Point map area, as viewed from 

different directions. These views highlight the diverse seafloor environments in this region 

including a featureless, sedimented seafloor interspersed with complex distributions of 

coarse-grained sediment, folded sedimentary rocks, and massive, fractured granite.

Video-mosaic images created from seafloor digital video (fig. 3) display the geologic 

(rock, sand, mud) and biologic complexity of the seafloor. Whereas photographs capture 

high-quality snapshots of a small area of the seafloor, video mosaics can capture larger areas 

and, thus, can show transitional zones between different seafloor environments.

Draping the acoustic-backscatter imagery (see sheet 3 of this report) over the bathymetry 

data (fig. 4) highlights the relations between the backscatter intensity and the seafloor 

morphology, and it also aids in seafloor habitat and geology interpretations.

Block diagrams (fig. 6), which combine the bathymetry with seismic-reflection-profile 

data (see sheet 8 of this report), help show the stratigraphic and structural relations between 

the surface and subsurface. 

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

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]

Data Integration and Visualization, Offshore of Tomales Point Map Area, California

By

Peter Dartnell

2015

Perspective views by Peter Dartnell, 2013. Video-mosaic image in figure 3 by Peter Dartnell, 2013, using software developed by Dr. Yuri Rzhanov, Center for Coastal and Ocean 

Mapping, University of New Hampshire, through joint U.S. Geological Survey–University of New Hampshire cooperative agreement. Acoustic-backscatter imagery in figure 4 from 

map on sheet 3, this report. Bathymetric profile in figure 5 by Peter Dartnell, 2013. Seismic-reflection profile in figure 6 from sheet 8, this report. 

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/. Offshore 

shaded-relief bathymetry from map on sheet 2, this report. 

California's State Waters limit from NOAA Office of Coast 

Survey

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

Map view. Colored shaded-relief bathymetry map of 

Offshore of Tomales Point map area, generated from 

multibeam-echosounder and bathymetric-sidescan 

data. Colors show depth: reds and oranges indicate 

shallower areas; blues, deeper areas. Illumination 

azimuth is 300°, from 45° above horizon. Note that 

ripple patterns and parallel lines apparent within map 

are data-collection and processing artifacts. Lines at 

some borders of surveys are created by slight 

differences in depth measured by different mapping 

systems during different years. Artifacts are made 

obvious by hillshading process. Numbered arrows 

show viewing directions of perspective views shown 

on this sheet, numbers correspond to figure numbers 

of view. Black line near arrow 6 shows location of 

seismic-reflection profile in figure 6.

 fig 6. seismic-reflection profile line

Tomales Point

Tomales Bay

 Point Reyes

National Seashore

Keys Creek

Bodega Bay

Toms 

Point

A

B

80 m

160 m

f

Figure 6. Perspective views to southeast over offshore region near Point Reyes National Seashore. A, perspective view of both featureless seafloor (f) and rougher seafloor of low-relief 

rock outcrop (g). Black line shows location of seismic-reflection profile in B below (also see map view). B, same view as A, converted to block diagram combining bathymetry with 

northeast-southwest trending seismic-reflection profile PR−76 (sheet 8, this report). Profile reveals syncline (h) below featureless seafloor, covered by very thin deposit of uppermost 

Pleistocene and Holocene sediment (blue shading) (sheets 8 and 9, this report). To northeast and southwest, dipping beds that reach seafloor (g) form low-relief rock outcrops. Dashed 

yellow line is seafloor multiple (echo of seafloor reflector). Vertical exaggeration of both views, 2x; distance across bottom of view A, 1.4 km; base of seismic-reflection profile is more than 

160 m across.

g g

g f g

h

Point Reyes National Seashore

Point Reyes National Seashore

Figure 5. Perspective view to northwest along Tomales Bay and bathymetric profile A-A’. Most of central Tomales Bay has smooth, flat seafloor, however, a few large 

depressions with up to 10-m of relief and steep sides are found offshore of land promontories. Sediment within Tomales Bay decreases in grain size from mouth of 

bay in north towards center of bay. Coarse- to medium-sand is found at mouth compared to fine- to very-fine sand in central bay (Anima and others, 2008). 

Northwest-striking San Andreas Fault extends up axis of Tomales Bay (sheet 10, this report). Vertical exaggeration of perspective view, 2x; distance across bottom, 

about 1 km; vertical exaggeration of Profile A-A’, 5x.

A A’ 12 slope °

12 slope °

Distance (m)

0 50 100 150 200 250 300 350 400

Depth (m) 10

6

8

12

14

16

A’

A

Tomales Bay

Figure 4. Perspective views to northeast of both colored shaded-relief bathymetry (A), and gray-scale acoustic backscatter (B). In backscatter imagery, lighter tones 

indicate stronger backscatter intensity suggesting rock or coarser grained sediment, whereas darker tones indicate weaker backscatter intensity suggesting finer 

grained sediment. Bathymetry shows wide distribution of rock outcrop with up to 3.5 m of relief (d). Backscatter imagery shows outcrops with high backscatter 

intensities; however, some regions of lower relief (e) also have high backscatter intensity and are likely composed of coarser sands and (or) or mixed rock (cobbles, 

boulders). Parallel lines of higher backscatter (B) are data-collection and processing artifacts. Vertical exaggeration of both views, 2x; distance across bottom of both 

views, about 3 km.

A

B

d

d

e

e

e

e

e

e

Point Reyes 

 National Seashore

Point Reyes 

 National Seashore

anenomes

sea stars

Figure 3. Video mosaic of area offshore of Point Reyes National Seashore, which 

shows transition from sandy seafloor to rock outcrop (see fig. 1 for location). 

Outcrop is relatively clean of encrusting organisms, algae, and kelp and has 

linear ridges perpendicular to path of camera sled. Outcrop appears to be 

layered sedimentary rock, consistent with overall morphology seen in figure 1. 

Numerous sea stars are found at transition from sand to rock. Camera sled tow 

direction is from bottom to top. Bright green dots within mosaic are from paired 

lasers on camera sled used to size objects on seafloor. Mosaic is comprised of 

about 30 seconds of video recorded as camera sled traveled above seafloor. 

Video mosaic created using software developed by Dr. Yuri Rzhanov, Center for 

Coastal and Ocean Mapping, University of New Hampshire, through joint U.S. 

Geological Survey–University of New Hampshire cooperative agreement. 

~1.8 m

layered sedimentary rock

sandy 

seafloor

camera sled paired lasers

east

west

Figure 2. Perspective view to south, down coast, past Tomales Point and into Tomales Bay. Massive granitic seafloor outcrop extends north and west from Tomales Point. Locally, 

outcrop has low relief (less than 4 m) but overall surface grades relatively steeply from shoreline to depth of about 60 m at transition to smooth, sediment-covered seafloor in a 

distance of only 3 km. Low-relief channel cut into granitic seafloor outcrops (c) that trends offshore north of Tomales Point probably served as sediment pathway for sediment moving 

out of Tomales Bay during lower sea levels. Vertical exaggeration of perspective view, 2x; distance across bottom, about 3 km.

c

Tomales

Point

Tomales 

 Bay

Figure 1. Perspective view to north along west flank of Point Reyes National Seashore. View highlights two distinct rock outcrop types; outcrops offshore (a) are linear, folded, 

west-dipping sedimentary rocks, while nearshore outcrops (b) comprise massive, disorganized and fractured granitic rocks. Thin yellow line shows path of camera sled (towed 1 

to 2 m above seafloor) that captured video and photographs. Yellow rectangle shows location of video mosaic (fig. 3) generated from video captured above linear 

sedimentary-rock outcrop. Yellow arrow shows towing direction of camera sled. Vertical exaggeration of perspective view, 2x; distance across bottom about 1.4 km.

a

b

depth

6

1

4

2

5

Open-File Report 2015–1088

Sheet 4 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey