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: Dartnell, P., 2014, Data integration and visualization, Offshore of Half Moon Bay map area, California, sheet 4 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

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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. These data are used by researchers to develop maps, reports, and other tools 

to assist in the coastal and marine spatial-planning capability of coastal-zone managers and 

other stakeholders. Seafloor-character, 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 Half Moon Bay map area. 

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

map of the Offshore of Half Moon Bay map area (see sheet 1 of this report). Numbered arrows 

show viewing directions of the perspective views on this sheet (figs. 1, 2, 4, 5, 6, 7); the 

numbers indicate the figure number of the perspective view.

The perspective views and bathymetric profiles in figures 1, 2, 5, 6, and 7 show the 

colored shaded-relief bathymetry of the Offshore of Half Moon Bay map area, as viewed from 

different directions. These views show a few examples of the complexity of the differentially 

eroded bedrock in the nearshore environment.

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. 7), which combine the bathymetry with seismic-reflection-profile 

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

the surface and subsurface.

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]

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

Data Integration and Visualization, Offshore of Half Moon Bay Map Area, California

By

Peter Dartnell

2014

Perspective views by Peter Dartnell, 2012. Bathymetric profiles in figures 2 and 6 by Peter Dartnell, 2012. Video-mosaic image in figure 3 by Peter Dartnell, 2012, 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. Seismic-reflection profile in figure 7 from sheet 8, this report 

GIS database and digital cartography by Nadine Golden and Florence L. Wong 

Manuscript approved for publication October 2, 2014

Onshore imagery from digital orthophotographs available at 

Cal-Atlas Geospatial Clearinghouse, http://atlas.ca.gov/ (last 

accessed January 2013). Offshore shaded-relief bathymetry from 

map on sheet 1, this report

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

Map view. Colored shaded-relief bathymetry map of 

Offshore of Half Moon Bay map area, generated from 

multibeam echosounder data. Colors show depth: 

reds and oranges indicate shallower areas; light 

blues, deeper areas. Illumination azimuth is 300°, 

from 45° above horizon. Numbered arrows show 

viewing directions of perspective views shown on 

this sheet; numbers correspond to figure numbers of 

views. 

Pillar Point

Mavericks

surf break

Pillar Point

Harbor

Figure 7. Perspective views to northeast over shelf offshore of city of Half Moon Bay. A, Perspective view of seafloor, revealing complex pattern of low-relief 

outcrop. Northwest-southeast-trending elliptical structure (c) can be seen in foreground. Black line shows location of seismic-reflection profile in B below. B, 

Same perspective view as A, converted to block diagram that combines bathymetry with northwest-southeast-trending seismic-reflection profile SU–719 

collected by USGS in 1997 (survey J–1–97–MB). Profile reveals syncline structure composed of Holocene marine nearshore shelf deposits and Miocene and 

Pliocene Purisima Formation (see sheet 10). Dashed blue lines highlight boundaries of separate geologic units in subsurface. Dashed yellow line is seafloor 

multiple (echo of seafloor reflector). Vertical exaggeration of perspective views, 2x; distance across bottom of view A, about 1.6 km.

Pillar Point Half Moon Bay

B

Pillar Point Half Moon Bay

A

c

Figure 6. Perspective view to south along San Mateo County coast, showing differentially eroded bedrock that trends north-south then bends to 

southeast (to left) toward coastline. Bathymetric profile B–B’ shows slight westward (to right) dip of bedrock; multibeam bathymetry and 

ground-truth-survey video and photographs confirm that bedrock protrudes between 1 and 4 m above sediment-filled troughs. Vertical exaggeration of 

perspective view, 2x; distance across bottom of image, about 1.8 km; vertical exaggeration of profile B–B’, about 10x.

B B’

Distance (m)

Depth (m)

0 100 200 300 400 500 600 700 800 900 1000

28

26

30

32

34

B B’

Figure 5. Perspective view to northwest south of Pillar Point Harbor. Differentially eroded bedrock, which trends to northwest at bottom (south end) of image, 

bends to west offshore of Pillar Point. White lines outline channel possibly cut by paleostream that flowed during times of lower sea level. Vertical exaggeration of 

perspective view, 2x; distance across bottom of image, about 900 meters.

Pillar Point Harbor

Pillar Point 

Figure 4. Perspective view to northeast offshore of southern part of Half Moon Bay, showing acoustic-backscatter imagery. In acoustic-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. Irregularly shaped areas of higher backscatter intensity (a) in foreground are depressions less than 

1 m deep that ground-truth-survey video and photographs show are composed of coarser grained sand and gravel; backscatter intensity of sand and gravel 

typically is higher than that of low-relief (0.5 m) rock outcrop (b) to east. Vertical exaggeration, 2x; distance across bottom of image, about 1.8 km.

Half Moon Bay

a

a

a

b

Figure 3. Video mosaic of area offshore of 

southern part of Half Moon Bay (see fig. 1 

for location), showing (west to east, from 

bottom to top) bedrock outcrop, then sharp 

vertical offset, and then coarser sand, 

sand ripples, and some shell material. 

Vertical offset may be linear scarp shown 

in figure 1. 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.

bedrock

 ~1-m vertical offset

- sand

- sand ripples

- shell material

Figure 2. Perspective view to northwest toward Mavericks surf break offshore of Pillar Point, showing spectacular folds exposed in bedrock west of Pillar Point. 

Bathymetric profile A–A’ shows shallowing “ramp” under surf break. Water depths range from about 35 m at west (left) end of profile to less than 5 m at east (right) end of 

profile. Long-period swells initiated from North Pacific storms interact with ramp, along with deeper channel to south, to generate one of largest surfing waves in world. 

Vertical exaggeration of perspective view, 2x; distance across bottom of image, about 1.6 km; vertical exaggeration of profile A–A’, 10x.

A A’

Distance (m)

Depth (m)

20

10

30

15

25

5

0 200 400 600 800 1000 1200 1400 1600

A’ A

Pillar Point

Figure 1. Perspective view to northwest over southern part of Half Moon Bay, 

showing lower relief areas of outcrop and also linear scarp possibly formed by 

east strand of San Gregorio Fault. Scarp has offset of 1 to 1.5 m, with west side 

higher than east side. Thin yellow line shows path of camera sled, towed 1 to 2 m 

over seafloor, that captured video and photographs; yellow arrow shows tow 

direction. Yellow rectangle shows location of video mosaic (fig. 3) generated from 

video captured over scarp. Vertical exaggeration, 2x; distance across bottom of 

image, about 600 m.

scarp

Pillar Point

2

7

6

4

1

5

Open-File Report 2014–1214

Sheet 4 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey