California State Waters Map Series—Offshore of Pigeon 

Point, California

By Guy R. Cochrane, Janet T. Watt, Peter Dartnell, H. Gary Greene, Mercedes D. Erdey, Bryan E. Dieter, Nadine 

E. Golden, Samuel Y. Johnson, Charles A. Endris, Stephen R. Hartwell, Rikk G. Kvitek, Clifton W. Davenport, Lisa 

M. Krigsman, Andrew C. Ritchie, Ray W. Sliter, David P. Finlayson, and Katherine L. Maier

(Guy R. Cochrane and Susan A. Cochran, editors)

Pamphlet to accompany

Open-File Report 2015–1232

2015

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit

http://www.usgs.gov/ or call 1–888–ASK–USGS (1–888–275–8747).

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod/. 

To order USGS information products, visit http://store.usgs.gov/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply

endorsement by the U.S. Government. 

Although this information product, for the most part, is in the public domain, it also may

contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items

must be secured from the copyright owner. 

Suggested citation:

Cochrane, G.R., Watt, J.T., Dartnell, P., Greene, H.G., Erdey, M.D., Dieter, B.E., Golden, N.E., Johnson, S.Y., 

Endris, C.A., Hartwell, S.R., Kvitek, R.G., Davenport, C.W., Krigsman, L.M., Ritchie, A.C., Sliter, R.W., Finlayson, 

D.P., and Maier, K.L. (G.R. Cochrane and S.A. Cochran, eds.), 2015, California State Waters Map Series—

Offshore of Pigeon Point, California: U.S. Geological Survey Open-File Report 2015–1232, pamphlet 40 p., 10 

sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20151232.

ISSN 2331-1258 (online)
iii

Contents

Preface...........................................................................................................................................................................1

Chapter 1. Introduction...................................................................................................................................................3

By Guy R. Cochrane

Regional Setting .........................................................................................................................................................3

Publication Summary..................................................................................................................................................5

Chapter 2. Bathymetry and Backscatter-Intensity Maps of the Offshore of Pigeon Point Map Area (Sheets 1, 2, and 

3)....................................................................................................................................................................................8

By Peter Dartnell and Rikk G. Kvitek

Chapter 3. Data Integration and Visualization for the Offshore of Pigeon Point Map Area (Sheet 4)...........................10

By Peter Dartnell

Chapter 4. Seafloor-Character Map of the Offshore of Pigeon Point Map Area (Sheet 5) ...........................................11

By Mercedes D. Erdey and Guy R. Cochrane

Chapter 5. Ground-Truth Studies for the Offshore of Pigeon Point Map Area (Sheet 6)..............................................16

By Nadine E. Golden and Guy R. Cochrane

Chapter 6. Potential Marine Benthic Habitats of the Offshore of Pigeon Point Map Area (Sheet 7).............................19

By H. Gary Greene and Charles A. Endris

Classifying Potential Marine Benthic Habitats ..........................................................................................................19

Examples of Attribute Coding ...................................................................................................................................21

Map Area Habitats....................................................................................................................................................21

Chapter 7. Subsurface Geology and Structure of the Offshore of Pigeon Point Map Area and the Pigeon Point to 

Southern Monterey Bay Region (Sheets 8 and 9)........................................................................................................22

By Janet T. Watt, Samuel Y. Johnson, and Stephen R. Hartwell

Data Acquisition........................................................................................................................................................22

Seismic-Reflection Imaging of the Continental Shelf................................................................................................22

Geologic Structure and Recent Deformation ............................................................................................................24

Thickness and Depth to Base of Uppermost Pleistocene and Holocene Deposits ...................................................24

Chapter 8. Geologic and Geomorphic Map of the Offshore of Pigeon Point Map Area (Sheet 10)..............................28

By Janet T. Watt, Stephen R. Hartwell, and Clifton W. Davenport

Geologic and Geomorphic Summary........................................................................................................................28

Description of Map Units ..........................................................................................................................................31

Offshore Geologic And Geomorphic Units ............................................................................................................31

Onshore Geologic and Geomorphic Units ............................................................................................................32

Acknowledgments........................................................................................................................................................34

References Cited .........................................................................................................................................................35

Figures

Figure 1–1. Physiography of Pigeon Point to southern Monterey Bay region and its environs...................................... 6

Figure 1–2. Coastal geography of Offshore of Pigeon Point map area.......................................................................... 7

Figure 4–1. Detailed view of ground-truth data, showing accuracy-assessment methodology.................................... 13

Figure 5–1. Photograph of camera sled used in USGS 2007 ground-truth survey ...................................................... 16

Figure 5–2. Graph showing distribution of primary and secondary substrate determined from video observations in 

Offshore of Pigeon Point map area .......................................................................................................... 18
iv

Tables

Table 4–1. Conversion table showing how video observations of primary substrate, secondary substrate, and 

abiotic seafloor complexity are grouped into seafloor-character-map Classes I, II, and III for use in 

supervised classification and accuracy assessment in Offshore of Pigeon Point map area ..................... 14

Table 4–2. Accuracy-assessment statistics for seafloor-character-map classifications in Offshore of Pigeon Point 

map area .................................................................................................................................................. 15

Table 7–1. Area, sediment-thickness, and sediment-volume data for California’s State Waters in Pigeon Point to 

southern Monterey Bay region, as well as in Offshore of Pigeon Point map area .................................... 27

Table 8–1. Areas and relative proportions of offshore geologic map units in Offshore of Pigeon Point map area...... 30

Map Sheets

Sheet 1. Colored Shaded-Relief Bathymetry, Offshore of Pigeon Point Map Area, California

By Peter Dartnell, Rikk G. Kvitek, Andrew C. Ritchie, and David P. Finlayson

Sheet 2. Shaded-Relief Bathymetry, Offshore of Pigeon Point Map Area, California 

By Peter Dartnell, Rikk G. Kvitek, Andrew C. Ritchie, and David P. Finlayson

Sheet 3. Acoustic Backscatter, Offshore of Pigeon Point Map Area, California 

By Peter Dartnell, Rikk G. Kvitek, Andrew C. Ritchie, and David P. Finlayson

Sheet 4. Data Integration and Visualization, Offshore of Pigeon Point Map Area, California 

By Peter Dartnell 

Sheet 5. Seafloor Character, Offshore of Pigeon Point Map Area, California 

By Mercedes D. Erdey and Guy R. Cochrane 

Sheet 6. Ground-Truth Studies, Offshore of Pigeon Point Map Area, California 

By Nadine E. Golden, Guy R. Cochrane, and Lisa M. Krigsman 

Sheet 7. Potential Marine Benthic Habitats, Offshore of Pigeon Point Map Area, California 

By Charles A. Endris, H. Gary Greene, Bryan E. Dieter, and Mercedes D. Erdey

Sheet 8. Seismic-Reflection Profiles, Offshore of Pigeon Point Map Area, California 

By Janet T. Watt, Samuel Y. Johnson, and Ray W. Sliter 

Sheet 9. Local (Offshore of Pigeon Point Map Area) and Regional (Offshore from Pigeon Point to Southern 

Monterey Bay) Shallow-Subsurface Geology and Structure, California 

By Janet T. Watt, Samuel Y. Johnson, Stephen R. Hartwell, Ray W. Sliter, and Katherine L. Maier

Sheet 10. Offshore and Onshore Geology and Geomorphology, Offshore of Pigeon Point Map Area, California 

By Janet T. Watt, Stephen R. Hartwell, and Clifton W. Davenport
1

California State Waters Map Series—Offshore of Pigeon 

Point, California

By Guy R. Cochrane,1 Janet T. Watt,1 Peter Dartnell,

1 H. Gary Greene,2 Mercedes D. Erdey,1 Bryan E. Dieter,2

Nadine E. Golden,1 Samuel Y. Johnson,1 Charles A. Endris,2 Stephen R. Hartwell,

1 Rikk G. Kvitek,3 Clifton W. 

Davenport,4 Lisa M. Krigsman,5 Andrew C. Ritchie,1 Ray W. Sliter,1 David P. Finlayson,1 and Katherine L. Maier1

(Guy R. Cochrane1 and Susan A. Cochran,1 editors)

Preface 

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping 

Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, 

marine benthic habitats, and geology within California’s State Waters. The program supports a large 

number of coastal-zone- and ocean-management issues, including the California Marine Life Protection 

Act (MLPA) (California Department of Fish and Wildlife, 2008), which requires information about the 

distribution of ecosystems as part of the design and proposal process for the establishment of Marine 

Protected Areas. A focus of CSMP is to map California’s State Waters with consistent methods at a 

consistent scale.

The CSMP approach is to create highly detailed seafloor maps through collection, integration, 

interpretation, and visualization of swath sonar bathymetric data (the undersea equivalent of satellite 

remote-sensing data in terrestrial mapping), acoustic backscatter, seafloor video, seafloor photography, 

high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products 

display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both 

the surficial seafloor geology and shallow subsurface geology. It is emphasized that the more 

interpretive habitat and geology maps rely on the integration of multiple, new high-resolution datasets 

and that mapping at small scales would not be possible without such data. 

This approach and CSMP planning is based in part on recommendations of the Marine Mapping 

Planning Workshop (Kvitek and others, 2006), attended by coastal and marine managers and scientists 

from around the state. That workshop established geographic priorities for a coastal mapping project and 

identified the need for coverage of “lands” from the shore strand line (defined as Mean Higher High 

Water; MHHW) out to the 3-nautical-mile (5.6-km) limit of California’s State Waters. Unfortunately, 

surveying the zone from MHHW out to 10-m water depth is not consistently possible using ship-based 

surveying methods, owing to sea state (for example, waves, wind, or currents), kelp coverage, and 

shallow rock outcrops. Accordingly, some of the maps presented in this series commonly do not cover 

the zone from the shore out to 10-m depth; these “no data” zones appear pale gray on most maps. 

This map is part of a series of online U.S. Geological Survey (USGS) publications, each of 

which includes several map sheets, some explanatory text, and a descriptive pamphlet. Each map sheet 

 1 U.S. Geological Survey

2 Moss Landing Marine Laboratories, Center for Habitat Studies 3 California State University, Monterey Bay, Seafloor Mapping Lab

4 California Geological Survey

5 National Oceanic and Atmospheric Administration, National Marine Fisheries Service
2

is published as a PDF file. Geographic information system (GIS) files that contain both ESRI6 ArcGIS 

raster grids (for example, bathymetry, seafloor character) and geotiffs (for example, shaded relief) are 

also included for each publication. For those who do not own the full suite of ESRI GIS and mapping 

software, the data can be read using ESRI ArcReader, a free viewer that is available at 

http://www.esri.com/software/arcgis/arcreader/index.html (last accessed March 5, 2014).

The California Seafloor Mapping Program (CSMP) is a collaborative venture between numerous 

different federal and state agencies, academia, and the private sector. CSMP partners include the 

California Coastal Conservancy, the California Ocean Protection Council, the California Department of 

Fish and Wildlife, the California Geological Survey, California State University at Monterey Bay’s 

Seafloor Mapping Lab, Moss Landing Marine Laboratories Center for Habitat Studies, Fugro Pelagos, 

Pacific Gas and Electric Company, National Oceanic and Atmospheric Administration (NOAA, 

including National Ocean Service – Office of Coast Surveys, National Marine Sanctuaries, and National 

Marine Fisheries Service), U.S. Army Corps of Engineers, the Bureau of Ocean Energy Management, 

the National Park Service, and the U.S. Geological Survey.

 6 Environmental Systems Research Institute, Inc.
3

Chapter 1. Introduction

By Guy R. Cochrane

Regional Setting

The map area offshore of Pigeon Point, California, which is referred to herein as the “Offshore of 

Pigeon Point” map area (figs. 1–1, 1–2), is located in central California, on the Pacific Coast, 50 km

south of San Francisco and 25 km northwest of Santa Cruz. The onshore part of the Offshore of Pigeon 

Point map area is sparsely populated. The nearest significant onshore cultural center is Pescadero, an 

unincorporated community with a population of well under 1,000 that lies about 2 km north of the map 

area. A large percentage of coastal land in the map area is incorporated in parks and open-space trusts. 

The hilly coastal area is virtually undeveloped, used primarily for agricultural or as grazing land for 

sheep and cattle. Agriculture is limited to the coastal uplifted Pleistocene marine terraces and upper 

Pleistocene alluvial fan deposits (see sheet 10), which lie between the shoreline and the northwesttrending Santa Cruz Mountains (fig. 1–1), part of the California Coast Ranges.

The Offshore of Pigeon Point map area is cut by the San Gregorio Fault Zone (fig. 1–2) and is 

located a few kilometers southwest of the San Andreas Fault Zone (see fig. 1–1; see also, California 

Geological Survey, 2002). The San Andreas Fault Zone is the most important structure within the 

Pacific–North American plate boundary, the only continental margin in the world delineated largely by 

transform faults (Dickinson, 2004). Coastal uplift and folding in the Offshore of Pigeon Point map area 

has been attributed to a westward bend in the San Andreas Fault Zone and also to right-lateral 

movement along the San Gregorio Fault Zone (Anderson and Menking, 1994). The irregular coastal 

geomorphology of this area, which consists of low, rocky cliffs and sparse, small pocket beaches backed 

by low, terraced hills (Griggs and others, 2005), is partly attributable to this ongoing deformation.

The offshore part of the Offshore of Pigeon Point map area primarily consists of relatively flat 

and shallow continental shelf. The shelf dips gently (less than 1°) seaward, so that water depths at the 3-

nautical-mile (5.6-km) limit of California’s State Waters range from about 65 to about 75 m. The shelf 

break, which lies approximately 20 to 26 km from the shoreline, is incised by the heads of two 

submarine canyons, which extend well into the outer continental shelf area about 6 to 10 km southsouthwest of Point Año Nuevo (see fig. 1–1). At water depths of about 130 m, the shelf break

approximates the shoreline during the sea-level lowstand of the Last Glacial Maximum (LGM), about 

21,000 years ago (see, for example, Stanford and others, 2011).

The shelf in the Offshore of Pigeon Point map area is underlain by variable amounts (0 to 20 m) 

of upper Quaternary nearshore and shelf sediments deposited during the post-LGM sea-level rise (see 

sheet 9). The thickest deposits, which are located in the northern part of the area, are probably derived 

from Pescadero Creek, a large coastal watershed that enters the Pacific Ocean about 3 km north of the 

map area, as well as from Arroyo de los Frijoles, which is presently obstructed by the Lake Lucerne 

Dam near Bean Hollow State Beach (fig. 1–2). The shelf in the southern part of the map, which lacks 

sediment supply (likely owing to its distance from large coastal watersheds), is characterized by the 

presence of uplifted bedrock that has been linked to a local zone of transpression in the San Gregorio 

Fault Zone (Weber, 1990). This uplift, coupled with high wave energy, has resulted in little or no 

sediment cover in the south where exposures of bedrock are present at water depths of as much as 45 m.

This part of central California is exposed to large North Pacific swells from the northwest 

throughout the year. North Pacific swell heights range from 2 to 10 m, the larger swells occurring from 

October to May (Storlazzi and Wingfield, 2005). During El Niño–Southern Oscillation (ENSO) events,

winter storms track farther south than they do in normal (non-ENSO) years, thereby impacting the map 

area more frequently and with waves of larger heights (Storlazzi and Wingfield, 2005). Bedrock exposed 
4

along the coast consists of erosion-resistant sedimentary rocks, and significant erosion events primarily 

are restricted to storm-wave activity that also erodes the overlying unconsolidated marine-terrace 

sediments (Griggs and others, 2005).

Coastal sediment transport in the Offshore of Pigeon Point map area is characterized by north-tosouth littoral transport of sediment that is derived mainly from streams in the Santa Cruz Mountains and 

also from local coastal erosion (Hapke and others, 2006). Shoreline-change studies indicate long-term 

erosion; within the region between San Francisco and Davenport, the highest long- and short-term 

coastal-erosion rates (-1.8 and -2.6 m/y, respectively) occur in the map area, just north of Point Año 

Nuevo (Hapke and others, 2006) (fig. 1–1). During the last approximately 300 years, as much as 18 

million cubic yards (14 million cubic meters) of sand-sized sediment has been eroded from the area 

between Año Nuevo Island and Point Año Nuevo and transported south (Griggs and others, 2005). Once 

widened by this pulse of eroded sediment, beaches south of Point Año Nuevo are now narrowing as the 

tail end of this mass of eroded sand progresses farther south (Griggs and others, 2005).

Seafloor habitats in the Offshore of Pigeon Point map area (see sheet 7 of this report) lie within 

the Shelf (continental shelf) megahabitat of Greene and others (1999). Significant rocky outcrops, which 

support kelp-forest communities in the nearshore and rocky-reef communities in deeper water, dominate 

the inner shelf waters, except for a few sand-filled paleochannels offshore of coastal creeks. In the outer 

shelf, habitats grade seaward from sand to fine-grained sand and mud. Offshore of Pigeon Point, an 

extensive area of depressions, which are caused by current scour, extends out to 50 m water depth (see 

sheet 3). 

Benthic species observed in the Offshore of Pigeon Point map area are natives of the coldtemperate biogeographic zone that is called either the “Oregonian province” (Briggs, 1974) or the 

“northern California ecoregion” (Spalding and others, 2007). This biogeographic province is maintained 

by the long-term stability of the southward-flowing California Current, the eastern limb of the North 

Pacific subtropical gyre that flows from southern British Columbia to Baja California. At its midpoint 

off central California, the California Current transports subarctic surface (0–500 m deep) waters 

southward, about 150 to 1,300 km from shore (Lynn and Simpson, 1987; Collins and others, 2000). 

Seasonal northwesterly winds (Inman and Jenkins, 1999) that are, in part, responsible for the California 

Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception

(about 335 km south of the map area), although its associated phylogeographic group of marine fauna 

may extend beyond to the area offshore of Los Angeles in southern California (Dawson and others, 

2006). The ocean off of central California has experienced a warming over the last 50 years that is 

driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical 

environment (McGowan and others, 1998).

Biological productivity resulting from coastal upwelling supports populations of Sooty 

Shearwater (Puffinus griseus), Western Gull (Larus occidentalis), Common Murre (Uria aalge), 

Cassin’s Auklet (Ptychoramphus aleuticus), and many other less populous bird species (Ainley and 

Hyrenbach, 2010). In addition, an observable recovery of Humpback and Blue Whales (Megaptera 

novaeangliae and Balaenoptera musculus, respectively) has occurred in the area; both species are 

dependent on coastal upwelling to provide nutrients (Calambokidis and Barlow, 2004). Año Nuevo State 

Park is the site of one of the largest mainland breeding colonies in the world for the Northern Elephant 

Seal (Mirounga angustirostris). The large extent of exposed inner shelf bedrock supports large forests of

“bull kelp” (Nereocystis luetkeana) (Miller and Estes, 1989), which is well adapted for high-waveenergy environments (Koehl and Wainwright, 1977). Common fish species found in the kelp beds and 

rocky reefs include blue rockfish (Sebastes mystinus), black rockfish (Sebastes melanops), olive rockfish 

(Sebastes serranoides), kelp rockfish (Sebastes atrovirens), gopher rockfish (Sebastes carnatus), blackand-yellow rockfish (Sebastes chrysomelas), painted greenling (Oxylebius pictus), kelp greenling 

(Hexagrammos decagrammus), and lingcod (Ophiodon elongatus) (Stephens and others, 2006).
5

Publication Summary 

This publication about the Offshore of Pigeon Point map area includes ten map sheets that 

contain explanatory text, in addition to this descriptive pamphlet and a data catalog of geographic

information system (GIS) files. Sheets 1, 2, and 3 combine data from three different sonar surveys to

generate comprehensive high-resolution bathymetry and acoustic-backscatter coverage of the map area. 

These data reveal a range of physiographic features (highlighted in the perspective views on sheet 4) 

such as the flat, sediment-covered, inner continental to midcontinental shelf, as well as shallow “scour 

depressions” and local, tectonically controlled bedrock uplifts. To validate geological and biological 

interpretations of the sonar data shown in sheets 1, 2, and 3, the U.S. Geological Survey towed a camera 

sled over specific offshore locations, collecting both video and photographic imagery; these “groundtruth” surveying data are summarized on sheet 6. Sheet 5 is a “seafloor character” map, which classifies 

the seafloor on the basis of depth, slope, rugosity (ruggedness), and backscatter intensity and which is 

further informed by the ground-truth-survey imagery. Sheet 7 is a map of “potential habitats,” which are 

delineated on the basis of substrate type, geomorphology, seafloor process, or other attributes that may 

provide a habitat for a specific species or assemblage of organisms. Sheet 8 compiles representative 

seismic-reflection profiles from the map area, providing information on the subsurface stratigraphy and 

structure of the map area. Sheet 9 shows the distribution and thickness of young sediment (deposited 

over the last about 21,000 years, during the most recent sea-level rise) in both the map area and the 

larger Pigeon Point to southern Monterey Bay region, interpreted on the basis of the seismic-reflection

data. Sheet 10 is a geologic map that merges onshore geologic mapping (compiled from existing maps 

by the California Geological Survey) and new offshore geologic mapping that is based on integration of 

high-resolution bathymetry and backscatter imagery (sheets 1, 2, 3), seafloor-sediment and rock samples 

(Reid and others, 2006), digital camera and video imagery (sheet 6), and high-resolution seismicreflection profiles (sheet 8). 

The information provided by the map sheets, pamphlet, and data catalog has a broad range of 

applications. High-resolution bathymetry, acoustic backscatter, ground-truth-surveying imagery, and 

habitat mapping all contribute to habitat characterization and ecosystem-based management by 

providing essential data for delineation of marine protected areas and ecosystem restoration. Many of 

the maps provide high-resolution baselines that will be critical for monitoring environmental change 

associated with climate change, coastal development, or other forcings. High-resolution bathymetry is a 

critical component for modeling coastal flooding caused by storms and tsunamis, as well as inundation 

associated with longer term sea-level rise. Seismic-reflection and bathymetric data help characterize 

earthquake and tsunami sources, critical for natural-hazard assessments of coastal zones. Information on 

sediment distribution and thickness is essential to the understanding of local and regional sediment 

transport, as well as the development of regional sediment-management plans. In addition, siting of any 

new offshore infrastructure (for example, pipelines, cables, or renewable-energy facilities) will depend 

on high-resolution mapping. Finally, this mapping will both stimulate and enable new scientific research 

and also raise public awareness of, and education about, coastal environments and issues. 
6

Figure 1–1. Physiography of Pigeon Point to southern Monterey Bay region and its environs. Box shows Offshore 

of Pigeon Point map area. Yellow line shows limit of California’s State Waters. Dashed white lines show traces

of San Gregorio Fault Zone (SGFZ) and San Andreas Fault Zone (SAFZ). Other abbreviations: MC, Monterey 

Canyon; MP, Monterey peninsula; PAN, Point Año Nuevo; PP, Pigeon Point; SCM, Santa Cruz Mountains.
7

Figure 1–2. Coastal geography of Offshore of Pigeon Point map area. Yellow line shows limit of California’s State 

Waters. Dashed white lines show trace of San Gregorio Fault Zone (SGFZ), including two major strands 

(Frijoles Fault [FF] and Coastways Fault [CF]). Other abbreviations: AF, Arroyo de los Frijoles; ANSP, Año 

Nuevo State Park.
8

Chapter 2. Bathymetry and Backscatter-Intensity Maps of the Offshore 

of Pigeon Point Map Area (Sheets 1, 2, and 3)

By Peter Dartnell and Rikk G. Kvitek

The colored shaded-relief bathymetry (sheet 1), the shaded-relief bathymetry (sheet 2), and the 

acoustic-backscatter (sheet 3) maps of the Offshore of Pigeon Point map area in central California were 

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

University, Monterey Bay (CSUMB), and by the U.S. Geological Survey (USGS) (fig. 1 on sheets 1, 2, 

3). Mapping was completed between 2006 and 2009, using a combination of 400-kHz Reson 7125 and 

244-kHz Reson 8101 multibeam echosounders, as well as a 234-kHz SWATHplus bathymetric

sidescan-sonar system. These mapping missions combined to collect both bathymetry (sheets 1, 2) and 

acoustic-backscatter data (sheet 3) 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 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, Fugro Pelagos used StarFix HP and XP real-time kinematic (RTK) GPS receivers, and 

CSUMB used a NavCom 2050 receiver; 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 water-column sound velocity using the AM SVPlus 

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

backscatter data were postprocessed using Geocoder, within which the backscatter intensities were 

radiometrically corrected (including despeckling and angle-varying gain adjustments), and the position 

of each acoustic sample was geometrically corrected for slant range on a line-by-line basis. After the 

lines were corrected, they were mosaicked into 1- or 2-m-resolution images. Overlap between parallel 

lines was resolved using a priority table whose values were based on the distance of each sample from 

the ship track, with the samples that were closest to and furthest from the ship track being given the 

lowest priority. An anti-aliasing algorithm was also applied. The mosaics were then exported as 

georeferenced TIFF images, imported into a geographic information system (GIS), and converted to 

GRIDs at 2-m resolution.

During the USGS mapping mission, GPS data with real-time-kinematic corrections were 

combined with measurements of vessel motion (heave, pitch, and roll) in a CodaOctopus F180 attitudeand-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 raytracing algorithm that works with previously measured sound-velocity profiles. Statistical filters were 

applied to discriminate seafloor returns (soundings) from unintended targets in the water column

(Ritchie and others, 2010). The backscatter data were postprocessed using USGS software (D.P. 

Finlayson, written commun., 2011) that normalizes for time-varying signal loss and beam-directivity 

differences. Thus, the raw 16-bit backscatter data were gain-normalized to enhance the backscatter of 

the SWATHplus system. The resulting normalized-amplitude values were rescaled to 16-bit and gridded 

into GeoJPEGs using GRID Processor Software, then imported into a GIS and converted to GRIDs.

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

processing software as XYZ files and bathymetric surfaces. All of the surfaces were then merged into 

one overall 2-m-resolution bathymetric-surface model and clipped to the boundary of the map area. 
9

Difference calculations of the overlapping bathymetry grids showed that there is good agreement (a 

mean difference of only 0.18 m, with 0.34 m standard deviation) between the 2006–2007 Fugro Pelagos 

and CSUMB bathymetry data and the overlapping 2009 USGS data, even though the data were collected 

at different times using different mapping systems. 

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 (sheets 1, 2). In addition, a modified 

“rainbow” color ramp was applied to the bathymetry data for sheet 1, using reds to represent shallower 

depths, and yellows to represent greater depths (note that the Offshore of Pigeon Point 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 a colored shaded-relief 

map (sheet 1). 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 (sheets 1, 2, 3, 5, 7, 10) were generated at 10-m intervals from the merged

2-m-resolution bathymetric surface. The merged surface was smoothed using the Focal Mean tool in 

ArcGIS and a circular neighborhood that has a radius of between 20 and 30 m (depending on the 

location). The contours were generated from this smoothed surface using the Spatial Analyst Contour 

tool in ArcGIS. The most continuous contour segments were preserved; smaller segments and isolated 

island polygons were excluded from the final output. The contours were then clipped to the boundary of 

the map area.

The acoustic-backscatter imagery from each mapping system and processing method were 

merged into their own individual grids. These individual grids, which cover different areas, were 

displayed in a GIS to create a composite acoustic-backscatter map (sheet 3). On the map, brighter tones 

indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity 

represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics 

within the shallow subsurface, providing a general indication of seafloor texture and composition. 

Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the 

grazing angle; the composition and character of the seafloor, including grain size, water content, bulk 

density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as 

rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), 

whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker 

tones). The differences in backscatter intensity that are apparent in some areas of the map on sheet 3 are 

due to the different frequencies of the mapping systems, as well as to different processing techniques. 

Parallel lines of higher backscatter intensity throughout the map area are data-collection and -processing 

artifacts.

The onshore-area image was generated by applying an illumination having an azimuth of 300° 

and from 45° above the horizon to 2-m-resolution topographic-lidar data from the California Coastal 

Conservancy (available from National Oceanic and Atmospheric Administration [NOAA] Coastal 

Service Center’s Digital Coast at http://www.csc.noaa.gov/digitalcoast/data/coastallidar/) and to 10-mresolution topographic-lidar data from the U.S. Geological Survey’s National Elevation Dataset 

(available at http://ned.usgs.gov/).
10

Chapter 3. Data Integration and Visualization for the Offshore of Pigeon 

Point Map Area (Sheet 4) 

By Peter Dartnell

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. For 

example, seafloor-character (sheet 5), habitat (sheet 7), and geologic (sheet 10) maps of the Offshore of 

Pigeon Point map area may assist in the designation of Marine Protected Areas, as well as in their 

monitoring. These maps and reports also help to analyze environmental change owing to sea-level rise 

and coastal development, to model and predict sediment and contaminant budgets and transport, to site 

offshore infrastructure, and to assess tsunami and earthquake hazards. To facilitate this increased 

understanding and to assist in product development, it is helpful to integrate the different datasets and 

then view the results in three-dimensional representations such as those displayed on the data integration 

and visualization sheet for the Offshore of Pigeon Point map area (sheet 4). 

The maps and three-dimensional views on sheet 4 were created using a series of geographic

information systems (GIS) and visualization techniques. Using GIS, the bathymetric and topographic 

data (sheet 1) were converted to ASCIIRASTER format files, and the acoustic-backscatter data (sheet 3) 

were converted to geotiff images. The bathymetric and topographic data were imported in the 

Fledermaus® software (QPS). The bathymetry was color-coded to closely match the colored shadedrelief bathymetry on sheet 1, in which reds represent shallower depths and yellows represent deeper 

depths; topographic data were shown in gray shades. Acoustic-backscatter geotiff images also were 

draped over the bathymetry data. The colored bathymetry, topography, and draped backscatter were then 

tilted and panned to create the perspective views such as those shown in figures 1, 2, 4, 5, and 6 on sheet 

4. These views highlight the seafloor morphology in the Offshore of Pigeon Point map area, which 

includes exposed outcrops of layered and fractured bedrock and complex patterns of shallow 

depressions.

Video-mosaic images created from digital seafloor video (for example, fig. 3 on sheet 4) display 

the geologic complexity (rock, sand, and mud; see sheet 10) and biologic complexity of the seafloor. 

Whereas photographs capture high-quality snapshots of smaller areas of the seafloor (see sheet 6), video

mosaics capture larger areas and can show transition zones between seafloor environments. Digital 

seafloor video is collected from a camera sled towed approximately 1 to 2 meters above the seafloor, at 

speeds less than 1 nautical mile/hour. Using standard video-editing software, as well as software 

developed at the Center for Coastal and Ocean Mapping, University of New Hampshire, the digital 

video is converted to AVI format, cut into 1- to 2-minute sections, and desampled to every second or 

third frame. The frames are merged together using pattern-recognition algorithms from one frame to the 

next and converted to a TIFF image. The images are then rectified to the bathymetry data using ship 

navigation recorded with the video and layback estimates of the towed camera sled.

Block diagrams that combine the bathymetry with seismic-reflection-profile data help integrate 

surface and subsurface observations, especially stratigraphic and structural relations (for example, fig. 5

on sheet 4). These block diagrams were created by converting digital seismic-reflection-profile data (see 

sheet 8) into TIFF images, while taking note of the starting and ending coordinates and maximum and 

minimum depths. The images were then imported into the Fledermaus® software as vertical images and 

merged with the bathymetry imagery.
11

Chapter 4. Seafloor-Character Map of the Offshore of Pigeon Point Map 

Area (Sheet 5)

By Mercedes D. Erdey and Guy R. Cochrane

The California State Marine Life Protection Act (MLPA) calls for protecting representative types 

of habitat in different depth zones and environmental conditions. A science team, assembled under the 

auspices of the California Department of Fish and Wildlife (CDFW), has identified seven substratedefined seafloor habitats in California’s State Waters that can be classified using sonar data and seafloor 

video and photography. These habitats include rocky banks, intertidal zones, sandy or soft ocean 

bottoms, underwater pinnacles, kelp forests, submarine canyons, and seagrass beds. The following five 

depth zones, which determine changes in species composition, have been identified: Depth Zone 1, 

intertidal; Depth Zone 2, intertidal to 30 m; Depth Zone 3, 30 to 100 m; Depth Zone 4, 100 to 200 m; 

and Depth Zone 5, deeper than 200 m (California Department of Fish and Wildlife, 2008). The CDFW 

habitats, with the exception of depth zones, can be considered a subset of a broader classification 

scheme of Greene and others (1999) that has been used by the U.S. Geological Survey (USGS) 

(Cochrane and others, 2003, 2005). These seafloor-character maps are generalized polygon shapefiles 

that have attributes derived from Greene and others (2007).

A 2007 Coastal Map Development Workshop, hosted by the USGS in Menlo Park, California, 

identified the need for more detailed (relative to Greene and others’ [1999] attributes) raster products 

that preserve some of the transitional character of the seafloor when substrates are mixed and (or) they 

change gradationally. The seafloor-character map, which delineates a subset of the CDFW habitats, is a 

GIS-derived raster product that can be produced in a consistent manner from data of variable quality 

covering large geographic regions.

The following four substrate classes are identified in the Offshore of Pigeon Point map area:

• Class I: Fine- to medium-grained smooth sediment 

• Class II: Mixed smooth sediment and rock

• Class III: Rock and boulder, rugose 

• Class IV: Medium- to coarse-grained sediment (in scour depressions)

The seafloor-character map of the Offshore of Pigeon Point map area (sheet 5) was produced

using video-supervised maximum-likelihood classification of the bathymetry and intensity of return 

from sonar systems, following the method described by Cochrane (2008). The two variants used in this 

classification were backscatter intensity and derivative rugosity. The rugosity calculation was performed 

using the Terrain Ruggedness (VRM) tool within the Benthic Terrain Modeler toolset v. 3.0 (Wright and 

others, 2012; available at http://esriurl.com/5754). 

Classes I, II, and III values were delineated using multivariate analysis. Class IV (medium- to 

coarse-grained sediment, in scour depressions) values were determined on the basis of their visual 

characteristics using both shaded-relief bathymetry and backscatter (slight depression in the seafloor, 

very high backscatter return). The resulting map (gridded at 2 m) was cleaned by hand to remove datacollection artifacts (for example, the trackline nadir). 

On the seafloor-character map (sheet 5), the four substrate classes have been colored to indicate 

the California MLPA depth zones and the Coastal and Marine Ecological Classification Standard 

(CMECS) slope zones (Madden and others, 2008) in which they belong. The California MLPA depth 

zones are Depth Zone 1 (intertidal), Depth Zone 2 (intertidal to 30 m), Depth Zone 3 (30 to 100 m), 

Depth Zone 4 (100 to 200 m), and Depth Zone 5 (greater than 200 m); in the Offshore of Pigeon Point 

map area, only Depth Zones 2 and 3 are present. The slope classes that represent the CMECS slope 
12

zones are Slope Class 1 = flat (0° to 5°), Slope Class 2 = sloping (5° to 30°), Slope Class 3 = steeply 

sloping (30° to 60°), Slope Class 4 = vertical (60° to 90°), and Slope Class 5 = overhang (greater than 

90°); in the Offshore of Pigeon Point map area, only Slope Classes 1 and 2 are present. The final

classified seafloor-character raster map image has been draped over the shaded-relief bathymetry for the 

area (sheets 1 and 2) to produce the image shown on the seafloor-character map on sheet 5.

The seafloor-character classification also is summarized on sheet 5 in table 1. Fine- to mediumgrained smooth sediment (sand and mud) makes up 79.1 percent (104.8 km2

) of the map area: 15.4 

percent (20.4 km2) is in Depth Zone 2, and 63.7 percent (84.4 km2) is in Depth Zone 3. Mixed smooth 

sediment (sand and gravel) and rock (that is, sediment typically forming a veneer over bedrock, or rock 

outcrops having little to no relief) make up 5.7 percent (7.5 km2) of the map area: 3.5 percent (4.6 km2) 

is in Depth Zone 2, and 2.2 percent (2.9 km2) is in Depth Zone 3. Rock and boulder, rugose (rock and 

boulder outcrops having high surficial complexity) makes up 13.7 percent (18.1 km2) of the map area: 

10.2 percent (13.5 km2

) is in Depth Zone 2, and 3.5 percent (4.6 km2) is in Depth Zone 3. Medium- to 

coarse-grained sediment (in scour depressions consisting of material that is coarser than the surrounding 

seafloor) makes up 1.5 percent (2.0 km2

) of the map area: 0.3 percent (0.4 km2) is in Depth Zone 2 and 

1.2 percent (1.6 km2

) is in Depth Zone 3.

A small number of video observations were used to supervise the numerical classification of the 

seafloor. All video observations (see sheet 6) are used for accuracy assessment of the seafloor-character 

map after classification. To compare observations to classified pixels, each observation point is assigned 

a class (I, II, or III), according to the visually derived, major or minor geologic component (for example,

sand or rock) and the abiotic complexity (vertical variability) of the substrate recorded during groundtruth surveys (table 4–1; see, also, chapter 5 of this pamphlet). Class IV values were assigned on the 

basis of the observation of one or more of a group of features that includes both larger scale bedforms 

(for example, sand waves), as well as sediment-filled scour depressions that resemble the “rippled scour 

depressions” of Cacchione and others (1984) and Phillips and others (2007) and also the “sorted

bedforms” of Murray and Thieler (2004), Goff and others (2005), and Trembanis and Hume (2011). On 

the geologic map (see sheet 10 of this report), they are referred to as “marine shelf scour depressions.”

Next, circular buffer areas were created around individual observation points using a 10-m radius 

to account for layback and positional inaccuracies inherent to the towed-camera system. The radius 

length is an average of the distances between the positions of sharp interfaces seen on both the video 

(the position of the ship at the time of observation) and sonar data, plus the distance covered during a 

10-second observation period at an average speed of 1 nautical mile/hour. Each buffer, which covers 

more than 300 m2, contains approximately 77 pixels. The classified (I, II, III) buffer is used as a mask to 

extract pixels from the seafloor-character map. These pixels are then compared to the class of the buffer. 

For example, if the shipboard-video observation is Class II (mixed smooth sediment and rock), but 12 of 

the 77 pixels within the buffer area are characterized as Class I (fine- to medium-grained smooth 

sediment), and 15 (of the 77) are characterized as Class III (rock and boulder, rugose), then the 

comparison would be “Class I, 12; Class II, 50; Class III, 15” (fig. 4–1). If the video observation of 

substrate is Class II, then the classification is accurate because the majority of seafloor pixels in the 

buffer are Class II. The accuracy values in table 4–2 represent the final of several classification 

iterations aimed at achieving the best accuracy, given the variable quality of sonar data (see discussion 

in Cochrane, 2008) and the limited ground-truth information available when compared to the continuous 

coverage provided by swath sonar. Presence/absence values in table 4–2 reflect the percentages of 

observations where the sediment classification of at least one pixel within the buffer zone agreed with 

the observed sediment type at a certain location.

The seafloor in the Offshore of Pigeon Point map area is covered predominantly by Class I 

sediment composed of soft, unconsolidated sand and mud. Several small exposures of rugose bedrock 

(Class III) are present in the nearshore area, and a larger area of bedrock outcrop is mapped offshore of 
13

Año Nuevo State Park. The bedrock outcrops are covered with varying thicknesses of fine (Class I) to 

coarse (Class II) sediment. Several areas of medium- to coarse-grained scour depressions (Class IV) also 

have been identified adjacent to rock outcrops.

The classification accuracy of Classes I, III, and IV (72 percent, 84 percent, and 98 percent 

accurate, respectively; table 4–2) is determined by comparing the shipboard video observations and the 

classified map. The weaker (31 percent accurate) agreement in Class II (mixed smooth sediment and 

rock and flat rock outcrop) likely is due to the relatively narrow and intermittent nature of transition 

zones from sediment to rock and also the size of the buffer. The bedrock outcrops in this area are 

composed of differentially eroded sedimentary rocks (Cochrane and Lafferty, 2002). Erosion of softer 

layers produces Class I and II sediments, resulting in patchy areas of rugose rock and boulder habitat 

(Class III) on the seafloor. A single buffered observation locale of 78 pixels, therefore, is likely to be 

interspersed with other classes of pixels, in addition to Class III. Percentages for presence/absence 

within a buffer also were calculated as a better measure of the accuracy of the classification for patchy 

rock habitat. The presence/absence accuracy was found to be significant for all classes (89 percent for 

Class I, 74 percent for Class II, 99 percent for Class III, and 100 percent for Class IV). 

Figure 4–1. Detailed view of ground-truth data, showing accuracy-assessment methodology. A, Dots illustrate 

ground-truth observation points, each of which represents 10-second window of substrate observation plotted 

over seafloor-character grid; circle around dot illustrates area of buffer depicted in B. B, Pixels of seafloorcharacter data within 10-m-radius buffer centered on one individual ground-truth video observation. 
14

Table 4–1. Conversion table showing how video observations of primary substrate (more than 50 percent seafloor 

coverage), secondary substrate (more than 20 percent seafloor coverage), and abiotic seafloor complexity (in 

first three columns) are grouped into seafloor-character-map Classes I, II, and III for use in supervised 

classification and accuracy assessment in Offshore of Pigeon Point map area.

[In areas of low visibility where primary and secondary substrate could not be identified with confidence, recorded observations of 

substrate (in fourth column) were used to assess accuracy]

Primary-substrate component Secondary-substrate component Abiotic seafloor complexity Low-visibility 

observations

Class I

mud sand trace

mud sand low

sand mud low

sand mud trace

sand sand low

sand sand trace

sediment

ripples

Class II

cobbles sand low 

cobbles sand moderate

rock sand low

rock rock low

sand boulders moderate

sand cobbles low

sand rock low

sand rock moderate

Class III

boulders boulders moderate

boulders cobbles moderate

boulders rock high

boulders rock moderate

cobbles boulders moderate

rock boulders high

rock boulders moderate

rock rock high

rock rock moderate

rock sand high

rock sand moderate
15

Table 4–2. Accuracy-assessment statistics for seafloor-character-map classifications in Offshore of Pigeon Point 

map area.

[Accuracy assessments are based on video observations]

Class Number of observations % majority % presence/absence

I—Fine- to medium-grained smooth sediment 132 72.2 89.4

II—Mixed smooth sediment and rock 39 31.0 74.4

III—Rock and boulder, rugose 166 83.6 98.8

IV—Medium- to coarse-grained sediment (in scour depressions) 42 97.6 100.0
16

Chapter 5. Ground-Truth Studies for the Offshore of Pigeon Point Map 

Area (Sheet 6)

By Nadine E. Golden and Guy R. Cochrane

To validate the interpretations of sonar data in order to turn it into geologically and biologically 

useful information, the U.S. Geological Survey (USGS) towed a camera sled (fig. 5–1) over specific 

locations throughout the Offshore of Pigeon Point map area to collect video and photographic data that 

would “ground truth” the seafloor. This ground-truth surveying occurred on two separate cruises in 2007 

and 2012. The camera sled was towed 1 to 2 m above the seafloor, at speeds of between 1 and 2 nautical 

miles/hour. Ground-truth surveys in this map area include approximately 8 trackline kilometers of video 

and 1,410 still photographs, in addition to 390 recorded seafloor observations of abiotic and biotic 

attributes. A visual estimate of slope also was recorded.

Figure 5–1. Photograph of camera sled used in USGS 2007 ground-truth survey.

During the ground-truth-survey cruises, the USGS camera sled housed two standard-definition 

(640×480 pixel resolution) video cameras (one forward looking, and one downward looking), as well as 

a high-definition (1,080×1,920 pixel resolution) video camera and an 8-megapixel digital still camera. 

During these cruises, in addition to recording the seafloor characteristics, a digital still photograph was 

captured once every 30 seconds.

The camera-sled tracklines (shown by colored dots on the map on sheet 6) are sited in order to

visually inspect areas representative of the full range of bottom hardness and rugosity in the map area. 

The video is fed in real time to the research vessel, where USGS and National Oceanic and Atmospheric 

Administration (NOAA) scientists record both the geologic and biologic character of the seafloor. While 

the camera is deployed, several different observations are recorded for a 10-second period once every 

minute, using the protocol of Anderson and others (2007). Observations of primary substrate, secondary 

substrate, slope, abiotic complexity, biotic complexity, and biotic cover are mandatory. Observations of 

key geologic features and the presence of key species also are made. 

Primary and secondary substrate, by definition, constitute greater than 50 and 20 percent of the 

seafloor, respectively, during an observation. The grain-size values that differentiate the substrate 

classes are based on the Wentworth (1922) scale, and the sand, cobble, and boulder sizes are classified 
17

as in Wentworth (1922). However, the difficulty in distinguishing the finest divisions in the Wentworth 

(1922) scale during video observations made it necessary to aggregate some grain-size classes, as was 

done in the Anderson and others (2007) methodology: the granule and pebble sizes have been grouped 

together into a class called “gravel,” and the clay and silt sizes have been grouped together into a class 

called “mud.” In addition, hard bottom and clasts larger than boulder size are classified as “rock.” 

Benthic-habitat complexity, which is divided into abiotic (geologic) and biotic (biologic) components, 

refers to the visual classification of local geologic features and biota that potentially can provide refuge 

for both juvenile and adult forms of various species (Tissot and others, 2006). 

Sheet 6 contains a smaller, simplified (depth-zone symbology has been removed) version of the 

seafloor-character map on sheet 5. On this simplified map, the camera-sled tracklines used to groundtruth-survey the sonar data are shown by aligned colored dots, each dot representing the location of a 

recorded observation. A combination of abiotic attributes (primary- and secondary-substrate 

compositions), as well as vertical variability, were used to derive the different classes represented on the 

seafloor-character map (sheet 5); on the simplified map, the derived classes are represented by colored 

dots. Also on this map are locations of the detailed views of seafloor character, shown by boxes (Boxes 

A through E); for each view, the box shows the locations (indicated by colored stars) of representative 

seafloor photographs. For each photograph, an explanation of the observed seafloor characteristics 

recorded by USGS and NOAA scientists is given. Note that individual photographs often show more 

substrate types than are reported as the primary and secondary substrate. Organisms, when present, are 

labeled on the photographs. 

The ground-truth survey is designed to investigate areas that represent the full spectrum of highresolution multibeam bathymetry and backscatter-intensity variation. Figure 5–2 shows that the seafloor 

surface in the Offshore of Pigeon Point map area predominantly consists of high-relief rocky habitat in 

the nearshore and also out to water depths of 45 m; sand habitat dominates in deeper waters (see also,

sheets 5, 7, 9).
18

Figure 5–2. Graph showing distribution of primary and secondary substrate determined from video observations in 

Offshore of Pigeon Point map area.
19

Chapter 6. Potential Marine Benthic Habitats of the Offshore of Pigeon 

Point Map Area (Sheet 7)

By H. Gary Greene and Charles A. Endris

The map on sheet 7 shows “potential” marine benthic habitats in the Offshore of Pigeon Point 

map area, representing a substrate type, geomorphology, seafloor process, or any other attribute that may 

provide a habitat for a specific species or assemblage of organisms. This map, which is based largely on 

seafloor geology, also integrates information displayed on several other thematic maps of the Offshore 

of Pigeon Point map area. High-resolution sonar bathymetry data, converted to depth grids (seafloor

DEMs; sheet 1), are essential to development of the potential marine benthic habitat map, as is shadedrelief imagery (sheet 2), which allows visualization of seafloor terrain and provides a foundation for 

interpretation of submarine landforms. 

Backscatter maps (sheet 3) also are essential for developing potential benthic habitat maps. High 

backscatter is further indication of “hard” bottom, consistent with interpretation as rock or coarse 

sediment. Low backscatter, indicative of a “soft” bottom, generally indicates a fine-sediment 

environment. Habitat interpretations also are informed by actual seafloor observations from ground-truth

surveying (sheet 6), by seafloor-character maps that are based on video-supervised maximum-likelihood 

classification (sheet 5), and by seafloor-geology maps (sheet 10). The habitat interpretations on sheet 7 

are further informed by the usSEABED bottom sampling compilation of Reid and others (2006).

Broad, generally smooth areas of seafloor that lack sharp and angular edge characteristics are 

mapped as “sediment;” these areas may be further defined by various sedimentary features (for example, 

erosional scours and depressions) and (or) depositional features (for example, dunes, mounds, or sand 

waves). In contrast, many 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. In many locations, areas within or 

around a rocky feature appear to be covered by a thin veneer of sediment; these areas are identified on 

the habitat map as “mixed” induration (that is, containing both rock and sediment). The combination of 

remotely observed data (for example, high-resolution 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 in situ

observations, video, and (or) photographic documentation.

Classifying Potential Marine Benthic Habitats

Potential marine benthic habitats in the Offshore of Pigeon Point map area are mapped using the

Benthic Marine Potential Habitat Classification Scheme, a mapping-attribute code developed by Greene 

and others (1999, 2007). This code, which has been used previously in other offshore California areas 

(see, for example, Greene and others, 2005, 2007), was developed to easily create categories of marine 

benthic habitats that can then be queried within a GIS or a database. The code contains several 

categories that can be subdivided relative to the spatial scale of the data. The following categories can be 

applied directly to habitat interpretations determined from remote-sensing imagery collected at a scale of 

tens of kilometers to one meter: Megahabitat, Seafloor Induration, Meso/Macrohabitat, Modifier, 
20

Seafloor Slope, Seafloor Complexity, and Geologic Unit. Additional categories of Macro/Microhabitat, 

Seafloor Slope, Seafloor Complexity, and Geologic Attribute can be applied to habitat interpretations 

determined from seafloor samples, video, still photographs, or direct observations at a scale of 10 meters

to a few centimeters. These two scale-dependent groups of categories can be used together, to define a 

habitat across spatial scales, or separately, to compare large- and small-scale habitat types. 

The four categories and their attribute codes that are used on the Offshore of Pigeon Point map

area are explained in detail below (note, however, that not all categories may be used in a particular map 

area, given the study objectives, data availability, or data quality); attribute codes in each category are 

depicted on the map by the letters and, in some cases, numbers that make up the map-unit symbols:

Megahabitat—Based on depth and general physiographic boundaries; used to distinguish 

features on a scale of tens of kilometers to kilometers. Depicted on map by capital letter, listed first in 

map-unit symbol; generalized depth ranges are given below: 

E = Estuary (0 to 100 m)

S = Shelf; continental and island shelves (0 to 200 m)

Seafloor Induration—Refers to substrate hardness. Depicted on map by lower-case letter, listed 

second in map-unit symbol; may be further subdivided into distinct sediment types, depicted by lowercase letter(s) in parentheses, listed immediately after substrate hardness; multiple attributes listed in 

general order of relative abundance, separated by slash; queried where inferred:

h = Hard bottom (for example, rock outcrop or sediment pavement) 

m = Mixed hard and soft bottom (for example, local sediment cover of bedrock)

s = Soft bottom; sediment cover

(b) = Boulders

(g) = Gravel

(s) = Sand

(m) = Mud, silt, and (or) clay

Meso/Macrohabitat—Related to scale of habitat; consists of seafloor features one kilometer to 

one meter in size. Depicted on map by lower-case letter and, in some cases, additional lower-case letter 

in parentheses, listed third in map-unit symbol; multiple attributes separated by slash:

(b)/p = Pinnacle indistinguishable from boulder

d = Deformed, tilted and (or) folded bedrock; overhang

e = Exposure; bedrock 

g = Gully; channel

h = Hole; depression

m = Mound; linear ridge 

p = Pinnacle; cone 

s = Scarp, cliff, fault, or slump scar

w = Dynamic bedform

Modifier—Describes texture, bedforms, biology, or lithology of seafloor. Depicted on map by 

lower-case letter, in some cases followed by additional lower-case letter(s) either after a hyphen or in 

parentheses (or both), following an underscore; multiple attributes separated by slash:

_a = Anthropogenic (artificial reef, breakwall, shipwreck, disturbance)

_a-dd = Dredge disturbance

_a-dg = Dredge groove or channel

_a-dm = Dredge mound (disposal)

_a-dp = Dredge pothole

_a-f = Ferry (or other vessel) propeller-wash scour or scar

_a-g = Groin, jetty, rip-rap

_a-p = Pipeline
21

_a-td = Trawl disturbance

_b = Bimodal (conglomeratic, mixed [gravel, cobbles, and pebbles])

_c = Consolidated sediment (claystone, mudstone, siltstone, sandstone, breccia, or 

conglomerate)

_d = Differentially eroded

_f = Fracture, joint; faulted

_g = Granite

_h = Hummocky, irregular relief

_r = Ripple (amplitude, greater than 10 cm)

_s = Scour (current or ice; direction noted)

_u = Unconsolidated sediment

Examples of Attribute Coding

To illustrate how these attribute codes can be used to describe remotely sensed data, the 

following examples are given:

Ss(s)_u = Soft, unconsolidated sediment (sand), on continental shelf.

Es(s/m)_r/u = Rippled, soft, unconsolidated sediment (sand and mud), in estuary.

She_g = Hard rock outcrop (granite), on continental shelf.

Map Area Habitats

The Offshore of Pigeon Point map area includes the nearshore and inner shelf areas from just 

north of Pigeon Point to Point Año Nuevo. Delineated on the map are 9 potential marine benthic habitat 

types, all of which are located on the continental shelf (“Shelf” megahabitat). These include soft,

unconsolidated sediment (5 habitat types) such as fine sand and mud and also just sand, as well as

dynamic features such as mobile sand sheets, sediment waves, and rippled sediment depressions; mixed 

substrate (1 habitat type) such as soft sand and gravels that overlie hard consolidated sedimentary 

bedrock and gravel pavement; and hard substrate (3 habitat types) such as deformed and differentially 

eroded bedrock, as well as pinnacles and boulders. 

Acoustic-backscatter data show that most of the area is underlain by “soft” materials, consistent 

with the interpretation that unconsolidated sediments dominate the seafloor in the map area. 

Sedimentary processes are quite active, and, thus, habitats are highly dynamic, with sediment transport 

primarily to the southeast. An extensive exposure of deformed and differentially eroded bedrock is 

located in the southeast part of the map area, offshore of Point Año Nuevo, and it potentially provides 

good habitat for rockfish (Sebastes spp.).

Of the 134.34 km2 mapped on the continental shelf in the Offshore of Pigeon Point map area, 

soft, unconsolidated sediment is the dominant habitat type, covering 108.36 km2 (80.7 percent). Hard 

rock covers 22.78 km2 (17.0 percent), and 3.19 km2 (2.4 percent) is mixed hard-soft substrate.
22

Chapter 7. Subsurface Geology and Structure of the Offshore of Pigeon 

Point Map Area and the Pigeon Point to Southern Monterey Bay Region

(Sheets 8 and 9)

By Janet T. Watt, Samuel Y. Johnson, and Stephen R. Hartwell 

The seismic-reflection profiles presented on sheet 8 provide a third dimension—depth beneath 

the seafloor—to complement the surficial seafloor-mapping data already presented (sheets 1 through 7) 

for the Offshore of Pigeon Point map area. These data, which are collected at several resolutions, extend 

to varying depths in the subsurface, depending on the purpose and mode of data acquisition. The 

seismic-reflection profiles (sheet 8) provide information on sediment character, distribution, and 

thickness, as well as potential geologic hazards, including active faults, areas prone to strong ground 

motion, and tsunamigenic slope failures. The information on faults provides essential input to national 

and state earthquake-hazard maps and assessments (see, for example, Petersen and others, 2014). 

The maps on sheet 9 show the following interpretations, which are based on the seismicreflection profiles on sheet 8: the thickness of the composite uppermost Pleistocene and Holocene 

sediment unit; the depth to base of this uppermost unit; and both the local and regional distribution of 

faults and earthquake epicenters (data from U.S. Geological Survey and California Geological Survey, 

2010; Northern California Earthquake Data Center, 2014).

Data Acquisition

Most profiles displayed on sheet 8 (figs. 1, 2, 3, 5, 6, 8, 9) were collected in 2009 and 2010 on 

U.S. Geological Survey (USGS) cruises S–N1–09–MB and S–15–10–NC, respectively. The singlechannel seismic-reflection data were acquired using a SIG 2Mille minisparker that used a 500-J highvoltage electrical discharge fired 2 times per second, which, at normal survey speeds of 4 to 4.5 nautical 

miles/hour, gives a data trace every 1.0 to 1.5 m of lateral distance covered. The data were digitally

recorded in standard SEG-Y 32-bit floating-point format, using Triton Subbottom Logger (SBL) 

software that merges seismic-reflection data with differential GPS-navigation data. After the survey, a 

short-window (20 ms) automatic gain control algorithm was applied to the data, along with a 160- to 

1,200-Hz bandpass filter and a heave correction that uses an automatic seafloor-detection window 

(averaged over 30 m of lateral distance covered). These data can resolve geologic features a few meters 

thick (and, hence, are considered “high-resolution”), down to subbottom depths of as much as 400 m. 

Figures 4 and 7 on sheet 8 show migrated, deep-penetration, multichannel seismic-reflection 

profiles collected in 1976 by WesternGeco on cruise W–14–76–SF. These profiles and other similar data 

were collected in many areas offshore of California in the 1970s and 1980s when these areas were

considered a frontier for oil and gas exploration. Much of these data have been publicly released and are

now archived at the U.S. Geological Survey National Archive of Marine Seismic Surveys (U.S. 

Geological Survey, 2009). These data were acquired using a large-volume air-gun source that has a 

frequency range of 3 to 40 Hz and recorded with a multichannel hydrophone streamer about 2 km long.

Shot spacing was about 30 m. These data can resolve geologic features that are 20 to 30 m thick, down 

to subbottom depths of as much as 4 km.

Seismic-Reflection Imaging of the Continental Shelf 

Sheet 8 shows seismic-reflection profiles in the Offshore of Pigeon Point map area, providing an 

image of the subsurface geology. The offshore part of the map area is characterized by relatively flat 

(less than 1°) inner shelf and midshelf areas, reaching water depths of about 70 m at the limit of 
23

California’s State Waters. Most of the shelf north of Point Año Nuevo is underlain by unconsolidated 

sandy and muddy sediment. Bedrock forms moderate-relief outcrops that locally extend from the 

shoreline to water depths of about 30 m, except offshore of Point Año Nuevo, where seafloor bedrock is 

exposed out to water depths of greater than 40 m (see sheets 1, 2, 10). The seismic-reflection profiles 

provide the data for interpreting subbottom stratigraphy, sediment thickness, and geologic structure (see 

sheets 9, 10). 

On seismic-reflection profiles, the Upper Cretaceous Pigeon Point Formation is essentially 

nonreflective (see figs. 1, 2, 5 on sheet 8). The overlying Tertiary strata, which are moderately to highly 

deformed, are generally characterized by continuous, parallel to subparallel, variable-amplitude, highfrequency reflections (terminology from Mitchum and others, 1977). West of the San Gregorio Fault 

Zone, the onshore Tertiary section (Brabb and others, 1998; Clark and others, 1999) includes rocks of 

the Oligocene and Miocene unnamed sedimentary and volcanic rocks unit, the middle and upper

Miocene Monterey Formation, and the upper Miocene and Pliocene Purisima Formation (Powell and 

others, 2007). Notably, the upper Miocene Santa Cruz Mudstone is absent in the onshore section west of 

the San Gregorio Fault Zone; however, the Santa Cruz Mudstone is present in offshore wells within the 

Outer Santa Cruz Basin (Heck and others, 1990), and it may also be present in the subsurface to the 

south, within the offshore part of the Offshore of Pigeon Point map area. 

Throughout the map area, the contact between the Tertiary bedrock and the overlying upper

Quaternary sediments is an angular unconformity that commonly is marked by minor channeling, an 

eastward onlap onto reflection-free bedrock, and an upward change to lower amplitude, more diffuse 

reflections. Two upper Quaternary units are recognized in the broader mapping region (see sheet 9, 

Maps C, D). Although it is not present in this map area, the lower unit notably includes low-amplitude, 

low-angle (1° to 3°), offshore-dipping clinoforms (Catuneanu, 2006). The upper unit, which is present in 

the map area, typically is characterized by low-amplitude, continuous to moderately continuous, diffuse, 

subparallel reflections, and it has a maximum thickness of about 22 m (see figs. 1, 2, 3, 5, 6, 8, 9 on 

sheet 8). 

Eustasy was an important control on late Quaternary deposition. Surficial and shallow sediments 

were deposited in the last about 21,000 years during the major sea-level lowstand associated with the 

Last Glacial Maximum (LGM) and its subsequent sea-level rise (Lambeck and Chappell, 2001; Peltier 

and Fairbanks, 2006). Global sea level was about 125 m lower than present during the LGM, at which 

time the Offshore of Pigeon Point map area was emergent and the shoreline was about 12 km west of its 

present location. Sea-level fall prior to the LGM led to the westward migration of the shoreline and 

wave-cut platform, as well as the subaerial exposure and subsequent incision of the continental shelf. 

The post-LGM sea-level rise was rapid (about 9 to 11 m per thousand years) until about 7,000 years ago,

when it slowed considerably to about 1 m per thousand years (Peltier and Fairbanks, 2006; Stanford and 

others, 2011). Post-LGM sea-level rise led to a broadening of the continental shelf, the progressive 

eastward migration of the shoreline and wave-cut platform, and the associated transgressive erosion and 

deposition.

Our preferred hypothesis is that the lower of the two upper Quaternary sedimentary units (not 

present in this map area) represents a progradational delta and (or) shoreface that formed between about 

30,000 and 21,000 years ago during the pre-LGM sea-level drop of marine-isotope stage 2 (Waelbroeck 

and others, 2002). The overlying upper unit (blue shading in profiles on sheet 8) represents shelf 

deposits that formed during the post-LGM sea-level rise of the last about 21,000 years (Stanford and 

others, 2011). In this interpretation, the surface at the base of the upper unit throughout the map area is a 

transgressive surface of erosion that formed as the shoreface migrated landward. Because the two upper

Quaternary units each consist of unconsolidated upper Quaternary sediments and together overlie the 

prominent angular unconformity with bedrock, we have combined their thicknesses on the regional

thickness maps (Maps B, D) on sheet 9
24

Geologic Structure and Recent Deformation

Faults in the offshore part of the Offshore of Pigeon Point map area are identified in seismicreflection profiles on the basis of the abrupt truncation or warping of reflections and (or) the 

juxtaposition of reflection panels that have differing seismic parameters, such as reflection presence, 

amplitude, frequency, geometry, continuity, and vertical sequence. The Offshore of Pigeon Point map 

area encompasses a part of the continental shelf that lies between the Ascension Fault and the San 

Gregorio Fault Zone, along the northeastern margin of the Outer Santa Cruz Basin and the southwest 

limb of the Pigeon Point high (McCulloch, 1987) (figs. 7, 10 on sheet 8). The Ascension Fault is a highangle reverse fault that bounds an area of uplift within the Outer Santa Cruz Basin (Nagel and others, 

1986; Wagner and others, 2002; Dickinson and others, 2005). This uplifted area on the continental shelf 

area is characterized by a number of steeply dipping, predominantly northwest-striking, unnamed faults 

that are truncated by the San Gregorio Fault Zone. These unnamed faults show a vertical separation of 

reflections and commonly juxtapose reflection panels that have differing seismic parameters, suggesting 

a combination of reverse and strike-slip faulting. This faulting is associated with a complex pattern of 

folding, particularly within the Monterey Formation offshore of Point Año Nuevo (see figs. 6, 8 on sheet 

8; see also, sheet 10). Rates of Pleistocene-age vertical uplift onshore, west of the San Gregorio Fault 

Zone, range from 0.31 to 0.35 m/ka (Clark and others, 1999), and cumulative lateral slip on the San 

Gregorio Fault Zone is thought to range from 4 to 10 mm/yr in this area (Weber and others, 1995).

Map E on sheet 9 shows the regional pattern of major faults and recorded earthquakes. Fault 

locations, which have been simplified, are compiled from our mapping within California’s State Waters 

(see sheet 10), from Wagner and others (2002), and from the U.S. Geological Survey’s Quaternary fault 

and fold database (U.S. Geological Survey and California Geological Survey, 2010). Earthquake 

epicenters are from the Northern California Earthquake Data Center (2014), which is maintained by the 

U.S. Geological Survey and the University of California, Berkeley, Seismological Laboratory; all events 

that have inferred or measured magnitudes of 2.0 and greater for the time period 1967 through April

2014 are shown. The 1989 Loma Prieta earthquake (M6.9, 10/17/1989), on the San Andreas Fault Zone 

in the Santa Cruz Mountains (Spudich, 1996), is the most significant event in the region. In the Offshore 

of Pigeon Point map area, a substantial amount of seismicity is broadly distributed between the San 

Gregorio Fault Zone and the Ascension Fault—the largest recorded earthquake (M3.6) having occurred

on 6/28/1991.

Thickness and Depth to Base of Uppermost Pleistocene and Holocene Deposits

Maps on sheet 9 show the interpreted thickness and the depth to base of uppermost Pleistocene 

and Holocene deposits, both for the Offshore of Pigeon Point map area (Maps A, B) and, to establish

regional context, for a larger area that extends about 91 km along the coast from the Pigeon Point area to 

southern Monterey Bay (Maps C, D). To make these maps, water bottom and depth to base of the 

uppermost Pleistocene and Holocene sediment layer were mapped from seismic-reflection profiles (see 

fig. 1 on sheet 9; see also, sheet 8). The difference between the two horizons was exported for every shot 

point as XY coordinates (UTM zone 10) and two-way travel time (TWT). The thickness of the 

uppermost Pleistocene and Holocene unit (Maps B, D) was determined by applying a sound velocity of 

1,600 m/sec to the TWT. The thickness points were interpolated to a preliminary continuous surface, 

overlaid with zero-thickness bedrock outcrops (see sheet 10), and contoured, following the methodology 

of Wong and others (2012). 

Several factors required manual editing of the preliminary sediment-thickness maps to make the 

final product. The Monterey Bay, San Andreas, and San Gregorio Fault Zones disrupt the sediment 

sequence in the region (Maps D, E on sheet 9). The thickness data points also are dense along tracklines 

(about 1 m apart) and sparse between tracklines (1,000 to 1,250 m apart), resulting in minor contouring 
25

artifacts. To incorporate the effects of the faults, to remove irregularities from interpolation, and to 

reflect other geologic information and complexity, the resulting interpolated contours were modified. 

Contour modifications and regridding were repeated several times to produce the final sedimentthickness maps (Maps B, D). Information for the depth to base of the uppermost Pleistocene and 

Holocene unit (Maps A, C) was generated by adding the thickness data to water depths determined by 

multibeam bathymetry (see sheet 1). 

The thickness of the post-LGM unit in the Offshore of Pigeon Point map area ranges from 0 to 

22 m (Map B on sheet 9), and the depth to the base of this unit ranges from less than 10 to 75 m (Map 

A). Mean sediment thickness for the map area is 6.0 m, and the total sediment volume is 765×106 m3

(table 7–1). The thickest sediment in the map area is found in the northwest corner of the map area (Map 

B; see also, fig. 1 on sheet 9), coincident with a decrease in slope on the bedrock unconformity (Maps A, 

C). Sediment thickness diminishes to the southeast, and the sediment cover offshore of Point Año Nuevo 

is either thin or nonexistent (Maps B, D). The extensive bedrock outcrop in this area coincides with an 

area of transpression between the Ascension Fault and the San Gregorio Fault Zone. The relative lack of 

offshore sediment probably is a result of both low sediment supply and its ongoing exposure to erosive 

wave energy.

Six different informal “domains” of thickness of uppermost Pleistocene to Holocene sediment 

(table 7–1) are recognized on the regional sediment-thickness map (Map D on sheet 9), each with its 

own diverse set of geologic and (or) oceanographic controls. Note that data from within the Monterey 

Canyon system (including Soquel Canyon), in the southern part of the Pigeon Point to southern 

Monterey Bay region, were excluded from this analysis because available seismic-reflection data are 

insufficient to map sediment distribution in this extremely variable environment. 

(1) The southern Monterey Bay domain is bounded by the Monterey Bay shoreline on the south 

and east, the Monterey Canyon on the north, and the limit of California’s State Waters on the west. 

Sediment derived from the Salinas River forms a large, shore-parallel, subaqueous delta (thickness of as 

much as 32 m) that progrades across a thinly sediment-mantled bedrock shelf. Small changes in 

sediment thickness on the shelf are controlled by irregular bedrock relief that is at least partly 

attributable to the Monterey Bay Fault Zone (Greene, 1990).

(2) The northern Monterey Bay domain is bounded on the south by Monterey Canyon, on the 

north and east by the Monterey Bay shoreline, and on the west by the limit of California’s State Waters. 

The head of Monterey Canyon extends nearly to the shoreline, and the canyon forms a sediment trap that 

effectively separates the littoral- and shelf-sediment transport systems of the two (northern and southern) 

Monterey Bay domains. The northern Monterey Bay domain is characterized by (a) a sediment-poor 

inner shelf cut by paleochannels of the San Lorenzo River, the Pajaro River, and Soquel Creek; (b) a 

midshelf depocenter that has sediment as thick as 32 m, much of which was deposited in a pre-LGM 

prograding delta and (or) shoreface complex and was preserved above a decrease in slope on the 

underlying unconformity; and (c) a midshelf to outer shelf zone in which sediment generally becomes 

progressively thinner in the offshore direction. 

(3) The Davenport shelf domain extends from the northern limit of Monterey Bay northward to 

the southern margin of the Waddell Creek depocenter. The Davenport shelf domain, as well as the three 

domains farther north, occupy a section of open, wave-dominated coast that is exposed to wave energy 

higher than that of the Monterey Bay domains to the south. The Davenport shelf domain includes the 

Davenport depocenter, a prominent midshelf, shore-parallel depocenter present between Davenport and 

Santa Cruz that mostly consists of a lower, pre-LGM, clinoform-bearing unit of inferred progradingshoreface origin. Sediment in this depocenter also is preserved in accommodation space linked to an 

offshore decrease in the slope of the underlying unconformity. Sediment thickness within the Davenport 

shelf domain decreases to both the northwest and southeast of this depocenter, owing to the presence of 

elevated bedrock and (or) the related absence of the lower clinoform-bearing unit.
26

(4) The Waddell Creek delta domain lies offshore of the mouth of the Waddell Creek coastal 

watershed, and it is connected to it by a submerged channel. The domain is both distinguished and 

delineated by the significant Waddell Creek depocenter (maximum sediment thickness of 19 m), which 

forms a moundlike delta that consists entirely of inferred post-LGM deposits whose primary source is

Waddell Creek. Sediment thins both north and south of this moundlike delta; its preservation is 

attributable to its semiprotected (from erosive wave energy) location on the south flank of Point Año 

Nuevo.

(5) The Año Nuevo shelf domain lies offshore of Point Año Nuevo, from just north of Franklin 

Point on the north to just north of the mouth of Waddell Creek on the south. Bedrock exposures, which 

locally reach water depths of 45 m, cover a substantial part of this wave-exposed domain; in deeper 

waters farther offshore, sediment cover is relatively thin. Sediment thickness in this domain appears to 

be limited both by the lack of sediment supply (because of its distance from large coastal watersheds) 

and by the presence of uplifted bedrock, which is linked to a local zone of transpression in the San 

Gregorio Fault Zone (Weber, 1990). The uplift has raised this domain and exposed it to the high wave 

energy that is characteristic of this area (Storlazzi and Wingfield, 2005).

(6) The Pigeon Point shelf domain lies on the west flank of the Pigeon Point high (McCulloch, 

1987). Sediment in the Pigeon Point shelf domain is thickest in a shore-parallel band that overlies a 

slope break in the underlying bedrock surface. Much of the sediment probably was derived from 

Pescadero Creek, a large coastal watershed that enters the Pacific Ocean about 3 km north of the Pigeon 

Point to southern Monterey Bay regional map area (see Maps C, D on sheet 9). The Pigeon Point shelf 

domain is transitional to the Pacifica-Pescadero shelf domain just north of it (see Watt and others, 2014).

Eittreim and others (2002, their fig. 15) showed an uppermost Pleistocene and Holocene 

sediment-thickness map that covers part of the area shown in Maps C and D on sheet 9 (from Point Año 

Nuevo in the north to Marina in the south). Their map combines three older investigations that cover the 

Davenport shelf (Mullins and others, 1985), Monterey Bay (Greene, 1977), and south-central Monterey 

Bay (Chin and others, 1988). These three investigations relied on analog seismic-reflection data 

collected in the 1970s and early 1980s, and they predate the availability of both digital high-resolution 

seismic-reflection data (see sheet 8) and high-resolution bathymetry (see, for example, sheets 1, 2), both

of which provided essential input to the development of the maps shown on sheet 9. Although the 

sediment-depth and -thickness patterns are grossly similar between the two generations of maps, the 

accuracy and level of detail in the newer maps is significantly higher.
27

Table 7–1. Area, sediment-thickness, and sediment-volume data for California’s State Waters in Pigeon Point to 

southern Monterey Bay region (domains 1-6), as well as in Offshore of Pigeon Point map area.

Regional sediment-thickness domains in Pigeon Point to southern Monterey Bay region

Area (km2) Mean sediment 

thickness (m)

Sediment volume 

(106 m3)

Entire Pigeon Point to southern Monterey Bay region 849 6.7 5,708

(1) Southern Monterey Bay 253 6.2 1,555

(2) Northern Monterey Bay 307 6.7 2,065

(3) Davenport shelf 134 8.3 1,113

(4) Waddell Creek delta 29 7.8 224

(5) Año Nuevo shelf 58 2.6 154

(6) Pigeon Point shelf 68 8.8 598

Sediment thickness in Offshore of Pigeon Point map area 

Entire Offshore of Pigeon Point map area 130 5.9 765

Waddell Creek delta 7 4.7 34

Año Nuevo shelf 54 2.5 134

Pigeon Point shelf 68 8.8 598
28

Chapter 8. Geologic and Geomorphic Map of the Offshore of Pigeon 

Point Map Area (Sheet 10) 

By Janet T. Watt, Stephen R. Hartwell, and Clifton W. Davenport

Geologic and Geomorphic Summary

Marine geology and geomorphology were mapped in the Offshore of Pigeon Point map area 

from approximate Mean High Water (MHW) to the 3-nautical-mile limit of California’s State Waters. 

MHW is defined at an elevation of 1.46 m above the North American Vertical Datum of 1988 (NAVD 

88) (Weber and others, 2005). Offshore geologic units were delineated on the basis of integrated 

analyses of adjacent onshore geology with multibeam bathymetry and backscatter imagery (sheets 1, 2, 

3), seafloor-sediment and rock samples (Reid and others, 2006), digital camera and video imagery (sheet 

6), and high-resolution seismic-reflection profiles (sheet 8). Aerial photographs taken in multiple years 

were used to map the nearshore area (0 to 10 m water depth) and to link the offshore and onshore 

geology. The relative proportions of all offshore map units are shown in table 8–1.

Onshore geology was compiled from Weber and Lajoie (1980), Smith (1981), California 

Geological Survey (1982a,b), Brabb (1997), Brabb and others (1998), Clark and others (1999), and 

Graymer and others (2006); unit ages, which are from these sources, reflect local stratigraphic relations. 

In addition, some units were modified by C.W. Davenport on the basis of analysis of 2012 lidar 

imagery.

The offshore part of the map area, which includes the seafloor off the prominent headland of 

Point Año Nuevo, extends from the shoreline to water depths of about 70 m. The map area is 

characterized largely by a relatively flat (less than 1°) bedrock platform that is overlain by a variably 

thick (as much as 22 m) veneer of upper Quaternary sediment (see Map B on sheet 9). Sea level has 

risen about 120 to 130 m during the last about 21,000 years (see, for example, Stanford and others, 

2011), leading to a broadening of the continental shelf, the progressive eastward migration of the 

shoreline and wave-cut platform, and the associated transgressive erosion and deposition of sediment 

(see, for example, Catuneanu, 2006). Land-derived sediment was carried into this setting and then 

subjected to Pacific Ocean wave energy and strong currents before deposition or offshore transport. 

Shelf morphology and geology are result from local faulting, folding, uplift, and subsidence.

Most of the Offshore of Pigeon Point map area encompasses a part of the continental shelf that 

lies between the Ascension Fault and the San Gregorio Fault Zone, along the northeastern margin of the 

Outer Santa Cruz Basin and the southwest limb of the Pigeon Point high (McCulloch, 1987) (fig. 1 on 

sheet 10). The northwest-striking San Gregorio Fault Zone (Weber and others, 1995; Dickinson and 

others, 2005), an important right-lateral strike-slip fault within the San Andreas Fault System, cuts 

across land through the northeast corner of the map area before moving offshore at Point Año Nuevo. In 

the map area, the San Gregorio Fault system forms a distributed shear zone about 1 to 4 km wide that 

includes two main diverging fault strands (fig. 1 on sheet 10). The west strand (known as the Frijoles 

Fault), which comes onshore approximately 0.5 km east of Año Nuevo Creek, coincides with a 

topographic trough to the north (Clark and others, 1999). The east strand (known as the Coastways 

Fault) forms a prominent scarp offshore, where rocks of the Santa Cruz Mudstone east of the fault are

juxtaposed with those of the Purisima Formation west of the fault. Paleoseismic data presented by 

Simpson and others (1997) suggest a post–late Pleistocene slip rate of 3.5 to 4.5 mm/yr for the onshore 

part of the east strand. This estimated rate represents a minimum for the San Gregorio Fault system 

because fault strands to the west, including the Frijoles Fault, are also active. Cumulative lateral slip on 

this fault zone is thought to range from 4 to 10 mm/yr in this area (Weber and others, 1995).
29

The northwest-striking Ascension Fault (fig. 1 on sheet 10) is a high-angle reverse fault (Nagel 

and others, 1986; Wagner and others, 2002; Dickinson and others, 2005) that is considered to be active 

(U.S. Geological Survey and California Geological Survey, 2010) and is characterized by a series of 

northeast-dipping thrust faults sub-parallel to the San Gregorio Fault Zone. The offshore area between 

the Ascension Fault and the San Gregorio Fault Zone is characterized by a number of steeply dipping, 

predominantly northwest-striking, unnamed faults and also northwest-trending folds.

The Upper Cretaceous Pigeon Point Formation (unit Kpp), which represents the oldest bedrock 

unit exposed in the offshore part of the map area, crops out on the seafloor in shallow water (less than 30 

meters deep) north of Point Año Nuevo and west of the San Gregorio Fault Zone. These basement rocks 

are unconformably overlain by Tertiary marine sedimentary rocks, which include the middle and upper 

Miocene Monterey Formation (unit Tm), the upper Miocene Santa Cruz Mudstone (unit Tsc), and the 

upper Miocene and Pliocene Purisima Formation (unit Tp; age from Powell and others, 2007). The 

undivided Oligocene to upper Pliocene sedimentary rocks unit (Tu) is mapped in the offshore where 

assignment to a particular formation is uncertain; this undivided unit may also include a relatively thin 

(85 m thick) section of volcanic rocks, which has been mapped onshore along the coast at Point Año 

Nuevo as the unnamed sedimentary and volcanic rocks unit (Tuv).

The Santa Cruz Mudstone (Tsc) is mapped east of the Coastways Fault (east strand of the San 

Gregorio Fault Zone) both in the nearshore and onshore in the seacliff. However, the Santa Cruz 

Mudstone is not present within the Tertiary section onshore west of the Coastways Fault, where the 

Purisima Formation unconformably overlies either the Pigeon Point Formation or the Monterey 

Formation. The Purisima Formation is exposed on the seafloor in Año Nuevo Bay between the 

Coastways and Frijoles Faults. Seafloor exposures of the Purisima Formation and the underlying 

Monterey Formation are difficult to distinguish west of the Frijoles Fault in multibeam bathymetry 

imagery (see sheets 1, 2); however, the faulted unconformity between the Purisima and Monterey 

Formations is clearly visible in seismic-reflection profiles southeast of Point Año Nuevo (see fig. 9 on 

sheet 8).

Modern nearshore sediments are mostly sand (unit Qms) and a mix of sand, gravel, and cobbles

(units Qmsc and Qmsd). Unit Qms notably is present, in addition to on the shelf, in well-defined 

channels that cut through nearshore bedrock exposures north of Pigeon Point. These distinct channels, 

which extend to water depths of 20 to 30 m, were formed by subaerial erosion during sea-level 

lowstands (Anima and others, 2002). The coarser grained sands and gravels (units Qmsc and Qmsd) 

are recognized primarily on the basis of bathymetry and high backscatter (see sheets 1, 2, 3). Unit Qmsc

mainly is found adjacent to bedrock, in water depths of less than 40 m.

Unit Qmsd typically is mapped as erosional lags in scour depressions (see, for example, 

Cacchione and others, 1984) that are bounded by relatively sharp or, less commonly, diffuse contacts 

with the horizontal sand sheets of unit Qms. These depressions typically are a few tens of centimeters 

deep and range in size from a few tens of square meters to more than 1 km2. Such scour depressions are 

common along this stretch of the California coast (see, for example, Cacchione and others, 1984; 

Hallenbeck and others, 2012; Davis and others, 2013), where offshore sandy sediment can be relatively 

thin (and, thus, is unable to fill the depressions) owing to low sediment supply from rivers and also to 

significant erosion and offshore transport of sediment during large northwest winter swells. Such 

features have been referred to as “rippled scour depressions” (see, for example, Cacchione and others, 

1984) or “sorted bedforms” (see, for example, Murray and Thieler, 2004; Goff and others, 2005; 

Trembanis and Hume, 2011). Although the general areas in which both unit Qmsd scour depressions 

and surrounding Qms sand sheets are found are not likely to change substantially, the boundaries of the 

unit(s) likely are ephemeral, changing seasonally and during significant storm events.

A transition to finer grained marine sediments (unit Qmsf) is seen offshore of Pigeon Point and 

southwest of Point Año Nuevo, at water depths of 50 to 60 m. Unit Qmsf, which commonly is 
30

extensively bioturbated, primarily consists of mud and muddy sand. These fine-grained shelf sediments 

are derived from local coastal watersheds, bluff erosion, and the northward advection of sediment from 

fluvial sources within, and north of, Monterey Bay (Edwards, 2002).

In areas where shelf sediments form thin (less than 2.5 m) veneers over low-relief rocks of the 

upper Miocene and Pliocene Purisima Formation, composite unit Qms/Tp is mapped. This composite 

unit is recognized on the basis of the combination of flat relief, continuity with moderate- to high-relief 

bedrock outcrops, high-resolution seismic-reflection data (see sheet 8), and moderate to high backscatter

(see sheet 3). Overlying sediment is interpreted as an ephemeral and dynamic sediment layer that may or 

may not be continuously present, depending on storms, seasonal and (or) annual patterns of sediment 

movement, or longer term climate cycles. Storlazzi and others (2011) described the seasonal burial and 

exhumation of submerged bedrock in a similar high-energy setting in northern Monterey Bay, just south 

of the map area. 

Table 8–1. Areas and relative proportions of offshore geologic map units in Offshore of Pigeon Point map area.

Map Unit Area (m2) Area (km2) Percent of total area

Marine sedimentary units

Qms 79,718,281 79.7 57.7

Qmsc 1,045,303 1.0 0.8

Qmsd 2,087,107 2.1 1.5

Qmsf 23,740,499 23.7 17.2

Total, sedimentary units 106,591,191 106.5 77.2

Marine bedrock and (or) shallow bedrock units

Qms/Tp 87,656 0.1 0.1

Tm 15,103,036 15.1 10.9

Tp 4,102,837 4.1 3.0

Tsc 401,293 0.4 0.3

Tu 318,979 0.3 0.2

Kpp 11,494,770 11.5 8.3

Total, bedrock units 31,508,571 31.5 22.8

Total, Offshore of Pigeon Point map area 138,099,762 138.1 100.0
31

DESCRIPTION OF MAP UNITS

OFFSHORE GEOLOGIC AND GEOMORPHIC UNITS

[Note that, where older units (typically, bedrock) are overlain by thin (<1 m thick) Quaternary deposits, 

composite units are mapped. These composite units, which are shown with gray stipple pattern on older 

unit, are designated by composite label indicating both overlying sediment cover and lower (older) unit, 

separated by slash (for example, Qms/Tp indicates that thin sheet of Qms overlies Tp)]

Qms Marine nearshore and shelf deposits (late Holocene)—Predominantly sand and some mud; 

ripple marks common; found on seaward-dipping surface that extends from shoreline 

to west edge of map area

Qmsd Marine shelf scour depressions (late Holocene)—Inferred to be coarse sand and possibly 

gravel; consists of irregular, arcuate scour depressions that range from solitary 

features that occupy a few hundred square meters to fields of interconnected 

depressions covering tens of thousands of square meters. Found as single depressions 

or in fields of depressions interspersed with elevated shelf sediments (units Qms and 

Qmsf). Depressions are typically are 15 to 50 cm deep and have sharp to diffuse 

boundaries. General area in which unit is found is not likely to change substantially, 

but boundaries of unit(s) and locations of individual depressions (and intervening flat 

sheets) likely are ephemeral, changing during significant storm events

Qmsf Fine-grained marine shelf deposits (late Holocene)—Predominantly mud, very fine sand,

and silt; found at water depths greater than about 60 m 

Qmsc Coarse-grained marine nearshore and shelf deposits (late Holocene)—Predominantly 

coarse sand and gravel

Tp Purisima Formation (Pliocene and late Miocene)—Predominantly gray and greenish-gray

to buff, fine-grained marine sandstone, siltstone, and mudstone; also includes some 

porcelaneous shale and mudstone, chert, silty mudstone, and volcanic ash. Stippled 

areas (composite unit Qms/Tp) indicate where thin sheets of Qms overlie unit. Age 

is based on biostratigraphic and geochronologic data summarized by Powell and 

others (2007)

Tu Sedimentary and volcanic rocks, undivided (late Pliocene to Oligocene)—Consists of 

rocks of the Purisima Formation (Tp), the Monterey Formation (Tm), and the 

unnamed sedimentary and volcanic rocks unit (Tuv) 

Tsc Santa Cruz Mudstone (late Miocene)—Thin- to thick-bedded, marine, siliceous and 

nonsiliceous mudstone and siltstone; includes minor amounts of sandstone 

Tm Monterey Formation (late and middle Miocene)—Marine, thin-bedded, porcelaneous 

shale and chert, porcelaneous mudstone, diatomite, claystone; includes siltstone and 

sandstone near base. Visible in multibeam-bathymetry imagery as highly fractured 

bedrock exposed on seafloor offshore of Point Año Nuevo

Kpp Pigeon Point Formation (Late Cretaceous)—Sandstone and conglomerate, interbedded 

with siltstone and mudstone. Exposed on seafloor in nearshore (less than 30 m deep) 

offshore of Pigeon Point and Franklin Point
32

ONSHORE GEOLOGIC AND GEOMORPHIC UNITS

[Units compiled from Weber and Lajoie (1980), Smith (1981), California Geological Survey (1982a,b), 

Brabb (1997), Brabb and others (1998), Clark and others (1999), and Graymer and others (2006); unit 

ages, which are from these sources, reflect local stratigraphic relations. In addition, some units modified 

by C.W. Davenport on basis of analysis of 2012 lidar imagery]

af Artificial fill (late Holocene)—Rock, sand, and mud, deposited by humans

adf Artificial-dam fill (late Holocene)—Earth- or rock-fill dams, embankments, and levees; 

constructed to impound land-locked water bodies

Qbs Beach-sand deposits (late Holocene)—Active beaches in coastal environments; may form 

veneer over bedrock platform

Qf Alluvial fan deposits (late Holocene)—Alluvial fan deposits judged to be late Holocene 

(<1,000 years) in age, on basis of records of historical inundation or presence of 

youthful braid bars and distributary channels

Qds Dune-sand deposits (Holocene)—Active and recently stabilized dunes, in coastal

environments

Qa Alluvial deposits, undivided (Holocene)—Alluvium deposited in fan, terrace, or basin 

environments

Qyf Alluvial fan deposits (Holocene)—Sediment deposited by streams emanating from 

mountain canyons onto alluvial valley floors or alluvial plains; may include sand, 

gravel, silt, and clay; deposits identified primarily by fan morphology and 

topographic expression

Qb Basin deposits (Holocene)—Fine-grained sediment that accumulates from standing or slowmoving water in topographic basins and, locally, between adjacent alluvial fans

Qt Stream-terrace deposits (Holocene)—Relatively smooth, undissected, relatively low-lying 

terraces adjacent to active stream channels

Qcl Colluvium (Holocene)—Loose to firm, unsorted sand, silt, clay, gravel, rock debris, and 

organic material, in varying proportions

Qls Landslide deposits (Holocene and Pleistocene)—Disintegrated bedrock; physically 

weathered; ranges from deep-seated landslides to active colluvium; queried where 

uncertain

Qot Stream-terrace deposits (Holocene and late Pleistocene)—Sand, gravel, silt, and minor 

clay of uncertain age; underlies relatively flat platforms adjacent to stream channels

Qya Alluvial deposits, undivided (late Pleistocene)—Mapped on gently sloping to level terrace 

surfaces, where late Pleistocene age is indicated by depth of stream incision; also 

mapped where separate units could not be delineated at map scale

Qof2 Alluvial fan deposits (late Pleistocene)—Mapped where late Pleistocene age is indicated by 

greater degree of dissection, than is present on Holocene fans, or where geomorphic 

feature lies at higher elevation, than that of Holocene fans

Qmt Marine-terrace deposits, undivided (Pleistocene)—Sand and gravel; deposited on uplifted 

marine-abrasion platforms along coast; queried where uncertain. Locally includes 

dune sand where too small or numerous to show at map scale 

Qoa Older alluvial deposits, undivided (Pleistocene)—Moderately to deeply dissected alluvial 

deposits; commonly consists of gently rolling hills that have little or no original 

planar surface preserved

Qof1 Alluvial fan deposits (Pleistocene)—Moderately to deeply dissected alluvial fan deposits; 

mapped where some original fan surface morphology is preserved 

Tp Purisima Formation (Pliocene and late Miocene)—Medium-grained to very fine-grained, 
33

poorly indurated to friable sandstone, siltstone, and claystone; also includes

conglomerate lenses and a few beds of white volcanic ash

Tsc Santa Cruz Mudstone (late Miocene)—Siliceous mudstone, interbedded with nonsiliceous 

mudstone, siltstone, and minor sandstone

Tsm Santa Margarita Sandstone (late Miocene)—Friable, very fine- to very coarse-grained, 

arkosic sandstone; quartz- and feldspar-pebble conglomerate crops out locally at base 

of section

Tm Monterey Formation (late and middle Miocene)—Porcelaneous shale and chert, 

porcelaneous mudstone, calcareous claystone; includes small amounts of siltstone and 

sandstone near base

Tuv Unnamed sedimentary and volcanic rocks (Miocene and Oligocene)—Dark-gray, hard 

mudstone

Tb Butano Sandstone (middle and early Eocene)—Very fine- to very coarse-grained, arkosic 

sandstone, interbedded with mudstone and shale; conglomerate is present locally in 

lower part of section

Kpp Pigeon Point Formation (Late Cretaceous)—Sandstone and conglomerate, interbedded 

with siltstone and mudstone

KJv Unnamed volcanic rocks (Cretaceous or Jurassic)—Finely crystalline, felsic volcanic 

rocks that contain quartz and albite phenocrysts
34

Acknowledgments

This publication was funded by the California Ocean Protection Council and the U.S. Geological 

Survey (USGS) Coastal and Marine Geology Program. We thank the officers, crew, and scientific 

parties of the ships—R/V VenTresca, California State University, Monterey Bay, Seafloor Mapping 

Lab; F/V Quicksilver, Fugro Pelagos; and R/V Parke Snavely, USGS Pacific Coastal and Marine 

Science Center—for their skill and professionalism in collecting the data presented in this report. We 

thank Mary Young (University of California, Santa Cruz) and Robert Peters (USGS) for their critical 

reviews that greatly improved this report. We are very grateful to USGS editor Taryn Lindquist for

helping us develop the templates and formats for this series of publications, and for invaluable editorial 

review and suggestions.
35

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