California State Waters Map Series—Offshore of Scott 

Creek, California

By Guy R. Cochrane, Peter Dartnell, Samuel Y. Johnson, H. Gary Greene, Mercedes D. Erdey, Bryan E. Dieter, 

Nadine E. Golden, Charles A. Endris, Stephen R. Hartwell, Rikk G. Kvitek, Clifton W. Davenport, Janet T. Watt, 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 2015–1191

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., Dartnell, P., Johnson, S.Y., Greene, H.G., Erdey, M.D., Dieter, B.E., Golden, N.E., Endris, C.A., 

Hartwell, S.R., Kvitek, R.G., Davenport, C.W., Watt, J.T., 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 Scott Creek, California: U.S. Geological Survey Open-File Report 2015–1191, pamphlet 40 p., 10 

sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20151191.

ISSN 2331-1258 (online)
iii

Contents

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

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

By Guy R. Cochrane ................................................................................................................................ 3

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

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

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

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

By Peter Dartnell and Rikk G. Kvitek........................................................................................................ 8

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

By Peter Dartnell .................................................................................................................................... 10

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

By Mercedes D. Erdey and Guy R. Cochrane........................................................................................ 11

Chapter 5. Ground-Truth Studies for the Offshore of Scott Creek Map Area (Sheet 6)................................................15

By Nadine E. Golden and Guy R. Cochrane .......................................................................................... 15

Chapter 6. Potential Marine Benthic Habitats of the Offshore of Scott Creek Map Area (Sheet 7) ..............................18

By H. Gary Greene and Charles A. Endris ............................................................................................. 18

Classifying Potential Marine Benthic Habitats ..........................................................................................................18

Examples of Attribute Coding ...................................................................................................................................20

Map Area Habitats....................................................................................................................................................20

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

Southern Monterey Bay Region (Sheets 8 and 9)........................................................................................................21

By Samuel Y. Johnson, Stephen R. Hartwell, Janet T. Watt, and Katherine L. Maier............................ 21

Data Acquisition........................................................................................................................................................21

Seismic-Reflection Imaging of the Continental Shelf ................................................................................................21

Geologic Structure and Recent Deformation ............................................................................................................22

Thickness and Depth to Base of Uppermost Pleistocene and Holocene Deposits ...................................................23

Chapter 8. Geologic and Geomorphic Map of the Offshore of Scott Creek Map Area (Sheet 10)................................27

By Samuel Y. Johnson, Stephen R. Hartwell, and Clifton W. Davenport ............................................... 27

Geologic and Geomorphic Summary........................................................................................................................27

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

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

Onshore Geologic and Geomorphic Units ............................................................................................................31

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 Scott Creek 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..................................................... 15

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

Offshore of Scott Creek map area. ......................................................................................................... 17

Figure 8–1. Schematic map showing major offshore structural features northwest of Monterey Bay ........................ 30
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 Scott Creek map area....................... 14

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

map area .................................................................................................................................................. 14

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 Scott Creek map area............... 26

Table 8–1. Areas and relative proportions of offshore geologic map units in Offshore of Scott Creek map area ....... 28

Map Sheets

Sheet 1. Colored Shaded-Relief Bathymetry, Offshore of Scott Creek Map Area, California

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

Sheet 2. Shaded-Relief Bathymetry, Offshore of Scott Creek Map Area, California 

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

Sheet 3. Acoustic Backscatter, Offshore of Scott Creek Map Area, California 

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

Sheet 4. Data Integration and Visualization, Offshore of Scott Creek Map Area, California 

By Peter Dartnell 

Sheet 5. Seafloor Character, Offshore of Scott Creek Map Area, California 

By Mercedes D. Erdey and Guy R. Cochrane 

Sheet 6. Ground-Truth Studies, Offshore of Scott Creek Map Area, California 

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

Sheet 7. Potential Marine Benthic Habitats, Offshore of Scott Creek Map Area, California 

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

Sheet 8. Seismic-Reflection Profiles, Offshore of Scott Creek Map Area, California 

By Samuel Y. Johnson, Stephen R. Hartwell, and Ray W. Sliter

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

Monterey Bay) Shallow-Subsurface Geology and Structure, California 

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

Sheet 10. Offshore and Onshore Geology and Geomorphology, Offshore of Scott Creek Map Area, California 

By Stephen R. Hartwell, Samuel Y. Johnson, and Clifton W. Davenport
1

California State Waters Map Series—Offshore of Scott 

Creek, California

By Guy R. Cochrane,1 Peter Dartnell,

1 Samuel Y. Johnson,1 H. Gary Greene,2 Mercedes D. Erdey,1 Bryan E. 

Dieter,2 Nadine E. Golden,1 Charles A. Endris,2 Stephen R. Hartwell,1 Rikk G. Kvitek,3 Clifton W. Davenport,4 Janet 

T. Watt,1 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 the mouth of Scott Creek, in central California, which is referred to 

herein as the “Offshore of Scott Creek” map area (figs. 1–1, 1–2), is located on the Pacific Coast, 65 km

south of San Francisco and 12 km northwest of Santa Cruz. The onshore part of the Offshore of Scott 

Creek map area is sparsely populated. The only onshore cultural center is Davenport (fig. 1–2), a small 

community with a population of less than 500 that lies on the coast near the east edge of the map area. 

The hilly coastal area is virtually undeveloped, and a large percentage of coastal land in the map area is 

incorporated in open-space trusts. A lumber mill is on the south flank of Waddell Creek (fig. 1–2), and a 

large cement plant once operated in Davenport but closed in 2010. Agricultural land (much of which is 

owned by California Polytechnic State University, San Luis Obispo, and operated partly as a remote 

campus for agricultural science) is almost entirely limited to coastal areas between the shoreline and the 

northwest-trending Santa Cruz Mountains (fig. 1–1), on Pleistocene alluvial fan deposits and the lowest 

emergent marine terrace (see sheet 10). The Santa Cruz Mountains are part of the northwest-trending 

Coast Ranges that run roughly parallel to the San Andreas Fault Zone (California Geological Survey, 

2002). 

The map area is cut by an offshore section of the San Gregorio Fault Zone (fig. 1–2), and it lies 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). Regional folding and uplift along the coast 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 Scott Creek 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 50 to about 65 m. The shelf 

break, which lies approximately 12 to 20 km from the shoreline, is incised by the heads of several 

submarine canyons, two of which extend north-northeast well into the outer continental shelf area (see 

fig. 1–1; see also, lower left corner of fig. 1–2). 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 Scott Creek map area is underlain by variable amounts (0 to 25 m) 

of upper Quaternary shelf, nearshore, and fluvial sediments deposited as sea level fluctuated in the late 

Pleistocene (see sheet 9). The northernmost part of the map area is characterized by the presence of 

uplifted bedrock that has been linked to a local transpressional zone in the San Gregorio Fault Zone 

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

this area where exposures of bedrock are present at water depths of as much as 45 m. The thickest 

deposits of sediment lie offshore of both Davenport and the mouth of Waddell Creek (see sheet 9). 

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 
4

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

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 Scott Creek 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 north of the Offshore of Scott Creek 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 in the Offshore of Scott 

Creek map area are now narrowing as the tail end of this mass of sand progresses farther south (Griggs 

and others, 2005). 

Seafloor habitats in the Offshore of Scott Creek 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. Sand-filled paleochannels cut through the rocky reefs offshore of coastal creeks. 

In the midshelf to outer shelf areas, habitats grade seaward from sand to fine-grained sand and mud. 

Offshore of Davenport, 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 Scott Creek 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 320 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). 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-wave-energy environments (Koehl and Wainwright, 1977). 

The kelp beds are the northernmost known habitat for the population of southern sea otters (Enhydra 

lutris nereis) (Tinker and others, 2008). 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), black-and-yellow 
5

rockfish (Sebastes chrysomelas), painted greenling (Oxylebius pictus), kelp greenling (Hexagrammos 

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

Publication Summary 

This publication about the Offshore of Scott Creek 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 four 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 Scott Creek 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 Scott Creek map area. Yellow line shows limit of California’s State 

Waters. Dashed white line shows trace of San Gregorio Fault Zone (SGFZ). Other abbreviations: AP, Agua 

Puera Creek; SC, Scott Creek; SV, San Vincente Creek; WC, Waddell Creek. 
8

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

of Scott Creek 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 Scott Creek 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 a 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 Scott Creek 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 Scott 

Creek 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 

Scott Creek 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 Scott Creek 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 Scott Creek map area, which 

includes an extensive, featureless, sedimented seafloor, as well as layered, folded, and fractured 

bedrock. 

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. 6 

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 Scott Creek 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 Scott Creek 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 Scott Creek 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 Scott Creek 

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 Scott Creek 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 80.6 percent (103.2 km2

) of the map area: 9.1 

percent (11.7 km2) is in Depth Zone 2, and 71.5 percent (91.5 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 8.1 percent (10.3 km2) of the map area: 2.7 percent (3.5 km2) 

is in Depth Zone 2, and 5.4 percent (6.8 km2) is in Depth Zone 3. Rock and boulder, rugose (rock and 

boulder outcrops having high surficial complexity) makes up 10.4 percent (13.3 km2

) of the map area: 

7.4 percent (9.4 km2) is in Depth Zone 2, and 3.0 percent (3.9 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 0.9 percent (1.2 km2) of the map area: 0.1 percent (0.1 km2) is in Depth Zone 2, and 

0.8 percent (1.1 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 Scott Creek map area is covered predominantly by Class I 

sediment composed of soft, unconsolidated sand and mud. Several exposures of the deformed and 

differentially eroded rocks of the Santa Cruz Mudstone (Class III) are present in the nearshore area
13

offshore of Scott Creek and Davenport. The northern part of the map area is dominated by exposures of 

the Monterey and Purisima Formations offshore of Point Año Nuevo. 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, most commonly adjacent to rock 

outcrops, and they reach water depths of about 55 m. 

The classification accuracy of Classes I, III, and IV (73 percent, 67 percent, and 92 percent 

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

classified map. The weaker (33 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 (90 percent for 

Class I, 64 percent for Class II, 95 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 Scott Creek 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 low 

sand mud low 

sand mud trace 

sand sand low 

sediment 

 ripples 

Class II

cobbles sand low 

rock mud low 

rock sand low 

rock rock low 

boulders sand moderate 

sand cobbles low 

sand rock low 

sand rock moderate 

Class III

boulders cobbles moderate 

boulders rock moderate 

cobbles boulders moderate 

rock boulders high

rock boulders moderate

rock cobbles moderate 

rock rock high

rock rock moderate 

rock sand high

rock sand moderate 

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

map area. 

[Accuracy assessments are based on video observations] 

Class Number of observations % majority % presence/absence

I—Fine- to medium-grained smooth sediment 190 72.6 90.0

II—Mixed smooth sediment and rock 38 32.9 64.4

III—Rock and boulder, rugose 168 66.9 94.9

IV—Medium- to coarse-grained sediment (in scour depressions) 31 91.9 100.0
15

Chapter 5. Ground-Truth Studies for the Offshore of Scott Creek 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 Scott Creek map area to collect video and photographic data that 

would “ground truth” the seafloor. This ground-truth surveying occurred in 2007, 2010, 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 3,700 

still photographs, in addition to 548 recorded seafloor observations of abiotic and biotic attributes. A 

visual estimate of slope also was recorded.

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 

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

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

(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 Scott Creek map area predominantly consists of high-relief rocky habitat in 

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

(see also, sheets 5, 7, 9). 
17

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

Offshore of Scott Creek map area.
18

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

Creek 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 Scott Creek 

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 Scott Creek 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 Scott Creek 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, 

Seafloor Slope, Seafloor Complexity, and Geologic Unit. Additional categories of Macro/Microhabitat, 
19

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 Scott Creek 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

_a-td = Trawl disturbance 
20

_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 Scott Creek map area includes the nearshore and inner shelf areas from just 

south of Point Año Nuevo to the vicinity of Davenport. Delineated on the map are nine potential marine 

benthic habitat types, all on the continental shelf (“Shelf” megahabitat). These include soft, 

unconsolidated sediment (6 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 (2 habitat types) such as deformed and differentially 

eroded bedrock and also 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, especially on the inner shelf just south of Point Año Nuevo, 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 northern part of the map area, 

offshore of Point Año Nuevo and Año Nuevo Island, and it extends in the nearshore area all the way to 

Davenport; such areas of rocky seafloor potentially provide good habitat for rockfish (Sebastes spp.). 

Of the 128.49 km2

 mapped on the continental shelf in the Offshore of Scott Creek map area, soft, 

unconsolidated sediment is the dominant habitat type, covering 109.01 km2 (84.8 percent). Hard rock 

covers 18.58 km2

 (14.5 percent), and 0.91 km2 (0.7 percent) is mixed hard-soft substrate.
21

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

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

(Sheets 8 and 9)

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

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 Scott Creek 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, 4, 6, 7, 9, 10) were collected in 2009 on U.S. 

Geological Survey (USGS) cruise S–N1–09–MB. The single-channel seismic-reflection data were 

acquired using a SIG 2Mille minisparker that used a 500-J high-voltage 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 floatingpoint 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 “highresolution”), down to subbottom depths of as much as 400 m. 

Figures 5 and 8 on sheet 8 show migrated, deep-penetration, multichannel seismic-reflection 

profiles collected in 1976 and 1982 by WesternGeco on cruises W–14–76–SF and W–34–82–MB, 

respectively. 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 Scott Creek map area, providing an 

image of the subsurface geology. The offshore part of the map area consists of gently (about 0.6° to 

0.8°) offshore-dipping nearshore, inner shelf, and midshelf areas, reaching water depths of about 70 m at 
22

the limit of California’s State Waters. Most of the shelf is underlain by flat, sandy and muddy sediment; 

in addition, bedrock forms moderate-relief outcrops that locally extend from the shoreline out to water 

depths of as much as 45 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).

The high-resolution seismic-reflection profiles on sheet 8 (figs. 1, 2, 3, 4, 6, 7, 9, 10) show a 

lower unit of deformed Neogene bedrock and one or two upper units (pink and blue shading) that consist 

of upper Quaternary sediments. Bedrock is characterized by folded and faulted, moderate- to highamplitude, variably continuous, parallel to subparallel reflections (terminology from Mitchum and 

others, 1977). 

Throughout the map area, the contact between the Neogene 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 high-resolution profiles on sheet 8. The 

lower unit (pink shading; figs. 2, 4, 7), which is present only in the south half of the map area, is as thick 

as 15 m, and it notably includes low-amplitude, low-angle (1° to 3°), offshore-dipping clinoforms 

(Catuneanu, 2006). The upper unit (blue shading; figs. 1, 2, 3, 4, 6, 7, 9, 10) typically is characterized by 

low-amplitude, continuous to moderately continuous, diffuse, subparallel reflections, and it has a 

maximum thickness of about 12 m. 

Eustasy was an important control on late Quaternary deposition. Global sea level was about 125 

m lower than present during the Last Glacial Maximum (LGM) about 21,000 years ago, at which time 

the Offshore of Scott Creek map area was emergent and the shoreline was about 12 to 15 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 clinoforms in the lower (pink shading in profiles on sheet 8) 

of the two upper Quaternary units represent a progradational 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 thickness

maps (Maps B, D) on sheet 9.

Geologic Structure and Recent Deformation

The Offshore of Scott Creek map area straddles the right-lateral San Gregorio Fault Zone, an 

important structure in the distributed transform boundary between the North American and Pacific plates 

(see, for example, Dickinson and others, 2005). This fault zone is part of a fault system that is present 

predominantly in the offshore for about 400 km, from Point Conception in the south (where it is known 

as the Hosgri Fault; Johnson and Watt, 2012) to Bolinas and Point Reyes in the north (Bruns and others, 

2002; Ryan and others, 2008). The San Gregorio Fault Zone in the map area is part of a 90-km-long 

offshore segment that extends northward from Point Sur (about 75 km south of the map area), across 
23

outer Monterey Bay to Point Año Nuevo (1 km north of the map area) (see sheet 9; see also, Weber and 

Lajoie, 1980; Brabb and others, 1998; Wagner and others, 2002). Offshore parts of this fault zone are 

identified in seismic-reflection 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 amplitude, 

frequency, geometry, continuity, and vertical sequence. In this map area, the San Gregorio Fault forms a 

distributed shear zone about 2 km wide that includes two main fault strands (see figs. 2, 3, 4, 6, 7, 9 on 

sheet 8; see also, sheet 10). The nearshore east strand, known as the Coastways Fault, partly coincides 

with a prominent bathymetric lineament on the outer flank of nearshore bedrock outcrops present 

between Davenport and the mouth of Waddell Creek (see sheets 1, 2). The west strand, known as the 

Frijoles Fault, cuts across the flat, sediment-covered shelf. Underlying strata east of the Coastways Fault 

consist of the upper Miocene Santa Cruz Mudstone; west of the fault, underlying strata are inferred to 

consist of a mix of Neogene rocks that include the middle and upper Miocene Monterey Formation, the 

upper Miocene and Pliocene Purisima Formation, and possibly the upper Miocene Santa Cruz 

Mudstone. Cumulative lateral slip on the San Gregorio Fault Zone is thought to range from 4 to 10 

mm/yr based on offset shoreline angles and drainages at Point Año Nuevo (Weber, 1994). 

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. The largest 

recorded earthquake in the Offshore of Scott Creek map area (M3.8, 12/24/1979) occurred within the 

San Gregorio Fault Zone. 

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 Scott Creek 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 

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 
24

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 uppermost Pleistocene and Holocene sediments in the Offshore of Scott 

Creek map area ranges from 0 to 24 m (Map B on sheet 9), and the depth to the unconformity at the base 

of this unit ranges from less than 10 to 87 m (Map A). Mean sediment thickness for the map area is 7.3 

m, and the total sediment volume is 885×106 m3 (table 7–1). The thickest sediment in the map area is 

found in two discrete depocenters. The more northern of the two depocenters, the “Waddell Creek 

depocenter,” has a maximum sediment thickness of 19 m and consists entirely of younger, post-LGM 

deposits (Map B; see also, fig. 3 on sheet 8). This depocenter overlies a uniformly offshore-dipping 

basement surface (Map A), indicating that it forms a low-relief mound on the seafloor. This low-relief 

mound is continuous with a lowstand fluvial channel cut into bedrock at the mouth of Waddell Creek 

(Map B), the presumed primary sediment source for this depocenter. Preservation of this low-relief 

sediment mound is due, in part, to its more protected (from wave energy) location on the south flank of 

the protruding bedrock high associated with Point Año Nuevo and Año Nuevo Island. 

The more southern of the two depocenters, the “Davenport depocenter,” is found southwest of 

Davenport, and it has a maximum sediment thickness of 24 m (Map B). Most of this sediment is part of 

the lower clinoform-bearing unit (pink shading in profiles; see fig. 1 on sheet 9; see also, figs. 2, 4, 7 on 

sheet 8) of inferred pre-LGM, regressive origin. The upper Quaternary sediments in the depocenter form 

a lens that thins in both the onshore and offshore directions (see, for example, fig. 1 on sheet 9), and the 

axis of the depocenter coincides with an offshore decrease in slope of the underlying unconformity, from 

about 1.0° to 0.5°. The thicker sediment effectively fills the accommodation space above the slope 

change, giving the modern continental shelf a relatively smooth, offshore-dipping (about 0.6° to 0.8°) 

profile. The clinoforms are not present at the mouths of significant coastal watersheds and, thus, are 

inferred to represent an offshore-prograding shoreface, rather than prograding delta foresets. 

The decreased thickness of upper Quaternary sediments between the two shelf depocenters in the 

map area results primarily from decreased depths to the underlying bedrock unconformity (Maps A, C 

on sheet 9). Elevated bedrock between the depocenters locally crops out on the seafloor (see sheet 10) 

and coincides with a broad anticline. As with the southeastern depocenter, accommodation space is 

created by a decrease in slope on the unconformity (from 1.0° to as low as 0.2°); however, this space is 

not filled with sediment, presumably because of its shallower water depths and also its greater exposure 

to erosive wave energy during the transgression. 

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 
25

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. 

(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.
26

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 Scott Creek 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 Scott Creek map area

Entire Offshore of Scott Creek map area 122 7.3 885

Map area within Davenport shelf 69 8.6 594

Waddell Creek delta 29 7.8 224

Map area within Año Nuevo Davenport shelf 24 2.8 67
27

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

Creek Map Area (Sheet 10) 

By Samuel Y. Johnson, Stephen R. Hartwell, and Clifton W. Davenport

Geologic and Geomorphic Summary

Marine geology and geomorphology were mapped in the Offshore of Scott Creek 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), seafloorsediment 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. 

The onshore geology was compiled from Smith (1981), California Geological Survey (1982), 

Brabb (1997), 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 2009 lidar imagery. 

The offshore part of the map area lies southwest of the southwest flank of the Santa Cruz 

Mountains, extending from the shoreline to water depths of about 60 to 75 m on the gently dipping 

(about 0.6° to 0.8°) continental shelf. The shelf is underlain by Neogene bedrock and a variably thick (as 

much as 24 m) upper Quaternary sediment cover (see 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 broadening 

of the continental shelf, progressive eastward migration of the shoreline and wave-cut platform, and 

associated transgressive erosion and deposition of sediment (see, for example, Catuneanu, 2006). The 

Offshore of Scott Creek map area is now an open-ocean shelf that is subjected to full, and sometimes 

severe, wave energy. Shelf morphology and geology also are affected by local faulting, folding, uplift, 

and possibly subsidence. 

The Offshore of Scott Creek map area straddles the right-lateral San Gregorio Fault Zone, an 

important structure in the distributed transform boundary between the North American and Pacific plates 

(see, for example, Dickinson and others, 2005). This fault zone is part of a regional fault system that is 

present predominantly in the offshore for about 400 km, from Point Conception in the south (where it is 

known as the Hosgri Fault; Johnson and Watt, 2012) to Bolinas and Point Reyes in the north (Bruns and 

others, 2002; Ryan and others, 2008). The San Gregorio Fault Zone in the map area is part of a 90-kmlong offshore segment that extends northward from Point Sur (about 75 km south of the map area), 

across outer Monterey Bay to Point Año Nuevo (1 km north of the map area) (see sheet 9; see also, 

Weber and Lajoie, 1980; Brabb and others, 1998; Wagner and others, 2002). Offshore parts of this fault 

zone are identified in seismic-reflection profiles on the basis of abrupt truncation or warping of 

reflections and (or) the juxtaposition of reflection panels that have differing seismic parameters (see 

sheet 8). In this map area, the San Gregorio Fault forms a distributed shear zone about 2 km wide that 

includes two main fault strands. The nearshore east strand, known as the Coastways Fault, partly 

coincides with a prominent bathymetric lineament on the outer flank of nearshore bedrock outcrops 

present between Davenport and the mouth of Waddell Creek (see sheets 1, 2). The west strand, known 

as the Frijoles Fault, cuts across the flat, sediment-covered shelf. Cumulative lateral slip on the San 

Gregorio Fault Zone is thought to range from 4 to 10 mm/yr on the basis of field observations at Point 

Año Nuevo (Weber, 1994). 
28

Table 8–1. Areas and relative proportions of offshore geologic map units in Offshore of Scott Creek map area. 

Map Unit Area (m2) Area (km2) Percent of total area

Marine sedimentary units

Qms 56,528,963 56.5 43.9

Qmsd 1,190,534 1.2 0.9

Qmsc 857,825 0.9 0.7

Qmsf 45,209,044 45.2 35.1

Total, sedimentary units 103,786,367 103.8 80.6

Marine bedrock and (or) shallow bedrock units

Qms/Tp 87,656 0.1 0.1

Tp 1,340,740 1.3 1.0

Tsc 16,984,315 17.0 13.2

Tm 6,306,176 6.3 4.9

Tu 198,623 0.2 0.2

Total, bedrock units 24,917,510 24.9 19.4

Total, Offshore of Scott Creek map area 128,703,876 128.7 100.0

McCulloch (1987) considered the San Gregorio Fault Zone to be the eastern margin of the Outer 

Santa Cruz Basin (fig. 8–1). Farther offshore, outside California’s State Waters but within the map area, 

this basin is cut by the northwest-striking Ascension Fault (Greene and others, 2002; U.S. Geological 

Survey and California Geological Survey, 2010). 

Emergent marine terraces on the flanks of the Santa Cruz Mountains between Santa Cruz and 

Point Año Nuevo (fig. 1–1) are as high as 240 m. Estimated rates of uplift range from about 0.2 

mm/year (see, for example, Bradley and Griggs, 1976; Lajoie and others, 1991) to as much as 1.1 mm/yr 

(see, for example, Perg and others, 2001). This uplift has been attributed to a combination of two 

processes, (1) advection of crust around a bend in the San Andreas Fault Zone (fig. 1–1), and (2) uplift 

on the northeast (landward) side of the steeply northeast-dipping San Gregorio Fault Zone (Anderson, 

1990; Anderson and Menking, 1994). The area of uplift in this tectonic model includes the nearshore 

and shelf areas in the Offshore of Scott Creek map area, but considerable shore-normal uplift gradients

are associated with both processes, and offshore rates of uplift are not well constrained. 

The seafloor outcrops of the Miocene Monterey Formation (unit Tm) and the upper Miocene and 

Pliocene Purisima Formation (unit Tp; Powell and others, 2007) that are found along the north edge of 

the map area are continuous with onshore and nearshore outcrops at Point Año Nuevo to the north (fig. 

1–1). Outcrops of the Monterey Formation are characterized by differentially eroded layers (harder and 

softer interbeds) that are folded and densely fractured, creating an overall “shattered” appearance on 

shaded-relief maps (see sheets 1, 2). Adjacent seafloor outcrops of the Purisima Formation are similarly 

folded but notably are much less fractured and, thus, have a distinctly different geomorphic expression. 

Outcrops of both the Monterey Formation and the Purisima Formation are found west of the Coastways 

Fault, and outcrops of the Purisima Formation straddle the Frijoles Fault.

The upper Miocene Santa Cruz Mudstone (unit Tsc) forms onshore and nearshore outcrops on 

the east flank of the Coastways Fault, and it notably does not crop out west of the Coastways Fault. 

Seafloor outcrops reveal both folding and fracturing, although not to the extent of that of the Monterey 

Formation to the west. Four midshelf bedrock outcrops in the central part of the map area (in the outer 

reaches of California’s State Waters) are mapped as the undivided Miocene and Pliocene sedimentary

rocks unit (Tu); these outcrops may consist of rocks of the Monterey Formation (Tm), the Santa Cruz 

Mudstone (Tsc), or the Purisima Formation (Tp).
29

Modern nearshore and inner shelf to midshelf sediments are mostly sand (unit Qms) and a mix 

of sand and gravel (units Qmsc and Qmsd). Unit Qms notably is also present in well-defined channels 

that cut through nearshore bedrock exposures at the mouths of Waddell Creek, Scott Creek, Agua Puera 

Creek, and San Vicente Creek (fig. 1–2). These distinct channels, which extend to water depths of 20 to 

40 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 (or) 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 irregular to lenticular and a 

few tens of centimeters deep, and they range in size from a few tens of square meters to as much as 

about 290,000 m2. They most commonly are found adjacent to seafloor bedrock exposures, at water 

depths that range from about 15 to 55 m. 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, 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. 

An offshore transition from unit Qms to the finer grained marine sediments of unit Qmsf is 

present at water depths of 50 to 65 m. Unit Qmsf primarily consists of mud and muddy sand and 

commonly is extensively bioturbated. These fine-grained shelf sediments are derived from local coastal 

watersheds, bluff erosion, and the northward advection of sediment from fluvial sources within 

Monterey Bay (Edwards, 2002; Grossman and others, 2006). 

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, 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 highenergy setting in northern Monterey Bay, just south of the map area. 
30

Figure 8–1. Schematic map showing major offshore structural features northwest of Monterey Bay (modified from 

McCulloch, 1987; Greene and others, 2002; Dickinson, 2005). Red box shows Offshore of Scott Creek map 

area. Yellow line shows limit of California’s State Waters. Outer Santa Cruz Basin (modified from McCulloch, 

1987) shown by blue shading and hachured lines (hachures point into basin). Solid black lines show traces of 

faults: AF, Ascension Fault (sawteeth on upper plate); CF, Coastways Fault; FF, Frijoles Fault; SGFZ, San 

Gregorio Fault Zone (also shown by dark-gray shading); SAF, San Andreas Fault; ZYF, Zayante-Vergeles 

Fault. Dashed magenta lines show axes of structural highs: PPH, Pigeon Point high; SCH, Santa Cruz high. 

Other abbreviations: PAN, Point Año Nuevo; PP, Pigeon Point.
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; ripple marks 

common; found on gently seaward-dipping (about 0.6° to 0.8°) surface that extends 

from shoreline to water depths of about 50 to 65 m 

Qmsd Marine shelf scour depressions (late Holocene)—Inferred to be coarse sand and possibly 

gravel; generally found as single depressions or in groups of depressions interspersed 

with elevated shelf sediments (unit Qms), adjacent to and (or) offshore of bedrock 

outcrops. Depressions typically have curved to irregular margins and diffuse to sharp 

boundaries, and they typically are 15 to 50 cm deep. In map area, backscatter data 

show intensity contrasts that suggest depressions are filled with sediment that is 

coarser than intervening elevated sandy shelf deposits. 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 

Qmsc Coarse-grained marine nearshore and shelf deposits (late Holocene)—Predominantly 

coarse sand and gravel 

Qmsf Fine-grained marine shelf deposits (late Holocene)—Predominantly mud to muddy sand; 

commonly bioturbated; found on gently seaward-dipping (less than 1°) surfaces, in 

water depths greater than about 50 to 65 m 

Tp Purisima Formation (Pliocene and late Miocene)—Medium-grained to very fine-grained, 

poorly indurated to friable, marine sandstone, siltstone, and claystone; also includes 

conglomerate lenses and a few beds of white 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 rocks, undivided (Pliocene and Miocene)—May consist of rocks of the 

Purisima Formation (Tp), the Santa Cruz Mudstone (Tsc), or the Monterey 

Formation (Tm) 

Tsc Santa Cruz Mudstone (late Miocene)—Siliceous organic mudstone and nonsiliceous 

mudstone, siltstone, and minor amounts of sandstone 

Tm Monterey Formation (late and middle Miocene)—Porcelaneous shale and chert, 

porcelaneous mudstone, calcareous claystone, and small amounts of siltstone and 

sandstone 

ONSHORE GEOLOGIC AND GEOMORPHIC UNITS

[Units compiled from Smith (1981), California Geological Survey (1982), Brabb (1997), 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 2009 lidar imagery] 

af Artificial fill (late Holocene)—Material placed by humans 

Qc Stream-channel deposits (late Holocene)—Sand and gravel deposits within active stream 

channels 
32

Qbs Beach-sand deposits (late Holocene)—Fine to very coarse sand that forms active beaches in 

coastal environments; may make veneer over bedrock platform. Locally, can include 

dune-sand deposits too small to delineate at map scale 

Qf Alluvial fan deposits (late Holocene)—Sediments derived from hillslopes in lower valley of 

Scott Creek; may include debris-flow and braided-stream deposits; judged to be latest 

Holocene (<1,000 years old) in age, on basis of records of historical inundation, 

location with respect to older alluvial fans, or presence of youthful braid bars and 

distributary channels

Qt Stream-terrace deposits (Holocene)—Relatively smooth and undissected, low-lying 

terraces; found immediately adjacent to lower reaches of active stream channels 

Qa Alluvial deposits, undivided (Holocene)—Alluvium deposited along stream channels; 

mapped in valley bottoms along small- to medium-sized streams. Locally, may 

include small terrace and channel deposits where such features are too small to 

delineate at map scale

Qds Dune-sand deposits (Holocene)—Very well-sorted, fine to medium sand that forms both 

active and stabilized dunes in coastal environments 

Qcl Colluvium (Holocene)—Loose to firm, unsorted sand, silt, clay, gravel, rock debris, and 

organic material, in varying proportions; typically mapped in hillside swales and 

narrow immature drainages; can contain numerous small landslides and (or) alluvial 

fans

Qls Landslide deposits (Holocene and Pleistocene)—Weathered and disintegrated rocks and 

soil; ranges from deep-seated landslides to active colluvium 

Qyf Alluvial fan deposits (Holocene)—Sediment (sand, gravel, silt, clay) deposited by streams 

emanating from canyons onto alluvial plains; identified primarily by fan morphology 

and topographic expression 

Qyt Stream-terrace deposits (Holocene)—Relatively smooth, undissected, relatively low-lying 

terraces adjacent to active stream channels

Qoa Alluvial deposits, undivided (Holocene and late Pleistocene)—Found on gently sloping to 

level terrace surfaces adjacent to stream channels, where separate units could not be 

delineated at map scale

Qot Stream-terrace deposits (Holocene and late Pleistocene)—Sand, gravel, silt, and minor 

clay of uncertain age; underlies relatively flat platforms adjacent to, and elevated 

above, stream channels

Qof Alluvial fan deposits (late Pleistocene)—Sediment deposited by streams emanating from 

canyons; mapped where late Pleistocene age is indicated by greater degree of 

dissection, or where geomorphic landform lies at higher elevation, than that of 

adjacent fans of inferred Holocene age

Qmt2 Lowest emergent marine-terrace deposits (Pleistocene)—Semiconsolidated sand and less 

common gravel deposits, on uplifted marine-abrasion platforms along coast; locally 

may include fluvial and (or) sand-dune deposits that are too small or numerous to 

delineate at map scale; queried where uncertain

Qmt1 Marine-terrace deposits, undivided (Pleistocene)—Semiconsolidated sand and less 

common gravel deposits, on uplifted marine-abrasion platforms along coast; locally 

may include fluvial and (or) colluvial deposits that are too small or numerous to 

delineate at map scale; found at higher elevations than Qmt2

Tsc Santa Cruz Mudstone (late Miocene)—Pale-yellowish-brown, siliceous, organic mudstone 

and nonsiliceous mudstone, siltstone, and minor amounts of sandstone 
33

Tsm Santa Margarita Sandstone (late Miocene)—Friable, yellowish-grey to white, medium- to 

fine-grained arkosic sandstone; locally calcareous and bituminous; base of section has 

local pebble conglomerate 

Kqd Quartz diorite (Cretaceous)

 Metasedimentary rocks (Mesozoic or Paleozoic)—Mainly pelitic schist and quartzite
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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