Geology and geomorphology--Offshore of Bodega Head Map Area, California

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What does this data set describe?

Title:
Geology and geomorphology--Offshore of Bodega Head Map Area, California
Abstract:
This part of DS 781 presents data for the geologic and geomorphic map of the Offshore of Bodega Head map area, California. The vector data file is included in "Geology_OffshoreBodegaHead.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreBodegaHead/data_catalog_OffshoreBodegaHead.html.
The morphology and the geology of the Offshore of Bodega Head map area result from the interplay between tectonics, sea-level rise, local sedimentary processes, and oceanography. The Offshore of Bodega Head map area is cut by the northwest-trending San Andreas Fault, the right-lateral transform boundary between the North American and Pacific tectonic plates. From southeast to northwest, this fault extends through Bodega Bay and Bodega Harbor, crosses the Bodega Head isthmus at the mouth of Salmon Creek, and extends in the offshore for about 20 km before passing onland at Fort Ross, about 12 km north of the Offshore of Bodega Head map area. The San Andreas Fault juxtaposes Cretaceous granitic rock on the southwest with the Jurassic, Cretaceous, and early Tertiary Franciscan Complex on the northeast. Uplift of the granitic rock (unit Kg) on the west side of the San Andreas Fault has created extensive, rugged, rocky seafloor, centered offshore Bodega Head and extending northwest for about 15 km, from the western flank of Bodega Bay to the shelf offshore of the mouth of Salmon Creek. At its south and north ends this rocky seafloor extends to water depths of about 40 m and 50 m, respectively where it is onlapped by young sediment (see below); offshore of Bodega Head, the rocky seafloor extends to water depths of 80 m. Northeast of the San Andreas Fault, offshore rocky outcrops of the Franciscan complex (units Kfs, Kjfss, fsr) occur only in the nearshore (water depths less than 15 m).
Sediment-covered areas of the offshore part of the map occur in gently sloping (less than about 1 degree) nearshore, inner-, and mid-shelf environments. Sediment supply to the shelf north and west of Bodega Head is predominantly from coastal watersheds including the Russian River (4.5 km north of the map area) and Salmon Creek. Sediment supply to Bodega Bay and the shelf in the southern part of the map area is from small coastal watersheds and estuaries such as Estero Americano and Estero de San Antonio, and most likely from sediment flux out of the mouth of Tomales Bay, located two kilometers south of the map area. Shelf morphology and evolution largely reflects eustacy; sea level has risen about 125 to 130 m over about the last 21,000 years (for example, Lambeck and Chappell, 2001; Peltier and Fairbanks, 2005), leading to broadening of the continental shelf, progressive eastward migration of the shoreline and wave-cut platform, and associated transgressive erosion and deposition.
Given present exposure to high wave energy, modern nearshore to inner-shelf sediments are mostly sand (unit Qms) and a mix of sand, gravel, and cobbles (units Qmsc and Qmsd). The more coarse-grained sands and gravels (units Qmsc and Qmsd) are primarily recognized on the basis of bathymetry and high backscatter. Unit Qmsc occurs in two areas: (1) as a linear nearshore bar (water depth less than 10 m) offshore of Salmon Creek - the eastern contact of this unit is queried because of the lack of data in the surf zone; and (2) as a west-trending bar at the north end of Bodega Bay. Unit Qmsd forms erosional lags in scoured depressions that are bounded by relatively sharp contacts with bedrock or sharp to diffuse contacts with unit Qms. These scoured depressions are typically a few tens of centimeters deep and range in size from a few 10's of sq m to more than one sq km.
Similar unit Qmsd scour depressions are common along this stretch of the California coast (see, for example, Cacchione and others, 1984; Hallenbeck and others, 2012) where surficial offshore sandy sediment is relatively thin (thus unable to fill the depressions) due to both lack of sediment supply and to erosion and 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 mobile sand sheets occur are not likely to change substantially, the boundaries of the individual Qmsd depressions are likely ephemeral, changing seasonally and during significant storm events.
Unit Qmsf lies offshore of unit Qms, consists primarily of mud and muddy sand and is commonly extensively bioturbated. The water depth of the transition from sand-dominated marine sediment (unit Qms) to mud-dominated marine sediment (Qmsf) occurs at depths of about 45 to 50 m except offshore of Bodega Head where seafloor bedrock outcrops extend to depths of 80 m at the outer limit of California's State Waters.
The smooth seafloor in the northern part of the map area between water depths of 40 m and 70 m notably includes an about 3-km-wide field of elongate, shore-normal, paired sediment lobes and chutes (unit Qmsl). Individual lobes within the field are as much as 1,000-m long and 150-m wide, and have as much as 2 m of relief above the surrounding smooth seafloor. This sediment-lobe field lies just one kilometer west of the San Andreas Fault and we infer that large earthquakes on this structure generated strong ground motions and slope failures, mobilizing small sediment flows that moved down the gentle slope and were deposited as lobes. Unit Qmsl also occurs as a 250-m-wide field of four discrete lobes and paired arcuate, low-relief scours on the south flank of a west-trending bar in northern Bodega Bay.
Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data (see Bathymetry--Offshore Bodega Head, California and Backscattter A to C--Offshore Bodega Head, California, DS 781, for more information). The bathymetry and backscatter data were collected between 2007 and 2010.
References Cited
Cacchione, D.A., Drake, D.E., Grant, W.D., and Tate, G.B., 1984, Rippled scour depressions of the inner continental shelf off central California: Journal of Sedimentary Petrology, v. 54, p. 1,280-1,291.
Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms or "rippled scour depressions", within the Martha’s Vineyard Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461-484.
Hallenbeck, T.R., Kvitek, R.G., and Lindholm, J., 2012, Rippled scour depressions add ecologically significant heterogeneity to soft-bottom habitats on the continental shelf: Marine Ecology Progress Series, v. 468, p. 119-133.
Lambeck, K., and Chappell, J., 2001, Sea level change through the last glacial cycle: Science, v. 292, p. 679-686, doi: 10.1126/science.1059549.
Peltier, W.R., and Fairbanks, R.G., 2006, Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record: Quaternary Science Reviews, v. 25, p. 3,322-3,337.
Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand-Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203-214.
Supplemental_Information:
Map political location: San Mateo County, California Compilation scale: 1:24,000 Base maps used are hillshades generated from IfSAR, LiDAR, and multibeam mapping both onshore and offshore (see Bathymetry Hillshade--Offshore Bodega Head, California, California, DS 781, for more information).
  1. How might this data set be cited?
    Johnson, S.Y., Hartwell, S.R., and Manson, M.W., 2014, Geology and geomorphology--Offshore of Bodega Head Map Area, California:.

    This is part of the following larger work.

    Golden, Nadine E., 2013, California State Waters Map Series Data Catalog: Data Series DS 781, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -123.17
    East_Bounding_Coordinate: -122.97
    North_Bounding_Coordinate: 38.41
    South_Bounding_Coordinate: 38.25
  3. What does it look like?
    <http://pubs.usgs.gov/ds/781/OffshoreBodegaHead/images/Geology_OffshoreBodegaHead.jpg> (JPEG)
    Geology and geomorphology offshore Bodega Head.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2006
    Ending_Date: 2010
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • GT-polygon composed of chains (352)
    2. What coordinate system is used to represent geographic features?
      The map projection used is WGS 1984 UTM Zone 10N.
      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.0001
      Ordinates (y-coordinates) are specified to the nearest 0.0001
      Planar coordinates are specified in Meter
      The horizontal datum used is D WGS 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    MapUnits
    Polygons representing geologic / geomorphic map units (Source: This report)
    OBJECTID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    MapUnitAbbrev
    Map Unit abbreviation (Source: This report)
    ValueDefinition
    QmsMarine nearshore and shelf deposits
    QmsdMarine shelf scour depressions
    QmscCoarse-grained marine nearshore and shelf deposits
    QmsfFine-grained marine shelf deposits
    QmslSediment lobes
    KgGranitic rocks of Bodega Head
    KfsFranciscan Complex sandstone in Central Belt
    fsrFranciscan Complex mélange in Central Belt
    gsFranciscan Complex greenstone blocks within mélange
    MapUnit
    short description of map unit (Source: This report) text description of map unit
    Shape_Length
    Length of feature in internal units. (Source: ESRI) Positive real numbers that are automatically generated.
    Shape_Area
    Area of feature in internal units squared. (Source: ESRI) Positive real numbers that are automatically generated.
    RuleID
    Representation rule identifier (Source: This report) This field contains the representation rule in the ArcGIS file geodatabase which applies a solid color fill of a specified CMYK value to each polygon. Representation rules have the same name as the map unit abbreviation.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • S.Y. Johnson
    • S.R. Hartwell
    • M.W. Manson
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    USGS Pacific Coastal and Marine Science Center
    Attn: Stephen Hartwell
    Geologist
    400 Natural Bridges Drive
    Santa Cruz, CA
    USA

    (831) 460-7814 (voice)
    (831) 427-4748 (FAX)
    shartwell@usgs.gov

Why was the data set created?

To expand geologic mapping to the seafloor within the California's State Waters, to update coastal geologic mapping, and to contribute to a uniform regional geologic database, which can be used geographic information systems. Additionally, to provide a geologic map for the public and geoscience community to aid in assessments and mitigation of geologic hazards in the Bodega Bay coastal region and to provide sufficient geologic information for land-use and land-management decisions both onshore and offshore. This information is not intended for navigational purposes.

How was the data set created?

  1. From what previous works were the data drawn?
    DS 781 (source 1 of 3)
    Dartnell, Peter, and Kvitek, Rikk G., 2013, Bathymetry--Offshore of Bodega Head Map Area, California: Data Series DS 781, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    See metadata for bathymetry ("Bathymetry_OffshoreBodegaHead_metadata.txt") in DS 781 for source data and postprocessing/reprocessing information.
    Type_of_Source_Media: digital file of gridded bathymetry data (ArcInfo GRID)
    Source_Contribution: Gridded bathymetry data (2-meter resolution).
    DS 781 (source 2 of 3)
    Other_Citation_Details:
    See metadata for backsctter data ("BackscatterA_8101_OffshoreBodegaHead_metadata.txt", "BackscatterB_7125_OffshoreBodegaHead_metadata.txt", and "BackscatterC_Swath_OffshoreBodegaHead_metadata.txt") in DS 781 for amplitude source data and postprocessing/reprocessing information.
    Type_of_Source_Media: digital file of gridded amplitude data (ArcInfo GRID)
    Source_Contribution: Gridded amplitude data (2-meter resolution).
    S-15-10-NC (source 3 of 3)
    U.S. Geological Survey (USGS), Coastal and Marine Geology Program (CMGP), 2013, Seismic-reflection data acquisition data of field activity S-15-10-NC in offshore Pescadero from 08/02/2010 to 08/04/2010: U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG), Menlo Park, CA.

    Online Links:

    Type_of_Source_Media: ASCII lat/long shot point files
    Source_Contribution:
    Digital seismic data used to interpret subsurface geologic structure
  2. How were the data generated, processed, and modified?
    Date: 2013 (process 1 of 6)
    Faults were mapped onto shot lines based on the latitude and longitude of seismic picks from field activity S-15-10-NC.
    Date: 2012 (process 2 of 6)
    Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data. Derivatives such as slope and curvature were generated from source rasters. Interpreted rasters include amplitude, hillshaded bathymetry (using various illumination angles and vertical exaggeration), slope, and curvature. Curvature was decomposed into profile and plan curvature for analysis purposes.
    Date: 2013 (process 3 of 6)
    The mapped area was extended to the shoreline by using digital orthophotos to interpret the region between the inner edge of the multibeam bathymetry and the approximate shoreline. The approximate shoreline was generated at the NAVD88 +1.46 m contour, defined as the operational MHW shoreline by Weber and others (2005). The resulting boundary was transformed to WGS 84 UTM Zone 10 North in ArcGIS 10 using the NAD83 to WGS84 (ITRF00) transformation algorithm. This boundary was then used to extend and trim both onshore and offshore geology in the print and PDF product. The transformed boundary is contained within the WGS84 "contours" feature class and identified as a water boundary in the associated representation rules.
    Only data for offshore map units are released digitally in this publication. For onshore geology see Blake and others (2002) and Wagner and Gutierrez (2010; in press). Quaternary mapping units are as defined by Witter and others (2006) and Wagner and Gutierrez (2010), with unit contacts modified based on analysis of 2003 LiDAR and 2004 IfSAR and data; and additional unpublished mapping by M.W. Manson. San Andreas Fault traces are from Brown and Wolfe (1972), California Geological Survey (1974) and previously unpublished mapping by M.W. Manson.
    References Cited:
    Blake, M.C., Jr., Graymer, R.W., and Stamski, R.E., 2002, Geologic map and map database of western Sonoma, northernmost Marin, and southernmost Mendocino counties, California: U.S. Geological Survey Miscellaneous Field Studies Map 2402, scale 1:100,000.
    Brown, R.D., Jr., and Wolfe, E.W., 1972, Map showing recently active breaks along the San Andreas Fault between Point Delgada and Bolinas Bay, California: U.S. Geological Survey Miscellaneous Investigations Map I-692, scale 1:24,000.
    California Geological Survey, 1974, Alquist-Priolo Earthquake Fault Zone Maps of Bodega Head, Duncans Mills and Valley Ford quadrangles, scale 1:24,000.
    Fuller, M.S., Haydon, W.D., Purcell, M.G., and Custis, K., 2002, Geologic and geomorphic features related to landsliding, Gualala River watershed, Sonoma and Mendocino counties, California: California Geological Survey Watershed Mapping Series, Map Set 5, Plate 1, Sheet 3 of 3, scale 1:24,000.
    Manson, M.W., Huyette, C.M., Wills, C.J., Huffman, M.E., Smelser, G.G., Fuller, M.E., Domrose, C., and Gutierrez, C., 2006, Landslides in the Highway 1 corridor between Bodega Bay and Fort Ross, Sonoma County, California: California Geological Survey Special Report 196, 26 p., 2 plates, 38 maps, scale 1:12,000.
    Wagner, D.L., and Gutierrez, C.I., 2010, Preliminary Geologic Map of the Napa 30’ x 60’ Quadrangle, California: California Geological Survey, scale 1:100,000.
    Wagner, D.L., and Gutierrez, C.I., in press, Preliminary Geologic Map of the Bodega Bay 30’ x 60’ Quadrangle, California: California Geological Survey, scale 1:100,000.
    Weber, K.M., List, J.H., and Morgan, K.L., 2005, An operational Mean High Water datum for determination of shoreline position from topographic lidar data: U.S. Geological Survey Open-File Report 2005-1027, accessed April 5, 2011, at http://pubs.usgs.gov/of/2005/1027/.
    Witter, R.C., Knudsen, K.L., Sowers, J.M., Wentworth, C.M., Koehler, R.D., Randolph, C.E., Brooks, S.K., and Gans, K.D., 2006, Maps of Quaternary Deposits and Liquefaction Susceptibility in the Central San Francisco Bay Region, California, U.S. Geological Survey Open-File Report 06-1037, scale 1:24,000.
    Date: 05-Oct-2017 (process 4 of 6)
    Added Distribution_Information section to metadata to facilitate data download. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
    Date: 05-Oct-2017 (process 5 of 6)
    Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
    Date: 26-Apr-2018 (process 6 of 6)
    Added keywords from Coastal and Marine Ecological Classification Standard (CMECS) to metadata. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    Polygons were primarily mapped by one of the following methods: (1) interpretation of 2-meter-resolution hillshaded bathymetry data from bathymetric lidar and sonar surveys (see Bathymetry Hillshade--Offshore Bodega Head, California, California, DS 781, for more information); (2) interpretation of 2-meter-resolution amplitude (backscatter) data from bathymetric sonar surveys (see BackscatterA_8101; BackscatterB_7125; BackscatterC_Swath--Offshore Bodega Head, California, DS 781, for more information); (3) interpretation of 2-meter interpretation of seismic-reflection-profile data (see field activity S-15-10-NC).
    Map Unit contact locations were interpreted typically at a scale of between 1:1,000 and 1:2,000 using the above base data. Bathymetric sonar and LiDAR data have a horizontal accuracy greater than the resolution of the base data.
    Map unit contacts were digitized by heads-up screen digitization of line data on 2-meter-resolution DEMs described above. Horizontal accuracy is estimated to be between 2 and 5 meters depending on how clearly contacts can be resolved.
    Most digitized positions on the map are estimated to have better than 5 m horizontal accuracy. There is no elevation data in the database.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Data are complete: no offshore features that could be accurately identified and represented at the compilation scale of 1:24,000 were eliminated or generalized. The smallest area represented is approximately 100 square meters. All geospatial database elements are attributed.
  5. How consistent are the relationships among the observations, including topology?
    Map elements were visually checked for overshoots, undershoots, duplicate features, polygon closure, and other errors by the lead authors and by the GIS technician(s) who created the digital database. Review drafts of the map were reviewed internally by at least two other geologists for consistency with basic geologic principles and general conformity to USGS mapping standards.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
If physical samples or materials are available, constraints on their on-site access are described in "WR CMG Sample Distribution Policy" at URL: http://walrus.wr.usgs.gov/infobank/programs/html/main/sample-dist-policy.html
Use_Constraints:
This information is not intended for navigational purposes.
Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data.
Acknowledge the U.S. Geological Survey in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.
This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    345 Middlefield Rd
    Menlo Park, CA
    USA

    (650) 329-4309 (voice)
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 26-Apr-2018
Metadata author:
U.S. Geological Survey, Coastal and Marine Geology Program
Attn: Stephen R. Hartwell
400 Natural Bridges Drive
Santa Cruz, CA
US

831-460-7814 (voice)
831-427-4748 (FAX)
shartwell@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/cal_state_waters/Geology_OffshoreBodegaHead_metadata.faq.html>
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