Isopachs--Punta Gorda to Point Arena, California

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What does this data set describe?

Title: Isopachs--Punta Gorda to Point Arena, California
This part of DS 781 presents data for the isopachs of the Punta Gorda to Point Arena, California, region. The vector data file is included in the "," which is accessible from As part of the USGS's California State Waters Mapping Project, a 50-m grid of sediment thickness for the seafloor within the 3-nautical mile limit between Punta Gorda and Point Arena was generated from seismic-reflection data collected between 2010 and 2012, and supplemented with geologic structure (fault) information following the methodology of Wong (2012). Reference Cited: Wong, F. L., Phillips, E.L., Johnson, S.Y., and Sliter, R.W., 2012, Modeling of depth to base of Last Glacial Maximum and seafloor sediment thickness for the California State Waters Map Series, eastern Santa Barbara Channel, California: U.S. Geological Survey Open-File Report 2012-1161, 16 p. (available at
Additional information about the field activities from which these data were derived is available online at:
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology.
  1. How might this data set be cited?
    Beeson, Jeff W., Johnson, Samuel Y., and Cochran, Susan A., 2019, Isopachs--Punta Gorda to Point Arena, California: Data Series DS 781, U.S. Geological Survey, Reston, VA.

    Online Links:

    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: -124.452888
    East_Bounding_Coordinate: -123.702617
    North_Bounding_Coordinate: 40.300181
    South_Bounding_Coordinate: 39.020333
  3. What does it look like? (JPEG)
    Isopachs for the region between Point Sur and Point Arguello
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 09-Aug-2010
    Ending_Date: 25-Sep-2012
    ground condition at time seismic data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: shapefile
  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):
      • String (1332)
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 10
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.00000
      Latitude_of_Projection_Origin: 0.00000
      False_Easting: 500000.0
      False_Northing: 0.00
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 50.0
      Ordinates (y-coordinates) are specified to the nearest 50.0
      Planar coordinates are specified in Meters
      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378137.00.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    lines of equal thickness (Source: standard sedimentology)
    Internal feature number (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Feature geometry. (Source: Esri) Coordinates defining the features.
    sequential feature number (Source: this study) sequential feature numbers
    line of equal thickness (Source: this study) lines of equal thickness

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Jeff W. Beeson
    • Samuel Y. Johnson
    • Susan A. Cochran
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: PCMSC Science Data Coordinator
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)

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 aid in assessments and mitigation of geologic hazards in the Punta Gorda to Point Arena 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?
    seismic (source 1 of 2)
    Beeson, J.W., Johnson, S.Y., Goldfinger, C., and Hartwell, S.R., 2016, Marine geophysical data—Point Arena to Cape Mendocino: U.S. Geological Survey, online.

    Online Links:

    Type_of_Source_Media: SEG-Y
    digital seismic data from Punta Gorda to Point Arena used to interpret subsurface geologic structure
    faults (source 2 of 2)
    Beeson, Jeff W., and Johnson, Samuel Y., 2019, Faults—Punta Gorda to Point Arena, California: U.S. Geological Survey data release doi: 10.5066/P9PNNI9H, U.S. Geological Survey, online.

    Online Links:

    Type_of_Source_Media: shapefile
    faults from Punta Gorda to Point Arena were used to interpret subsurface geologic structure
  2. How were the data generated, processed, and modified?
    Date: 2017 (process 1 of 3)
    Water bottom (seabed) and depth to base of the Last Glacial Maximum (LGM) horizons were digitized from seismic-reflection data using Kingdom Suite software. The difference between the two horizons was exported from Kingdom Suite for every shot point as XY coordinates (UTM Zone 10) and two-way travel time (TWT). The thickness was determined by applying a sound velocity to the TWT of 1,500 m/sec in water and 1,600 m/sec velocity in sediment, resulting in sediment thickness values. Data sources used in this process:
    • seismic
    • faults
    Data sources produced in this process:
    • SedimentThicknessPoints
    Date: 2017 (process 2 of 3)
    XY locations and sediment thickness values Z were imported to ArcGIS format as points and interpolated to a preliminary surface with TopoRaster from which isopachs (thickness contours) were extracted at 3.5 m intervals, with an additional contour at 0.25 m. Further refinement of this sediment thickness map and the isopach shapefile (see was accomplished through several iterations of manual editing to incorporate geology and fault information following the methodology of Wong (2012; see Data sources used in this process:
    • SedimentThicknessPoints
    Data sources produced in this process:
    • Isopachs
    Date: 19-Oct-2020 (process 3 of 3)
    Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
  3. What similar or related data should the user be aware of?
    Beeson, Jeff W., and Originator: Samuel Y. Johnson, 2019, Offshore shallow structure and sediment distribution, Punta Gorda to Point Arena, northern California: Open-File Report 2019-1072, U.S. Geological Survey, Reston, VA.

    Online Links:

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

  1. How well have the observations been checked?
    The data points from seismic-reflection profiles are dense along tracklines (about 1-2 m apart) and sparse between tracklines (typically 1,000 m apart). 50-m cell size for interpolation is better supported along track than between.
  2. How accurate are the geographic locations?
    The sparker position may vary as much as 20 m from the navigation reference on the vessel.
  3. How accurate are the heights or depths?
    Estimated to be approximately 1 m, along the track lines where data is well constrained, but may be much greater in areas where interpolation occurred.
  4. Where are the gaps in the data? What is missing?
    Sediment thickness data points exported from Kingdom Suite profiling software were processed within the California 3-nmi limit.
  5. How consistent are the relationships among the observations, including topology?
    No formal logical accuracy tests were conducted. All vector geometry and attributes are present.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator of the dataset and in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
  2. What's the catalog number I need to order this data set? The .zip file ( includes the .cpg, .dbf, .prj, .sbn, .sbx, .shp, .shp.xml, and .shx files, as well as FGDC-compliant metadata for the Isopach data layer in the Punta Gorda to Point Arena region of California.
  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?
  5. What hardware or software do I need in order to use the data set?
    The downloadable data file has been compressed with the "zip" command and can be unzipped with Winzip (or other tool) on Windows systems. To utilize these data, the user must have software capable of uncompressing the WinZip file and importing and viewing an Esri ArcMap TIFF. Users should download the ArcGIS project file,, a compressed (with the "zip" command) version of the ArcMap document (.mxd) that has all the data layers loaded in the table of contents for "Punta Gorda to Point Arena" map region and has all the data symbolized as on the map sheets. Download and save this ArcGIS project file, including all data layers, to the directory the user has created for this GIS.

Who wrote the metadata?

Last modified: 19-Oct-2020
Metadata author:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Attn: PCMSC Science Data Coordinator
2885 Mission Street
Santa Cruz, CA

831-427-4747 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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