Preliminary soil-slip susceptibility maps, southwestern California

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Frequently anticipated questions:

What does this data set describe?

Preliminary soil-slip susceptibility maps, southwestern California
This data set maps the soil-slip susceptibility for several areas in southwestern California. Created using Environmental Systems Research Institute's ARC/INFO software, the data base consists of raster maps containing grid cells coded with soil- slip susceptibility values. In addition, the data set includes the following graphic and text products: (1) postscript graphic plot files containing the soil-slip susceptibility map, topography, cultural data, and a key of the colored map units, and (2) PDF and text files of the Readme (including the metadata file as an appendix) and accompanying text, and a PDF file of the plot files.
Intense winter rains commonly generated debris flows in upland areas of southwestern California. These debris flows initiate as small landslides referred to as soil slips. Most of the soil slips mobilize into debris flows that travel down slope at varying speeds and distances. The debris flows can be a serious hazard to people and structures in their paths. The soil-slip susceptibility maps identify those natural slopes most likely to be the sites of soil slips during periods of intense winter rainfall. The maps were largely derived by extrapolation of debris-flow inventory data collected from selected areas of southwestern California. Based on spatial analyses of soil slips, three factors in addition to rainfall, were found to be most important in the origin of soil slips. These factors are geology, slope, and aspect. Geology, by far the most important factor, was derived from existing geologic maps. Slope and aspect data were obtained from 10-meter digital elevation models (DEM). Soil-slip susceptibility maps at a scale of 1:24,000 were derived from combining numerical values for geology, slope, and aspect on a 10-meter cell size for 128 7.5' quadrangles and assembled on 1:100,000-scale topographic maps. The resultant maps of relative soil-slip susceptibility represent the best estimate generated from available debris-flow inventory maps and DEM data.
  1. How might this data set be cited?
    Morton, Douglas M., Alvarez, Rachel M.H., and Campbell, Russell H., 2003, Preliminary soil-slip susceptibility maps, southwestern California: U.S. Geological Survey Open-File Report 03-17, U.S. Geological Survey, Menlo Park, California.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -120.00446939
    East_Bounding_Coordinate: -116.8742505
    North_Bounding_Coordinate: 34.52044023
    South_Bounding_Coordinate: 32.49939779
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2003
    Not for use after June, 2003
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 22569 x 29031, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 11
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -117
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 10.0
      Ordinates (y-coordinates) are specified to the nearest 10.0
      Planar coordinates are specified in Meters
      The horizontal datum used is North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    Version 1.0 of the Preliminary Soil-Slip Susceptibility Maps, Southwestern California comprises seven ARC/INFO grids, la_sus, lb_sus, ocs_sus, sbern_sus, sd_sus, sa_sus, sbarb_sus, which contain soil-slip susceptibility values.
     Grid name   Quadrangle name
     la_sus      Los Angeles
     lb_sus      Long Beach
     ocs_sus     Oceanside
     sbern_sus   San Bernardino
     sd_sus      San Diego and El Cajon
     sa_sus      Santa Ana
     sbarb_sus   Santa Barbara
    The item names and definitions are the same for each raster data set and are as follows:
        1  VALUE                  4    10     B      -
        5  COUNT                  4    10     B      -
        9  SUSCODE                8     8     N      3
        1  MIN                    8    15     F      3
        9  MAX                    8    15     F      3
       17  MEAN                   8    15     F      3
       25  STDV                   8    15     F      3
    The item suscode contains the susceptibility values.
    Susceptibility values identified in each of the seven mapped areas (the Santa Barbara 100K sheet, the Los Angeles 100K sheet, the south half of the San Bernardino 100K sheet, the Long Beach 100K sheet, the Santa Ana 100K sheet, the Oceanside 100K sheet, and the San Diego and western El Cajon 100K sheets)
    Number corresponding to a susceptibility. Generally, the numbers can be interpreted as follows:
        6 through  999: low susceptibility
     1000 through 3250: moderate susceptibility
     3251 through 5000: high susceptibility
    0A value of 0 indicates the cell does not meet the criteria needed to fall into the low, moderate or high susceptibility categories.
    Range of values

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Douglas M. Morton
    • Rachel M.H. Alvarez
    • Russell H. Campbell
  2. Who also contributed to the data set?
    Geologic mapping and digital preparation of this report were sponsored jointly by (1) the National Cooperative Geologic Mapping Program of the U.S. Geological Survey, (2) the California Geological Survey, and (3) the Southern California Areal Mapping Project (SCAMP). The California Geological Survey graciously provided geologic map data and critical input.
  3. To whom should users address questions about the data?
    Douglas M. Morton
    U.S. Geological Survey, Western Region, Earth Surface Processes Team
    Project geologist
    U.S. Geological Survey
    Riverside, California
    United States of America

    (909) 276-6397 (voice)
    (909) 276-6295 (FAX)

Why was the data set created?

These data sets were derived to describe the relative soil-slip susceptibility for upland areas of southwestern California. Although released on a 1:100,000-scale topographic base, the data were derived at a scale of 1:24,000 and as such can be transferred from 1:100,000-scale to 1:24,000-scale without any loss of accuracy. The maps are not intended to be used at any scale larger than 1:24,000.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: Sep-2002 - 200301 (process 1 of 4)
    Process included mapping debris flows from several generations of aerial photographs in selected areas of southwestern California. Debris flows were transferred by inspection to 7.5' topographic quadrangle maps to produce debris flow inventory maps. Debris flow inventory maps were digitized in a GIS system (Arc/Info). Geologic data were obtained from digital geologic data bases from various sources. Digital elevation data were obtained from U.S. Geological Survey digital elevation models (DEM). Susceptibility values were the product of numerical values assigned to geologic map units, slope, and aspect.
    Date: 08-Jan-2003 (process 2 of 4)
    First draft of metadata created by Rachel Alvarez using FGDCMETA.AML ver. 1.2 05/14/98 on ARC/INFO data set
    Date: 13-Jan-2003 (process 3 of 4)
    Digital database review by Scott Graham.
    Date: 08-Jan-2003 (process 4 of 4)
    Creation of original metadata record Person who carried out this activity:
    U.S. Geological Survey
    Attn: Rachel M.H. Alvarez
    U.S. Geological Survey
    Riverside, California

    (909) 276-6397 (voice)
    (909) 276-6295 (FAX)
  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?
    The map meets national geologic map standards. The digital elevation data meet U.S. Geological National Digital Elevation Model standards.
  2. How accurate are the geographic locations?
    For accuracy information for DEM data refer to the U.S. Geological Survey Digital Elevation Models, Data User's Guide 5. Complete reference is in the explanatory text document.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    The map reflects the most accurate geologic map data and DEM data currently available to the U.S. Geological Survey.
  5. How consistent are the relationships among the observations, including topology?

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
This data base is not to be used at a scale larger than 1:24,000.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey Information Services
    Box 25286 Denver Federal Center
    Denver, Colorado

    (303) 202-4700 (voice)
    (303) 202-4693 (FAX)
  2. What's the catalog number I need to order this data set? USGS Open-File Report 03-17
  3. What legal disclaimers am I supposed to read?
    The U.S. Geological Survey (USGS) provides these geographic data "as is". The USGS makes no guarantee or warranty concerning the accuracy of information contained in the geographic data. The USGS further makes no warranties, either expressed or implied as to any other matter whatsoever, including, without limitation, the condition of the product, or its fitness for use lies entirely with the user. Although these data have been processed successfully on computers at the USGS, no warranty, expressed or implied, is made by the USGS regarding the use of these data on any other system, nor does the fact of distribution constitute or imply any such warranty.
    In no event shall the USGS have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of use of or reliance on the geographic data or arising out of the delivery, installation, operation, or support by USGS.
    These digital map databases, 1:100,000 scale, and any derivative maps thereof, is not meant to be used or displayed at any scale larger than 1:24,000 (e.g., 1:12,000).
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 10-Jun-2016
Last Reviewed: 13-Jan-2003
Metadata author:
Peter N Schweitzer
USGS Midwest Area
Collection manager, USGS Geoscience Data Clearinghouse,
Mail Stop 954
12201 Sunrise Valley Dr
Reston, VA

703-648-6533 (voice)
703-648-6252 (FAX)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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