Landslides in Alameda County, California, A Digital Database Extracted from Preliminary Photointerpretation Maps of Surficial Deposits by T.H. Nilsen in USGS Open-File Report 75-277

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Frequently anticipated questions:

What does this data set describe?

Landslides in Alameda County, California, A Digital Database Extracted from Preliminary Photointerpretation Maps of Surficial Deposits by T.H. Nilsen in USGS Open-File Report 75-277
All or part of 25 7.5-minute quadrangles identifying 8465 Landslides largely slow-moving slides and earth flows in Alameda County, California, have been converted to a digital-map database, compiled at 1:24,000 scale and plotted at 1:62,500 scale, that can be acquired from the U.S. Geological Survey over the Internet or on magnetic tape.
  1. How might this data set be cited?
    Roberts, Sebastian, Roberts, Michelle A., Brennan, Eileen M., Pike, Richard J., and Roberts, Sebastian, 1999, Landslides in Alameda County, California, A Digital Database Extracted from Preliminary Photointerpretation Maps of Surficial Deposits by T.H. Nilsen in USGS Open-File Report 75-277: U.S. Geological Survey Open-File Report 99-0504.

    Online Links:

    ARC export coverage, ARCVIEW shape files, and supporting ARC/INFO files. Each individual file <5MB.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -122.4
    East_Bounding_Coordinate: -121.5
    North_Bounding_Coordinate: 37.9
    South_Bounding_Coordinate: 37.5
  3. What does it look like? (PDF)
    A PDF representation of the map with map keys for the landslides in Alameda County, California.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 1999
    Preliminary photointerpretation of surficial deposits (1975) and publication of digital database (1999).
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: map
  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):
      • Entity point
      • Complete chain
      • GT-polygon composed of chains
    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
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest unknown
      Ordinates (y-coordinates) are specified to the nearest unknown
      Planar coordinates are specified in meters
      The horizontal datum used is NAD27.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    Type of contact or boundary (Source: OFR-99-0504)
    Line type (Source: OFR-99-0504)
    contact, certainObserved contact
    county boundaryBoundary around the counties
    map boundaryBoundary of mapped area
    water boundaryBoundary of inland waters
    Landslide deposit (Source: OFR-99-0504)
    Polygon type (Source: OFR-99-0504)
    lslandslide deposit
    lsulandslide deposit, identification uncertain
    nlsnot landslide deposit
    grid of quadrangle boundaries (Source: OFR-99-0504)
    quadrangle names (see Entity_and_Attribute_Overview) (Source: OFR-99-0504)
    point features for small landslides for the La Costa Valley Quadrangle (Source: OFR-99-0504)
    Point type (Source: OFR-99-0504)
    unattributedno attributes
    ?unknown attributes
    Strike of landslide (Source: OFR-99-0504)
    Range of values
    25 USGS Quadrangles in the Coverage GRDPYS.SHP.PAT:
    Briones Valley
    Oakland East
    Las Trampas Ridge
    Byron Hot Springs
    Clifton Court Forebay (formerly Bethany)
    San Leandro
    Hayward, Dublin
    La Costa Valley
    Mendenhall Springs
    Cedar Mountain
    Lone Tree Creek
    Calaveras Reservoir
    Mt. Day
    Eylar Mountain
    Mt. Boardman
    Oakland West
    Hunters Point
    Redwood Point
    Mountain View
    For more information on coverages see the pamphlet included with the downloads.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Sebastian Roberts
    • Michelle A. Roberts
    • Eileen M. Brennan
    • Richard J. Pike
    • Sebastian Roberts
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Sebastian Roberts
    US Geological Survey
    Menlo Park, CA

Why was the data set created?

To provide information to the public on the landslide probability by studying previous landslide deposits. The study sought to provide, in forms understandable and usable by non-specialists, the earth-science information needed to solve problems related to growth and development in the nine-county, 7,400-square-mile San Francisco Bay Region.

How was the data set created?

  1. From what previous works were the data drawn?
    Nilsen and others, 1975 (source 1 of 1)
    Nilsen, T.H., Bartow, J.A., Frizzell, V.A., and Sims, J.D., 1975, Preliminary photointerpretation maps of landslide and other surficial deposits of 56 7.5-minute quadrangles in the southeastern San Francisco Bay region, Alameda, Contra Costa, and Santa Clara Counties, California: U.S. Geological Survey Open-File Report 75-0277.

    Type_of_Source_Media: paper
    Source_Scale_Denominator: 24000
    A 1:24,000-scale photointerpretive inventory of (predominantly) old and ancient landslides measuring over 200 feet across and other surficial geologic deposits in the southeastern part of the Bay Region. The area included by the database was mapped by Nilsen only.
  2. How were the data generated, processed, and modified?
    (process 1 of 2)
    The digital compilation was derived from linework inked directly by T.H. Nilsen on 25 USGS Mylar greenline 7.5-minute (1:24,000-scale) quadrangles that cover Alameda County and were used to photographically reproduce the lines on his 1975 and 1976 maps. The linework for each greenline was scanned (400 dots per inch), converted from raster to vector form, imported into ARC/INFO, hand edited to remove all information save landslides, and combined into a single digital file. Landslide outlines were adjusted as needed to align across quadrangle boundaries. The base map for the landslide data comprises topography, drainage, and culture from 1:125,000-scale USGS Bay Region Topographic Sheets (Aitken 1997). A 1:62,500-scale map image was derived from the digital database.
    Date: 21-Jul-2000 (process 2 of 2)
    Creation of original metadata record Person who carried out this activity:
    Jennifer Lenz
    US Geological Survey
    12201 Surise Valley Drive, Mail Stop 918
    Reston, VA

    703-648-6974 (voice)
    703-648-6560 (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?
    Date of photography: Modifications of the landscape that have occurred since the date the aerial photographs were taken are not shown on this map. Thus, landslide deposits and large artificial fills that postdate the photography are not delineated, although some of the topographic base maps were photorevised in 1968 and do show the extent of urbanization to that date.
    Urbanization: Surficial geologic features can be obscured in urbanized areas by (1) modification of the natural landscape by grading (leveling, cutting, filling, or terracing), and (2) man-made structures that cover the natural land surface. Less than 10 percent of the area included in this map has been extensively urbanized.
    Forest cover: Surficial deposits may be difficult to recognize in forested areas, so that such areas may be mapped less accurately than grass-covered areas. Many landslide deposits may be impossible to recognize on slopes covered with dense stands of tall trees. Less than 15 percent of the area included in this map is densely forested.
    Quality of photography: The accuracy of the map varies directly with the clarity and contrast of the aerial photographs used. Accordingly, haze, cloud cover, or poor sun angles make photointerpretation more difficult; also, the steepness of the topography and the location and extent of shaded areas-affect the usefulness of individual photographs. In general, however, the photographs used to prepare this map are of excellent quality.
    Scale of maps and photography: Landslide and other surficial deposits less than about 200 feet long are not shown because they are too small to be clearly identified on the photographs or clearly portrayed on the topographic base map. In addition, no attempt has been made to show the numerous small areas covered by artificial fill along highways, railroads and airstrips, in cemeteries, in populated and farming areas, or near quarries and mines, even though some are more than 200 feet in longest dimension.
    Problems in interpretation: Mapping of surficial deposits by photointerpretation alone presents a number of difficult problems, some of which can be resolved only through field checking.

    Problems that are especially difficult include:
    (1) distinguishing terrace-shaped slump-type landslide deposits from alluvial terrace deposits where both are located adjacent to stream courses;
    (2) recognizing bedrock cropping out beneath surficial deposits, especially where a creek or stream has cut down through the overlying surficial deposits to expose bedrock along the stream bed;
    (3) determining boundaries between adjacent surficial deposits that laterally grade into or interfinger with one another without leaving any easily discernible topographic boundaries, e.g., the downstream gradation of alluvial terrace deposits into alluvial deposits;
    (4) recognizing landslide deposit boundaries--whereas the upslope boundary is commonly defined by an easily recognized scarp, the toe or downslope boundary is seldom well defined and is difficult to locate exactly;
    (5) recognizing stable masses of bedrock within landslide deposits, especially where the bedrock may appear only as a large block within the surrounding landslide deposit; and
    (6) distinguishing between irregular or hummocky topography caused either by variations in the erosional resistance of bedrock or by the erosion of landslide deposits.
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Information on the hazard is incomplete; no slope failures since 1966 are shown. The many landslides from the severe winters of 1982, 1983, and 1998 (Coe and others, 1999) are absent. Detailed mapping by private consultants also is not included here, nor are landslides mapped more recently by the California Division of Mines and Geology (Majmundar, 1991a, b; 1995a, b). Debris flows are absent from the database.
  5. How consistent are the relationships among the observations, including topology?
    Although the information in this database has not been updated or amended beyond that in the original publication, we are releasing it in digital form because it is the only systematic landslide-inventory that covers Alameda County in its entirety. Users are cautioned that these 35- to 40-year-old data have shortcomings in addition to caveats cited in the original map text (see Part I, below).

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
Use_Constraints: none
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey Information Services
    Box 25248, Denver Federal Center
    Denver, CO

    1-888-ASK-USGS (voice)
    1-303-202-4693 (FAX)
  2. What's the catalog number I need to order this data set? US Geological Survey Open-File Report 99-0504
  3. What legal disclaimers am I supposed to read?
    This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    This database, identified as 'Landslides in Alameda County, California, a digital database extracted from preliminary photointerpretation maps of surficial deposits by T.H. Nilsen in USGS Open-file Report 75-277', has been approved for release and publication by the Director of the USGS. Although this database has been reviewed and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. This database is released on condition that neither the USGS nor the U.S. Government may be held liable for any damages resulting from its use.
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 05-Feb-2016
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 for Digital Geospatial Metadata (FGDC-STD-001-1998)

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