Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database

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Frequently anticipated questions:

What does this data set describe?

Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database
Alameda County is located at the northern end of the Diablo Range of Central California. It is bounded on the north by the south flank of Mount Diablo, one of the highest peaks in the Bay Area, reaching an elevation of 1173 meters (3,849 ft). San Francisco Bay forms the western boundary, the San Joaquin Valley borders it on the east and an arbitrary line from the Bay into the Diablo Range forms the southern boundary. Alameda is one of the nine Bay Area counties tributary to San Francisco Bay. Most of the country is mountainous with steep rugged topography. Alameda County is covered by twenty-eight 7.5' topographic Quadrangles which are shown on the index map (alq_quad or Sheet 2).
The Quaternary deposits in Alameda County comprise three distinct depositional environments. One, forming a transgressive sequence of alluvial fan and fan-delta facies, is mapped in the western one-third of the county. The second, forming only alluvial fan facies, is mapped in the Livermore Valley and San Joaquin Valley in the eastern part of the county. The third, forming a combination of Eolian dune and estuarine facies, is restricted to the Alameda Island area in the northwestern corner of the county.
  1. How might this data set be cited?
    Helley, E.J., and Graymer, R.W., 1997, Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database: U.S. Geological Survey Open-File Report 97-97.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -122.38
    East_Bounding_Coordinate: -121.38
    North_Bounding_Coordinate: 38.0
    South_Bounding_Coordinate: 37.38
  3. What does it look like?
    http://pubs.usgs.gov/of/1997/0097/pdf/alqmap.pdf (PDF)
    PDF representation of the geologic map sheet
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 1997
    publication date
  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: California state plane coordinate system
      SPCS_Zone_Identifier: 3426
      Planar coordinates are encoded using coordinate pair
      Planar coordinates are specified in meters
  7. How does the data set describe geographic features?
    ARC/INFO export files	Description of coverage
    at_sp-py.e00           Quaternary deposits of the Altamont quadrangle
    bh_sp-py.e00           Byron Hot Springs quadrangle
    cf_sp-py.e00           Clifton Court Forebay quadrangle
    cm_sp-py.e00           Cedar Mtn quadrangle
    cr_sp-py.e00           Calaveras Reservoir quadrangle
    du_sp-py.e00           Dublin quadrangle
    em_sp-py.e00           Eylar Mtn quadrangle
    ha_sp-py.e00           Hayward quadrangle
    hp_sp-py.e00           Hunters Point quadrangle
    lc_sp-py.e00           La Costa Valley quadrangle
    lt_sp-py.e00           Las Trampas Ridge quadrangle
    lv_sp-py.e00           Livermore quadrangle
    mb_sp-py.e00           Mt Boardman quadrangle
    md_sp-py.e00           Mt Day quadrangle
    mp_sp-py.e00           Milpitas quadrangle
    ms_sp-py.e00           Mendenhall Springs quadrangle
    mv_sp-py.e00           Mountain View quadrangle
    mw_sp-py.e00           Midway quadrangle
    ne_sp-py.e00           Newark quadrangle
    ni_sp-py.e00           Niles quadrangle
    oe_sp-py.e00           Oakland East quadrangle
    ow_sp-py.e00           Oakland West quadrangle
    ri_sp-py.e00           Richmond quadrangle
    rp_sp-py.e00           Redwood Point quadrangle
    sl_sp-py.e00           San Leandro quadrangle
    ta_sp-py.e00           Tassajara quadrangle
    alq_quad.e00           Index map of quadrangles in Alameda County
    alq_corr.e00           Correlation table for the units in this map database
    al_dr-sp.e00           Drainage base map
    al_cu-sp.e00           Cultural base map
    al_topo-sp.e00         Topographic contours base map
    Entity_and_Attribute_Detail_Citation: http://pubs.usgs.gov/of/1997/0097/pdf/alqgeo.pdf

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • E.J. Helley
    • R.W. Graymer
  2. Who also contributed to the data set?
    Carl M. Wentworth, Todd T. Fitzgibbon, and Geoffrey A. Phelps graciously provided assistance with Alacarte and ARC/INFO. The scanning and initial editing of the digital maps of some of the quadrangles was done by the following: Heather Schoonover (Midway, Newark), Marjorie Lucks (Livermore), Scott Graham (Altamont), Lisa Gerhardt (San Leandro), Jennifer Tarsoly (Hayward), Carolyn Randolph (Hunters Point, Redwood Point), Molly Burgett (Oakland West), Michelle Roberts (Niles, La Costa Valley). Earl E. Brabb provided much helpful advice and feedback, as well as arranging for material support for the project.
  3. To whom should users address questions about the data?
    Graymer, Russell W
    Mail Stop 975, USGS
    345 Middlefield Road
    Menlo Park, CA

    650-329-4988 (voice)

Why was the data set created?

To provide to the public a digital geologic map database of the Alameda county and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin counties, California.

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: unknown (process 1 of 2)
    Geological units were mapped on 1:24,000 scale U.S. Geological Survey topographic maps using 1939 black and white aerial photographs showing the county before much development had taken place. The mapping was supplemented with 1:12,000- and 1:24,000-scale color aerial photography flown in 1965 and 1974 respectively. The mapping was also aided by observations made on turn of the century topographic maps at 1:62,500-scale with 25 foot (7.6 m) contour intervals. These maps were most useful in recognizing natural stream channels which have since been modified. The position of water boundaries, the stream channel to water transition, the length and position of mapped stream channels (see below), the distribution of artificial levees, and the apparent distribution of artificial fill were plotted to conform with the most recent 1:24,000 scale topographic maps.
    Mapping units were delineated by: 1) landform morphology, 2) relative topographic position, 3) relative preservation of surface morphology, 4) tonal contrasts on aerial photographs, 5) relative soil profile development (compiled from the U.S. Soil Conservation Service, 1917), and 6) other features such as differences in vegetation density and type. Landform morphology refers to the shape of a particular landscape element. Examples are the distinctive conical shape of alluvial fans and the shape of levees that usually border active stream channels, sloping away from them to blend into flat basin deposits. Other criteria listed in the description of geological units are also used to distinguish one element from another, but they are particularly useful for delineating units within a specific landscape element. A surface on an alluvial fan, for example, might be differentiated from another because of its higher topographic position, greater drainage density, and stronger soil profile development. Geologic units defined this way are called allostratigraphic units (American Association of Petroleum Geologists Bulletin, 1983).
    Digital Compilation
    The geologic map information was digitized from stable originals of the geologic maps at 1:24,000 scale. The author manuscripts (pencil on mylar) were scanned using a Altek monochrome scanner with a resolution of 800 dots per inch. The scanned images were vectorized and transformed from scanner coordinates to projection coordinates with digital tics placed by hand at quadrangle corners. The scanned lines were edited interactively by hand using ALACARTE, color boundaries were tagged as appropriate, and scanning artifacts visible at 1:24,000 were removed.
    Base Maps
    Base Map layers were prepared from scale-stable printing negatives of the U.S. Geological Survey San Francisco (1978 edition), Stockton (1989 edition), Palo Alto (1983 edition), and San Jose (1978 edition) 1:100,000 topographic maps, which have a 50 meter contour interval. Scanned and vectorized images were transformed from scanner coordinates to projection coordinates with digital tics placed by hand at map corners. The images were then trimmed interactively by hand using ALACARTE to conform to the area of the geologic coverages, and the four portions were combined. Small mismatches at the boundaries caused by slight differences in the original scans remain in the three base map coverages. These base map layers are digital images but no information other than location is attached to the lines.
    Date: 14-Aug-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?
  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?
    No bedrock units have been mapped; bedrock outcrop is simply labeled "br". Other geologic features, such as folds and faults, have not been mapped. A few large landslides are shown, but this map does not show most of the landslides in the area.
  5. How consistent are the relationships among the observations, including topology?
    This digital map database, compiled from previously unpublished data, and new mapping by the authors, represents the general distribution of surficial deposits in Alameda County and surrounding areas.

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)
    USGS Information Services
    Box 25286, Denver Federal Center
    Denver, Colorado

    1-888-ASK-USGS (voice)
    1-303-202-4695 (FAX)
  2. What's the catalog number I need to order this data set? US Geological Survey Open-File Report 97-97
  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 "Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital 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.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: Quaternary geologic units and base map information in format ARCE (version 7.x) Size: 19.5
      Network links: http://pubs.usgs.gov/of/1997/0097/al_q1.tar.Z
    • Cost to order the data: none

Who wrote the metadata?

Last modified: 10-Jun-2016
Metadata author:
Peter N Schweitzer
USGS Midwest Area
Collection manager, USGS Geoscience Data Clearinghouse, http://geo-nsdi.er.usgs.gov/
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)

This page is <https://geo-nsdi.er.usgs.gov/metadata/open-file/97-97/metadata.faq.html>
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