Gravity and ground magnetic data from selected traverses in the Amargosa desert and vicinity, Nevada and California

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Frequently anticipated questions:

What does this data set describe?

Gravity and ground magnetic data from selected traverses in the Amargosa desert and vicinity, Nevada and California
Maps of aeromagnetic data and a table of gravity station data embedded in the PDF report, not as separate files
  1. How might this data set be cited?
    Mankinen, Edward A., Sweetkind, Donald S., McKee, Edwin H., and Morin, Robert L., 2005, Gravity and ground magnetic data from selected traverses in the Amargosa desert and vicinity, Nevada and California: Open-File Report 2005-1444, Geological Survey (U.S.).

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -116.8333
    East_Bounding_Coordinate: -116.1667
    North_Bounding_Coordinate: 36.8333
    South_Bounding_Coordinate: 36
  3. What does it look like? (JPEG)
    Index map showing location of Amargosa Desert basin study area (outlined) and distribution of main geologic units of the surrounding region, (489 x 580 pixels)
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2003
    ground condition
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Entity Point (152)
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0001667. Longitudes are given to the nearest 0.0001667. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is World Geodetic System 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.
  7. How does the data set describe geographic features?
    Principal facts of gravity stations
    Station name Textual identifiers without distinct scientific significance
    Range of values
    Observed gravity
    Range of values
    Free air gravity anomaly
    Range of values
    Terrain inner zone correction
    Inner-zone terrain corrections (zones A, B, C, and D of Hayford and Bowie, 1912), which are necessary to account for variations in topography near a gravity station, were obtained using a program developed by Spielman and Ponce (1984).
    Terrain correction (total)
    Range of values
    Bouguer gravity anomaly
    Range of values
    Isostatic gravity anomaly
    Range of values
    Geographic latitude of station
    Range of values
    Units:decimal degrees
    Geographic longitude of station
    Range of values
    Units:decimal degrees

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Mankinen, Edward A.
    • Sweetkind, Donald S.
    • McKee, Edwin H.
    • Morin, Robert L.
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Edward A Mankinen
    345 Middlefield Road
    Mail Stop 937
    Menlo Park, CA

    650-329-4669 (voice)
    650-329-4664 (FAX)

Why was the data set created?

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: 2003 (process 1 of 2)
    Gravity data were obtained using a LaCoste and Romberg meter (USGS meter G8) and observed gravity values were referenced to the International Gravity Standardization Net 1971 (ISGN 71) gravity datum (Morelli, 1974). Gravity observations were tied to two ISGN 71 base stations (Harris and others, 1989); the original Beatty post office (BPO), now the Death Valley visitor station, and DUNE, west of the junction of U.S. Highway 95 and Nevada State Highway 29 in Amargosa Valley. The observed gravity value given for BPO in Harris and others (1989) has been revised to 979,566.45 mGal (D.A. Ponce, USGS, written communication, 1997).
    Observed gravity at each station was adjusted by assuming a time-dependent linear drift between readings of a base station at the start and finish of each daily survey. This adjustment compensates for drift in the instruments spring. All gravity data and their associated parameters are given in Table 1. Observed gravity values are considered accurate to about 0.05 mGal based on repeat measurements over several mountain calibration loops (Barnes and others, 1969; Ponce and Oliver, 1981). Gravity data were reduced using standard gravity corrections (Harris and others, 1989) and a reduction density of 2670 kg/m3. Inner-zone terrain corrections (zones A, B, C, and D of Hayford and Bowie, 1912), which are necessary to account for variations in topography near a gravity station, were obtained using a program developed by Spielman and Ponce (1984). The calculations use digitized topography in a digital elevation model (DEM) and a procedure by Plouff (1977). A regional isostatic field was calculated using an Airy-Heiskanen (Heiskanen and Vening Meinesz, 1958) model for local compensation of topographic loads (Simpson and others, 1983, 1986). This model assumes a crustal thickness of 25 km, a crustal density of 2670 kg/m3, and a 400 kg/m3 density contrast between the crust and mantle. This regional isostatic field was subtracted from the complete Bouguer anomaly, thus removing longwavelength variations in the gravity field that are inversely related to topography. The resulting isostatic residual gravity anomaly, therefore, is a reflection of local density distributions within middle to upper crustal levels. The isostatic residual gravity anomaly for the Amargosa Valley study area, incorporating the 152 new gravity observations from Table 1, is shown in figure 4. The new gravity stations were established along the same traverses as the ground magnetic profiles described in the following section and were intended to complement those data.
    Date: 05-Jun-2008 (process 2 of 2)
    Creation of original metadata record Person who carried out this activity:
    Peter N Schweitzer
    12201 Sunrise Valley Drive
    Reston, VA

    703-648-6533 (voice)
    703-648-6252 (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?
    Locations of gravity stations were determined using differential GPS, with surveyed benchmarks used for control and are accurate to within about 0.1 m, both horizontally and vertically
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  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
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? USGS Open-File Report 2005-1444
  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.
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 23-Feb-2015
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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