Principal facts for gravity stations in the western arm of the Black Rock Desert, Nevada

The U.S. Geological Survey (USGS) is a party to joint interagency Memorandums of Understanding with the Bureau of Land Management (BLM) and the U.S. Bureau of Mines (USBM) to coordinate resource assessments and evaluations of BLM-administered lands. Resource assessments of BLM Resource Areas, which are conducted by the USGS, assist the BLM in meeting inventory and evaluation, resource-management planning, and other management requirements of the Federal Land Policy and Management Act of 1976. This report is part of a resource assessment of BLM-administered land in northwest Nevada and northeast California. An earlier report, which summarizes the geology and its relation to resources (Doebrich, 1996), serves as a foundation for the interpretative discussion in the present report. The 1:2,000,000 map scales of figures 3 and 5 in the presesent report match the map scales of Doebrich (1996).

Section: Contentsmentioning

confidence: 99%

Resource assessment of the Bureau of Land Management's Winnemucca District and Surprise Resource Area, northwest Nevada and northeast California; gravity map and interpretation

Plouff¹

1997

“…Subsets with NGDC source numbers 3507,3578, and 3598 (table 2) were excluded because they do not fonr useful clusters with ties to other stations, and sources for their elevations and reliabilities of their local gravity base stations are unknown. Subsets in Nevada from the U.S. Geological Survey with source numbers 2235,4787,4788,4834,4869,4933,5018,5019,5020,5675,5869,5962,6948,6976,7358,7567,7838, and 7942 will be discussed in later sections of this report Only one set of data from the U.S. Geological Survey, source #2179 (Mabey, 1960), are retained as part of the NGDC set, inasmuch as no raw data or principal facts have been found for these data. Within the limitation of standard deviations that exceed 0.5 mGal for numerous ties (Plouff, 1977b, p.35;Plouff and others, 1976, p.5;Wagini, 1985, p. 15;and Plouff, 1994, p. 14), no consistent change of observed gravity could be applied to NGDC source #2179.…”

Section: Data From the National Geophysical Data Centermentioning

confidence: 99%

“…Gravity surveys were conducted by the U.S. Geological Survey as part of geologic evaluations of areas with potential geothermal resources (Peterson and Dansereau, 1975;Plouff and Conradi, 1975;Griscom and Conradi, 1976;Pe^.rson and Hassemer, 1977;Peterson and Hoover, 1977;Peterson and Kaufmann, 1978a, b, and c;Schaefer and Maurer, 1980;and Duffrin and others, 1985). The difference of observed gravity between values for the NGBN and IGSN-71 datums at the DMA base station in Gerlach, Nevada is reflected by the 13.79-mGal (table 4) datum shift applied to obtain NGDC sources #4834 (Peterson and Dansereau, 1975) and to obtain sources #5018, #5020, and #5019 (Peterson and Kaufmann, 1978a, b, and c).…”

Section: Geothermal Studiesmentioning

confidence: 99%

“…This error persisted in data sets of Snyder and others (1982) and NGDC source #4735. Schaefer and Maurer (1980) participated in a geothermal study in the western arm of the Black Rock Desert, Nevada (files BLACKLOV.ISN and BLACKVYA.ISN). The DMA subtracted 12.79 mGal from their listed values of observed gravity to convert to the IGSN-71 datum for NGDC source #5869.…”

Section: Geothermal Studiesmentioning

confidence: 99%

“…Therefore, I subtracted 1.0 rr Gal from values of observed gravity in source #5869. I replaced the source #5869 by " B" in station names but did not recover original station numbers from Schaefer and Maurer (1980). I corrected an incorrectly typed gravity reading on a field sheet (D.H. Schaefer, written commun., 1986) to correct an error of 700 units (67.55 mGal) for helicopter station "B93" (originally "BRK22"), which is not included in the 1991 version of NGDC source #5869.…”

Section: Geothermal Studiesmentioning

confidence: 99%

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Principal facts and field observations for gravity data in and adjacent to the Bureau of Land Management's Winnemucca District and Surprise Resource Area, northwest Nevada and northeast California

Plouff¹

1996

COMPILATION METHODSSteps to improve quality during the compilation of existing gravity data were to delete duplicate data, to correct or delete erroneous data, and to evaluate the accuracy of accepted data. Duplicate data could not be easily identify when previous compilers modified values of observed gravity, modified locations, or copied earlier data into their sets and then substituted different station names. The pattern of two sets of sequence numbers at associated data points ofter could be recognized except in cases where a later compiler modified locations or sorted data points by their latitude and then replaced original station numbers with numerical sequence numbers. Unless a less accurate data point is close! ' surrounded by data points of a less accurate data set or the data set with generally higher accuracy apparently cipied the less accurate data point, the less accurate data point was discarded.Data points with the same station names as other data points or without a station name, which occurred in subsets of data from the National Geophysical Data Center (table 2), were assigned unique station names. Data points located near spot elevations or bench marks, near cultural features such as roads or marked section corners, or arranged along regularly-spaced lines or grids generally were accepted with minor modifications. The last method for identifying data points to be rejected, corrected, or accepted was to look for conspicuous disagreements (forming one-station "bnllseye"

Gravity data for the state of Nevada on magnetic tape

Saltus¹

1988

Gravity data assembled for a state gravity map to be published by the Nevada Bureau of Mines are available from the EROS data center on magnetic tape. The first 18 files of the tape contain principal facts for individual data points, organized by 1° x 2° quadrangle. The approximately 71,000 individual data points are from numerous sources including the Defense Mapping Agency data base and U.S. Geological Survey files. Each data record contains geographic position, observed gravity, terrain correction, Bouguer gravity anomaly (p = 2.67 g/crn3), and isostatic residual anomaly (Airy Heiskanen, T = 25 km, A/? = 0.4 g/cm3). The 19th and 20th data files are 2 km square grids of complete Bouguer and isostatic residual gravity values based on the data in the preceding files. The 9-track magnetic tape is written at 1,600 bytes-per-inch (BPI) in ASCII format with an 80-character record and 4,000-character (50 record) block size. Gravity sources These Nevada gravity data consist primarily of data from the Defense Mapping Agency (DOD) data base (available from the National Geophysical and Solar-Terrestrial Data Center, Boulder, Colorado 80303). Additional data from U.S. Geological Survey (USGS) files in Denver, Colorado and Menlo Park, California are included. Most of the USGS data are documented in published Bouguer gravity anomaly maps and principal facts reports for the following 1° x 2° quadrangles in Nevada (see appendix for source DOD references