Identification_Information: Citation: Citation_Information: Originator: Mankinen, Edward A. Originator: Sweetkind, Donald S. Originator: McKee, Edwin H. Originator: Morin, Robert L. Title: Gravity and ground magnetic data from selected traverses in the Amargosa desert and vicinity, Nevada and California Publication_Date: 2005 Series_Information: Series_Name: Open-File Report Issue_Identification: 2005-1444 Publication_Information: Publisher: Geological Survey (U.S.) Online_Linkage: http://pubs.usgs.gov/of/2005/1444/ Description: Abstract: Maps of aeromagnetic data and a table of gravity station data embedded in the PDF report, not as separate files Time_Period_of_Content: Time_Period_Information: Single_Date/Time: Calendar_Date: 2003 Currentness_Reference: ground condition Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -116.8333 East_Bounding_Coordinate: -116.1667 North_Bounding_Coordinate: 36.8333 South_Bounding_Coordinate: 36 Keywords: Place: Place_Keyword_Thesaurus: Augmented FIPS 10-4 and FIPS 6-4 Place_Keyword: f06027 = Inyo Place_Keyword: f32023 = Nye Theme: Theme_Keyword_Thesaurus: General glossary for mineral resources spatial data Theme_Keyword: Portable Document Format Theme: Theme_Keyword_Thesaurus: USGS Thesaurus Theme_Keyword: aeromagnetic surveying Theme_Keyword: geologic structure Theme_Keyword: geophysics Theme_Keyword: gravimeter measurement Theme_Keyword: gravitational field (earth) Theme_Keyword: magnetic field (earth) Theme_Keyword: maps and atlases Access_Constraints: none Use_Constraints: none Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Edward A Mankinen Contact_Organization: USGS WR SW GD Contact_Address: Address_Type: mailing address Address: 345 Middlefield Road Mail Stop 937 City: Menlo Park State_or_Province: CA Postal_Code: 94025 Country: USA Contact_Voice_Telephone: 650-329-4669 Contact_Facsimile_Telephone: 650-329-4664 Contact_Electronic_Mail_Address: emank@usgs.gov Browse_Graphic: Browse_Graphic_File_Name: http://pubs.usgs.gov/of/2005/1444/images/indexmap.jpg Browse_Graphic_File_Description: 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) Browse_Graphic_File_Type: JPEG Data_Quality_Information: Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: 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 Lineage: Process_Step: Process_Description: 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 instrument‰Ûªs 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. Process_Date: 2003 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Point Point_and_Vector_Object_Information: SDTS_Terms_Description: SDTS_Point_and_Vector_Object_Type: Entity Point Point_and_Vector_Object_Count: 152 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.0001667 Longitude_Resolution: 0.0001667 Geographic_Coordinate_Units: decimal degrees Geodetic_Model: Horizontal_Datum_Name: World Geodetic System 1984 Ellipsoid_Name: WGS 84 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.257 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: 2005-1444.dbf Entity_Type_Definition: Principal facts of gravity stations Attribute: Attribute_Label: STAT_NAME Attribute_Definition: Station name Attribute_Domain_Values: Unrepresentable_Domain: Textual identifiers without distinct scientific significance Attribute: Attribute_Label: ELEV Attribute_Definition: Elevation Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 621.90 Range_Domain_Maximum: 861.10 Attribute_Units_of_Measure: meters Attribute: Attribute_Label: OBS_GRAV Attribute_Definition: Observed gravity Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 979581.160 Range_Domain_Maximum: 979628.740 Attribute_Units_of_Measure: mGal Attribute_Measurement_Resolution: 0.01 Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 0.05 Attribute_Value_Accuracy_Explanation: 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) Attribute: Attribute_Label: FREE_AIR Attribute_Definition: Free air gravity anomaly Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -55.00 Range_Domain_Maximum: -1.60 Attribute_Units_of_Measure: mGal Attribute_Measurement_Resolution: 0.01 Attribute: Attribute_Label: TER_HAND Attribute_Definition: 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). Attribute_Domain_Values: Enumerated_Domain: Enumerated_Domain_Value: 0.0D Enumerated_Domain: Enumerated_Domain_Value: 0.1D Enumerated_Domain: Enumerated_Domain_Value: 0.2D Attribute: Attribute_Label: TER_TOT Attribute_Definition: Terrain correction (total) Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 0.20 Range_Domain_Maximum: 1.50 Attribute: Attribute_Label: BOUG_ANOM Attribute_Definition: Bouguer gravity anomaly Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -132.20 Range_Domain_Maximum: -90.50 Attribute_Units_of_Measure: mGal Attribute_Measurement_Resolution: 0.01 Attribute: Attribute_Label: ISOST_ANOM Attribute_Definition: Isostatic gravity anomaly Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -19.60 Range_Domain_Maximum: 23.90 Attribute_Units_of_Measure: mGal Attribute_Measurement_Resolution: 0.01 Attribute: Attribute_Label: LATITUDE Attribute_Definition: Geographic latitude of station Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 36.317777780 Range_Domain_Maximum: 36.750277780 Attribute_Units_of_Measure: decimal degrees Attribute: Attribute_Label: LONGITUDE Attribute_Definition: Geographic longitude of station Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -116.70972220 Range_Domain_Maximum: -116.30138890 Attribute_Units_of_Measure: decimal degrees Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: USGS Information Services Contact_Address: Address_Type: mailing Address: Box 25286, Denver Federal Center City: Denver State_or_Province: Colorado Postal_Code: 80255-0046 Country: USA Contact_Voice_Telephone: 1-888-ASK-USGS Contact_Facsimile_Telephone: 1-303-202-4695 Contact_Electronic_Mail_Address: infoservices@usgs.gov Resource_Description: USGS Open-File Report 2005-1444 Distribution_Liability: 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. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: Shapefile Format_Version_Number: 1.0 Format_Information_Content: Principal facts of gravity stations File_Decompression_Technique: unzip Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: http://pubs.usgs.gov/of/2005/1444/data/2005-1444.zip Fees: none Metadata_Reference_Information: Metadata_Date: 20080605 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Peter N Schweitzer Contact_Organization: USGS ER GD Contact_Position: Geologist Contact_Address: Address_Type: mailing address Address: 12201 Sunrise Valley Drive City: Reston State_or_Province: VA Postal_Code: 20192-0002 Country: USA Contact_Voice_Telephone: 703-648-6533 Contact_Facsimile_Telephone: 703-648-6252 Contact_Electronic_Mail_Address: pschweitzer@usgs.gov Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998