Identification_Information: Citation: Citation_Information: Originator: V.E. Langenheim, J.G. Davidson, M.L. Anderson, and H.R. Blank, Jr Publication_Date: 1999 Title: Principal facts for gravity stations and physical property measurements in the Lake Mead 30 x 60 minute quadrangle, Nevada and Arizona Edition: rev 1.0 Publication_Information: Publication_Place: U.S. Geological Survey, Menlo Park, CA Publisher: U.S. Geological Survey Online_Linkage: http://wrgis.wr.usgs.gov/open-file/of99-435 Description: Abstract: Gravity data were compiled, collected, and edited for the Lake Mead 30 x 60 minute quadrangle, Nevada and Arizona. Density and magnetic susceptibility measurements were made on more than 250 rock samples to provide physical property information for interpreting potential-field anomalies. Purpose: To provide basic geophysical information to regional mapping and hydrologic studies Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Victoria Langenheim Contact_Organization: U.S. Geological Survey Contact_Address: Address: 345 Middlefield Rd. MS 989 City: Menlo Park State_or_Province: CA Postal_Code: 94025 Country: USA Address_Type: mailing and physical address Contact_Voice_Telephone: 650-329-5313 Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -115.0 East_Bounding_Coordinate: -114.0 North_Bounding_Coordinate: 36.5 South_Bounding_Coordinate: 36.0 Native_Data_Set_Environment: data was stored and analysed on a SUN Ultra4000 UNIX platform Status: Progress: Preliminary report Maintenance_and_Update_Frequency: none planned Keywords: Place: Place_Keyword: Southeast Nevada, Lake Mead, Muddy Mountains, western Arizona Theme: Theme_Keyword: gravity, density, isostatic anomaly, magnetic property Access_Constraints: none Use_Constraints: none Data_Quality_Information: Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Accuracy of the point data is roughly 40m, as well as the data can be located on a 1:24,000-scale topographic map Vertical_Positional_Accuracy: Vertical_Positional_Accuracy_Report: Accuracy of the point data vary; most of the elevations are accurate to 10 feet or less. In some of the more mountainous areas, the accuracy may fall to 20 to 40 feet. Attribute_Accuracy: Attribute_Accuracy_Report: Observed gravity data are accurate to 0.05 mGal; reduced anomalies are accurate to 1-2 mGal. Data are more accurate in the valleys than in the mountains because of uncertainties in elevation and in the terrain correction. Grain density measurements accurate to 0.01 g/cm3; susceptibility measurements to 0.01 x 10-3 cgs units. Logical_Consistency_Report: see open-file report Completeness_Report: Dataset based on geophysical analysis. see open-file report. Lineage: Source_Information: Source_Citation: Citation_Information: Originator: Saltus, R.W. Publication_Date: 1988 Title: Gravity data for the state of Nevada on magnetic tape Series_Information: Series_Name: U.S. Geological Survey Open-file Report 88-433 Edition: first edition Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geodetic_Model: Horizontal_Datum_Name: Geographic NAD27 Ellipsoid_Name: CLARKE 1866 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Definition: Point_Type Overview_Description: Entity_and_Attribute_Overview: The data files are in ASCII format. The gravity data define point data with information as follows: STATION NAME (a8) An alphanumeric combination of up to 8 characters used for station identification; LAT (f3.0,f6.3) Latitude in degrees and minutes, to 0.01 minute; LON (f4.0,f6.3) Longitude in degrees and minutes, to 0.01 minute; ELEV (f8.2) Elevation, to 0.1 ft; OG (f10.3) Observed gravity, to 0.01 mGal; FAA (f9.3) Free-air anomaly to 0.01 mGal; SBA (f8.3) Simple Bouguer anomaly to 0.01 mGal; ITC (f7.3) Inner terrain correction for a density of 2.67 g/cc, to 0.01 mGal, followed by a letter denoting the extent of the correction. "Z" indicates computer terrain correction from the station out to 166.7 km with inner terrain correction out to D zone; TC (f7.3) Total terrain correction from the station to 166.7 km for a density of 2.67 g/cc, to 0.01 mGal; TC CODE (a1) Letter denoting the extent of the correction, according to the Hayford-Bowie template (e.g. 'D' means 590 meters); CBA (f8.3) Complete Bouguer anomaly reduced for a density of 2.67 g/cc, to 0.01 mGal; ISO (f8.3) Isostatic residual anomaly values assuming an Airy model for isostatic compensation of topographic loads. This model assumes a a crustal thickness of 25 km, a topographic load density of 2.67 g/cc, and a density contrast across the base of the model crust of 0.4 g/cc; ISO-COR (f8.3) Isostatic anomaly corrected for effects of Lake Mead. The density and susceptibility data define point data with information as follows: STATION NAME: alphanumeric combination of up to 10 characters used for station identification (some of these coincide with gravity station locations); LATITUDE, in decimal degrees (north); LONGITUDE, in decimal degrees (west); GRAIN DENSITY, in grams per cubic centimeter; DRY BULK DENSITY, in grams per cubic centimeter; SATURATED BULK DENSITY, in grams per cubic centimeter; MAGNETIC SUSCEPTIBILITY, in 10-3 cgs units; and ROCK TYPE, description of hand sample. Overview_Description: Entity_and_Attribute_Overview: point data representing gravity data and density and susceptibility measurements Metadata_Reference_Information: Metadata_Date: 19990818 Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata