Identification_Information: Citation: Citation_Information: Originator: V.E. Langenheim Originator: P.L. Hill Publication_Date: 2010 Title: Preliminary Aeromagnetic Map of Joshua Tree National Park and Vicinity, Southern California Geospatial_Data_Presentation_Form: point digital data Series_Information: Series_Name: Open-File Report Issue_Identification: 2010-1070 Publication_Information: Publication_Place: Menlo Park, CA Publisher: U.S. Geological Survey Online Linkage: http://pubs.usgs.gov/of/2010/1070/ Description: Abstract: Aeromagnetic mosaic map of Joshua Tree National Park and vicinity, southern California Digital Files: The database includes two ASCII files containing new aeromagnetic data and two ASCII files with point locations of the local maximum horizontal gradient derived from the aeromagnetic data. This metadata file describes the horizontal gradient locations derived from new and existing aeromagnetic data. Purpose: Aeromagnetic map identifies magnetic features as a basis for geophysical interpretations; the gradients help define the edges of magnetic sources. Supplemental_Information: This database updates geophysical information originally presented in smaller-scale formats and includes detailed aeromagnetic data collected by EON Geosciences, Inc. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2008 Ending_Date: 2009 Currentness_Reference: publication date Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -116.50 East_Bounding_Coordinate: -115.25 North_Bounding_Coordinate: 34.17 South_Bounding_Coordinate: 33.61 Keywords: Theme: Theme_Keyword: magnetics Theme_Keyword: magnetic anomaly Place: Place_Keyword: Southern California Place_Keyword: Eastern Transverse Ranges Place_Keyword: Joshua Tree National Park Access_Constraints: none Use_Constraints: Uses of this digital data should not violate the spatial or attribute resolution of the data. Although the digital form of the data stores location and attribute values to several decimals of precision, the data is subject to the accuracy and precision inherent in the data due to data collection and processing limitations. Where this data is used in combination with other data, the precision and accuracy of the resulting dataset is limited by the precision and accuracy of the input datasets. Acknowledgement of the U.S. Geological Survey is appreciated for products derived from these data. Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Victoria Langenheim Contact_Organization: U.S. Geological Survey Contact_Position: geophysicist Contact_Address: Address_Type: physical address Address: 345 Middlefield Rd. City: Menlo Park State_or_Province: CA Postal_Code: 94025 Country: USA Contact_Voice_Telephone: 650-329-5313 Contact_Electronic_Mail_Address: zulanger@usgs.gov Native_Data_Set_Environment: Geosoft Oasis Montaj Native_Data_Set_Environment: ARC/INFO versions 9.0., 9.1, 9.2, and 9.3 Geophysical data was stored and analyzed on a SUN Ultra4000 UNIX platform Geospatial_Data_Presentation_Form: ascii digital data (horizontal magnetic gradients) Series_Information: Series_Name: U.S. Geological Survey (USGS) Open-File Report Issue_Identification: 2010-1070 Publication_Information: Publication_Place: Menlo Park, California Publisher: U.S. Geological Survey Online_Linkage: Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: maximum horizontal gradient values are reported to 0.000001 nT/km Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: accuracy should be within 200 meters (grid size that gradient was calculated from) Lineage: Process_Step: Process_Description: Maximum horizontal gradient is calculated from the magnetic potential grid derived from the aeromagnetic map/grid Process_Date: 2009 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: 12958 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.0001 Longitude_Resolution: 0.001 Geographic_Coordinate_Units: Decimal degrees Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1929 Ellipsoid_Name: Clarke 1866 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: grad_big.xyz Attribute: Attribute_Label: maximum horizontal gradient Attribute_Definition: location of local maximum horizontal gradient from magnetic potential of aeromagnetic grid (larger than the mean of the entire area) Attribute: Attribute_Label: lon_nad27 Attribute_Definition: longitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250 m Attribute: Attribute_Label: lat_nad27 Attribute_Definition: latitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250m Entity_Type: Entity_Type_Label: grad_small.xyz Attribute: Attribute_Label: maximum horizontal gradient Attribute_Definition: location of local maximum horizontal gradient from magnetic potential of aeromagnetic grid (less than the mean of the entire area) Attribute: Attribute_Label: lon_nad27 Attribute_Definition: longitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250 m Attribute: Attribute_Label: lat_nad27 Attribute_Definition: latitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250m Distribution_Information: Distributor: U.S. Geological Survey Resource_Description: Downloadable Data Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ASCII Transfer_Size: 483988 Network_Resource_Name: http://pubs.usgs.gov/of/2010/1070 Process_Date: 2007-2010 Process_Step: Process_Description: Geophysical mapping The locations of local maximum horizontal gradient of the magnetic field were derived using a compilation of the newly flown aeromagnetic data (this report) and previously published aeromagnetic data. The aeromagnetic data were compiled from existing publications (Grauch, 1984; LK&B Resources, Inc., Sweeney, 2002, U.S. Geological Survey, 1981, 1983, 1985, 1990) and the data were interpolated to a regular grid (Briggs, 1974) with cell dimensions of 250 m in both the X and Y directions, an interval of 250 m. The magnetic base levels were then adjusted to a common magnetic datum, with a 1-km gap separating the various surveys. The interpolated data were mathematically transformed to pseudogravity anomalies (Baranov, 1957). The pseudogravity field was upward continued a distance of 100 m and then subtracted from the original pseudogravity field. Horizontal maximum gradients were then calculated from the residual pseuodgravity field (Blakely and Simpson, 1986). The two files are grad_big.axyz and grad_small.axyz. Baranov, V.I., 1957, A new method for interpretation of aeromagnetic maps--pseudo-gravimetric anomalies: Geophysics, v. 22, p. 359-383. Blakely, R.J., and Simpson, R.W., 1986, Approximating edges of source bodies from magnetic or gravity anomalies: Geophysics, v. 51, p. 1494-1498. Briggs, I., 1974, Machine contouring using minimum curvature: Geophysics, v. 39, no. 1, p. 39-48. Grauch, V.J.S., 1984, Aeromagnetic map of the Eagle Mountains area, Riverside County, California: U.S. Geological Survey Open-File Report 84-502, scale 1:62,500. LK&B Resources, Inc., 1980, NURE aerial gamma-ray and magnetic reconnaissance survey, Colorado-Arizona area, Salton Sea NI 11-9, El Centro NI11-12, Phoenix NI 12-7, Ajo NI12-10, and Lukeville NH 12-1, quadrangles: U.S. Department of Energy, Grand Junction Office Report GJBX-012(80), 5 vols. Sweeney, R.E., 2002, Six aeromagnetic surveys in California, Nevada, and Arizona: A web site for distribution of data: U.S. Geological Survey Open-File Report 02-486 (http:// pubs.usgs.gov/of/2002/ofr-02-486). U.S. Geological Survey, 1981, Aeromagnetic map of the Needles 1-degree by 2-degree quadrangle, California and Arizona: U.S. Geological Survey Open-File Report 81-085, scale 1:250,000. U.S. Geological Survey, 1983, Aeromagnetic map of the Salton Sea area, California: U.S. Geological Survey Open-File Report 83-664, scale 1:250,000. U.S. Geological Survey, 1985, Aeromagnetic map of the Palen area, Riverside County, California: U.S. Geological Survey Open-File Report 85-281, scale 1:62,500. U.S. Geological Survey, 1990, Aeromagnetic map of parts of the San Diego, Santa Ana, and adjacent 1-degree by 2-degree quadrangles, California: U.S. Geological Survey Open-File Report 90-206, scale 1:250,000. Metadata_Reference_Information: Metadata_Date: 20100520 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Victoria Langenheim Contact_Organization: U.S. Geological Survey Contact_Position: geophysicist Contact_Address: Address_Type: mailing and physical address Address: 345 Middlefield Rd. City: Menlo Park State_or_Province: CA Postal_Code: 94025 Contact_Voice_Telephone: 650-329-5313 Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998 Metadata_Time_Convention: local time Metadata_Extensions: Online_Linkage: http://www.esri.com/metadata/esriprof80.html Profile_Name: ESRI Metadata Profile