Identification_Information:
  Citation:
    Citation_Information:
          Originator: V.E. Langenheim
          Originator: R.C. Jachens
          Originator: C.M. Wentworth
          Originator: R.J. McLaughlin
         Publication_Date: 2011
          Title: Preliminary Aeromagnetic and aeromagnetic-based geologic maps of the Coastal Belt, Franciscan Complex, northern California
          Geospatial_Data_Presentation_Form: point digital data
          Series_Information:
            Series_Name: Scientific Investigations Map
            Issue_Identification: 3188
          Publication_Information:
            Publication_Place: Menlo Park, CA
            Publisher: U.S. Geological Survey
            Online Linkage: http/pubs.usgs.gov/sim/3188
  Description:
    Abstract: New aeromagnetic data in aeromagnetic maps of the Coastal Belt, Franciscan Complex, northern California
      Digital Files:  The database includes an ASCII file 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 Firefly Aviation, Ltd.
  Time_Period_of_Content:
    Time_Period_Information:
      Range_of_Dates/Times:
        Beginning_Date:  2008
        Ending_Date:  2011
    Currentness_Reference:  publication date
   Status:
    Progress: Complete
    Maintenance_and_Update_Frequency: None planned
  Spatial_Domain:
    Bounding_Coordinates:
      West_Bounding_Coordinate: -124.3865
      East_Bounding_Coordinate: -122.7742
      North_Bounding_Coordinate: 40.61917
      South_Bounding_Coordinate: 38.32150
  Keywords:
    Theme:
      Theme_Keyword: magnetics
      Theme_Keyword: magnetic anomaly
    Place:
      Place_Keyword: northern California
      Place_Keyword: Coast Ranges
  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) Scientific investigations map
        Issue_Identification:  3188
      Publication_Information:
        Publication_Place:  Menlo Park, California
        Publisher:  U.S. Geological Survey
      Online_Linkage:  <URL:http://pubs.usgs.gov/sim/3188>

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: 2011
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: 61574
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: 200 m
    Attribute:
      Attribute_Label: lat_nad27
      Attribute_Definition: latitude coordinate
      Attribute_Value_Accuracy_Information:
        Attribute_Value_Accuracy: 200m
   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: 200 m
    Attribute:
      Attribute_Label: lat_nad27
      Attribute_Definition: latitude coordinate
      Attribute_Value_Accuracy_Information:
        Attribute_Value_Accuracy: 200m

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/sim/3188
  Process_Date:  2008-2011
    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
        (U.S. Geological Survey, 1985, 1994, 1996, 1997, 2005) and 
        the data were interpolated to a regular grid (Brigs, 1974) with cell dimensions of 200 m in both the X 
        and Y directions.an interval of 200 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 200 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.

        U.S. Geological Survey, 1985, Aeromagnetic map of the Redding 1 degree by 2 degree quadrangle, California: U.S. Geological Survey Open-File Report 85-757, scale 1:250,000.

        U.S. Geological Survey, 1994, Aeromagnetic map of Cape Mendocino and vicinity, California:  U.S. Geological Survey Open-File Report 94-444, scale 1:250,000.

        U.S. Geological Survey, 1996, Aeromagnetic map of the Clear Lake region on parts of the Santa Rosa and Ukiah 1 degree by 2 degree quadrangle, California: U.S. Geological Survey Open-File Report 96-691, scale 1:250,000.

        U.S. Geological Survey, 1997, Aeromagnetic map of Santa Rosa and vicinity on parts of Santa Rosa and San Francisco 1 degree by 2 degree quadrangles, California: U.S. Geological Survey Open-File Report 97-468, scale 1:250,000. 

        U.S. Geological Survey, 2005, Seven aeromagnetic surveys in California and Nevada:  A web site for distribution of data:  U.S. Geological Survey Open-File Report 2005-1328, [available at http://pubs.usgs.gov/of/2005/1328/ca-nev.html, last accessed February 2, 2011].


Metadata_Reference_Information:
  Metadata_Date: 20110501
  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