GIS data notes for PRELIMINARY GEOLOGIC MAP OF THE ISLAND OF SAIPAN, COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS
 
by David J. Weary and William C. Burton
U.S. Geological Survey Open-File Report 2011-1234

Abstract: This map provides an update and reinterpretation of the geology of the island of Saipan. The geology of the island was previously documented in 1956 in U.S. Geological Survey (USGS) Professional Paper 280-A by Preston E. Cloud, Jr., and others. This report includes a geologic map at a scale of 1:25,000. The fieldwork for this project was performed in 2006 and 2007. 

Process:  (1) Geologic data (including bedrock polygons, faults, and bedding and joint point) measurements were digitized from a scanned copy of the Cloud and others (1956) geologic map. (2) Point field data, collected via GPS-enabled handheld computers by the authors in 2006 and 2007, were added to the set of digital data from Cloud and others (1956). (3) The composited new and old data were plotted onto a modern topographic base map (1999 USGS 1:25,000-scale topographic map of the island of Saipan. (4) After consultation between the two authors, contact lines and fault lines were adjusted to conform to observed data and the geologic interpretation. 
The data were created as a personal geodatabase in ArcGIS v.10 and then exported to ESRI shapefile format.

Projection of GIS data and base map: WGS_1984_UTM_Zone_55N, units = meters

Base map:  A digital raster graphic (DRG) image of the USGS 1999, topographic map of Saipan, scale 1:25,000, is provided. This DRG is georegistered in the same projection as the shapefile data.

Shapefiles provided:

SaipanFaults: This data set includes lines delineating faults mapped on the island of Saipan.

SaipanGeoPolys: This data set includes polygons delineating geologic map units on the island of Saipan.

SaipanGeoPts: This data set includes point locations of bedding and structural measurements made by the authors and by Cloud and others (1956).

SaipanTtOverlays: This data set consists of polygons delineating areas of the tuffaceous and marly lithofacies of the Tagpochau Limestone (map units Ttv and Ttm) as well as areas of brecciation within the Tagpochau Limestone. The intent for use of this data set is to provide delineation for overlay patterns to be displayed in a layer over the polygons of Tagpochau Limestone (map unit Ttl) delineated in the separate SaipanGeoPolys.shp file.

Metadata:  A separate metadata file, in both .txt and .xml formats, is provided for each shapefile. ArcMap users will be able to access the metadata directly from the *.xml file associated with each shapefile.

These data can be downloaded from the USGS at:  http://pubs.usgs.gov/of/2011/1234