Geologic Map of the Saint Lawrence Island, Alaska

U.S. Geological Survey Scientific Investigations Map 3146
By: William W. Patton, Jr., Frederic H. Wilson, and Theresa A. Taylor


The growth in the use of Geographic Information Systems (GIS) has highlighted the need for digital geologic maps that have been attributed with information about age and lithology. Such maps can be conveniently used to generate derivative maps for manifold special purposes such as mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This report is part of a series of integrated geologic map databases that will eventually cover Alaska.

The digital geologic map presented here is in a standardized format as ARC/INFO export files and as ArcView shape files. The files named SLgeol contain geologic polygons and line (contact) attributes. Data tables that relate the map units to detailed lithologic and age information accompany these GIS files. The map is delivered as a 1:250,000-scale quadrangle file.


The digital datasets that form the basis for this product were compiled and created using existing published and unpublished data. Alaska spatial and text databases in this series are all linked through the use of a field, called nsaclass, that is related to the age and lithology of the map units contained on each map. (Note: database field names are in italics). Two fields which have been added to the polygon attribute table (PAT) and also in the text databases, nsaclass and qclass, are used to store information that correlates individual map units between sources. Nsaclass is used to make regional unit assignments and generally reflects a known or an inferred correlation of map units. For example, all "Surficial deposits, undivided" are assigned an nsaclass code of 100. The schema for nsaclass was developed as regional maps throughout Alaska were compiled and reflects an iterative process. As new or additional information became available, the nsaclass code for a particular map unit may have changed, either to reflect lumping or finer separation of map units. Nsaclass is used to cover the entire geologic time scale, whereas the similar qclass is restricted to and provides finer detail for Quaternary map units. A source field and a field called nsamod are also added. Nsamod provides information with respect to hydrothermal alteration or contact metamorphism of a map unit, either for the entire unit or on an individual polygon basis. In this way, the nsaclass field needs only to store the primary map unit information. Source is a coded reference citation, indicating the manuscript or other source for the information. The format for source is XX###, where XX is the two letter quadrangle code (CAPITAL letters) and ### is a three digit number (using leading zeros) to indicate a specific reference. Finally, a field called lith2 is in the PAT as a scratch field; no uniform schema has been developed for this field.

The standardized attribute tables were generated by extracting information from the legends of the source maps, in this case, the DMU for this map. The standardized attribute tables record an abstracted map unit description, lithologic and age information, and references.

The spatial databases are provided in the native UTM projection of the source as well as geographic coordinates. The UTM projection parameters are described in the metadata (note that the datum is NAD’27). Because of limitations of the UTM projection for regional maps, provided here are the parameters for the Albers Equal Area projection commonly used in Alaska for regional or state-wide products:

Projection: Albers equal Area
Horizontal datum: NAD’27
Spheroid: Clarke, 1866
1st Standard parallel: 55 degrees North
2nd Standard parallel: 65 degrees North
Central meridian: 154 degrees West
Latitude of projection origin: 50 degrees North
Units: meters
False easting (meters): 0
False northing (meters): 0

A "data-structure" file provides additional information about this product. [PDF]

ArcView files can be viewed with the free viewer, ArcExplorer, which can be downloaded from

Supplemental attribute TABLES FOR Saint Lawrence Island geologic map

FileMaker Pro files directory

file size: 4.3 Mb

Comma-separated ASCII files directory

file size: 1.1 Mb

DBF files directory

file size: 4.0 Mb

Filemaker Pro runtime application

file size: 40.1

PDF files of the geologic map and text

Saint Lawrence Island geologic map

file size: 4.4 Mb

Pamphlet for Saint Lawrence Island geologic map (includes age table)

file size: 414 kb


Metadata as HTML

file size: 40 kb

Metadata as FAQ (HTML)

file size: 29 kb

metadata as text

file size: 28 kb

metadata as XML

file size: 22 kb

ARC/INFO shadeset (wpgcmykg.shd)

file size: 114 kb

ARC/INFO lineset (geology.lin)

file size: 13 kb

ArcGIS style sheet for polygons

file size: 924 kb

ArcGIS style sheet for arcs

file size: 1,224 kb

Saint Lawrence Island Quadrangle

UTM zone 2
Arc Export (.e00) files

UTM projection

Geographic coordinates


file size: 891 kb


file size: 891 kb


file size: 13 kb


file size: 13 kb

ArcView shapefiles (.shp)

file size: 429 kb

file size: 470 kb

file size: 3 kb

file size: 3 kb

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Page Last Modified: February 9, 2012 (mfd)