anch_boreholes_font_point borehole and well log locations bcc_elmendorf_region approximate surface extent of Elmendorf-age outwash deposits bcclimit_polyline approximate subsurface limit of thick, fine-grained facies of Bootlegger Cove Formation (BCF) geology_region geologic unit polygons
Combellick, R.A., 1999, Simplified Geologic Map and Cross Sections of Central and East Anchorage, Alaska: Preliminary Interpretive Report PIR 1999-1, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, Alaska - USA.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.000032
Ordinates (y-coordinates) are specified to the nearest 0.000032
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.978698.
|Codeset Source:||Alaska Division of Geological & Geophysical Surveys <http://www.dggs.alaska.gov/metadata/PIR1999-1_codeset.pdf>|
Unique alphanumeric code assigned to each borehole.
Unique alphanumeric code assigned to each grid square.
|1||Hollow-stem borehole without standard penetration test|
|2||Hollow-stem borehole with standard penetration test (SPT)|
|3||Cone penetration test (CPT)|
|4||Solid stem auger (no cores or SPT)|
|6||Pit or trench|
|Range of values|
|1||Digitized from 1:24,000-scale topographic map|
|2||Digitized from 1:10,000 or larger scale map with UTM or lat/long coordinates|
|4||Determined by differentially corrected GPS|
|5||Coordinates provided by driller|
|6||Center of 4th quarter section (2-1/2 acre square) within which hole was drilled; actual location unknown|
|7||Center of 3rd quarter section (10 acre square) within which hole was drilled; actual location unknown|
|9||Location within land parcel or project site is unknown|
|Range of values|
Unique index number assigned to each borehole.
This research was partially supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number 1434-HQ-96-GR-02713. Additional Acknowledgments: Geology modified from Schmoll and Dobrovolny (1972). Digital cartography by R.A. Combellick and S.M. Weems, with suggestions by A.L. Schell. R.D. Reger and P.J. Haeussler provided helpful comments on the draft map and cross sections.
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The purpose of this project was to acquire existing surficial geologic and subsurface data, both borehole and well-log, and incorporate it into an updated and simplified geologic map and cross sections of central and east Anchorage.
Schmoll, H.R., and Dobrovolny, E., 1972, Generalized Geologic Map of Anchorage and Vicinity, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-787-A.
Data sources used in this process:
Geologic point, line, and polygon data were derived by digitizing the geologic map by Schmoll and Dobrovolny (1972), then combining selected units. The location of the 30-ft isopach of Bootlegger Cove clay depicted in the layer pir1999-1_bcclimit_polyline was estimated by identifying boreholes in which soft, fine-grained deposits of the Bootlegger Cove formation have a continuous or nearly continuous thickness of 30 ft (10 m) or more. Hence this isopach is interpreted and its horizontal accuracy is unknown. With the exception of digital water-well logs, for which geographic positions were provided by the supplying agency, all borehole locations in the layer pir1999-1_anch_boreholes_font_point were digitized in GIS from project site maps provided with the drilling reports. The scale and detail of these site maps are highly variable, resulting in variation in accuracy of the digitized locations. See the Horizontal_Positional_Accuracy_Report below.
The accuracy of geologic unit boundaries in the layers pir1999-1_geology_region and and pir1999-1_bcc_elmendorf_region depend on the accuracy of the original geologic map by Schmoll and Dobrovolny (1972) and the accuracy of digitizing. In the layer pir1999-1_anch_boreholes_font_point, the attribute "location_method" is a code indicating the method by which the borehole or well log locations were determined (see Entity_and_Attribute_Information).
Measurements of boreholes and wells for the attribute "FT" in the layer pir1999-1_anch_boreholes_font_point were taken from the original driller's reports, which do not contain information about measurement accuracy. Depth is generally reported as the total length of drill string below ground surface, including the auger and all drill rods.
This dataset includes geospatial information related to geologic map units and borehole localities.
Polygon topology present and clean on appropriate data. Other data are line, point, or annotation data and do not require topologic relationships.
Are there legal restrictions on access or use of the data?
- This report, map, and/or dataset are available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
- Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. User specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys.
Preliminary Interpretive Report 1999-1
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