This map is a statewide summary of magmatic (igneous) rocks
grouped into geologic units that can be portrayed
cartographically at 1:2,500,000.
This dataset consists of a polygon coverage and associated attribute
data derived from the 1994 map "Latest Cretaceous and
Cenozoic magmatic rocks of Alaska" compiled by E.J. Moll-Stalcup,
D.A. Brew, and T.L. Vallier. This map was originally published (
at 1:2,5000,0000) as Plate 5 in Volume G-1, "The Geology of
Alaska", edited by G. Plafker and H.C. Berg, and published by the
Geological Society of America (GSA). Volume G-1 (The Geology of
Alaska) is one of a series published by GSA for the Decade of
North American Geology (DNAG), and is often referred to as the
This digital dataset includes all 44 magmatic rock units from the
original map, including dredged and outcrop sampled areas. It
includes attributes for rock age (6 groups), composition
(8 groupings), ranges and combinations of age and composition;
and the location of hypabyssal or agglomeratic/tuffaceous units
(TYPE = H or T)
This coverage is not intended to be a complete representation of
the printed map. It does NOT include the following features:
locations of calderas or volcanoes; inset maps of magmatic
provinces; or explanatory text (introduction and references).
This coverage is intended to provide digital features (polygons)
representing generalized magmatic rock units in Alaska for use in
small-scale spatial analysis (statewide) with similar coverages
such as other geologic units, vegetation types, soils, etc.
The linework was digitized in 1997 from a paper copy of the 1994 map at
the U.S. Geological Survey's Alaska Section (Geologic Division) facilities in
Anchorage, AK. The original Transverse Mercator projection of the map (Central
Meridian: 100*W; Scale factor: 0.926; Reference ellipsoid:(6371204m, 63712004m)) was
converted to an Albers equal-area coverage in ARC/INFO (version 7.1.2). The
resulting coverage did not align exactly with an Albers equal-area coverage of the
Alaskan coastline, so a rubber-sheeting operation was performed using points
along the coastline and major rivers to match an Albers equal area projection.
Map unit (polygon) locations and attributes were checked by the person responsible for
the digitizing, and spot-checked by one reviewer, by comparing a printed copy
of the coverage to the published map. Metadata were collected using document.aml
v. 7.1.1, distributed by ESRI, Inc.
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
This coverage should not be copied or distributed without its
associated metadata file. Intended use is at small scales (e.g.
statewide, 1:2,500,000 etc.) only; enlargements of this data to
scales greater than that at which they were originally compiled can
lead to misinterpretation of data. The U.S. Geological Survey
(Dept. of Interior) should be acknowledged as the data source in
products derived from these data. Use of these data is not
restricted; however, organizations, agencies, units of government
or other users are responsible for its appropriate application.