Geologic map of the Chewelah 30' x 60' quadrangle, Washington and Idaho

The data set for the Chewelah 30' X 60' quadrangle has been jointly
prepared by the U.S. Geological Survey Mineral Resource Program, the
Southern California Areal Mapping Project (SCAMP), and the Washington
Division of Geology and Earth Resources, as part of an ongoing effort to
utilize a Geographical Information System (GIS) format to create regional
digital geologic databases. These regional databases are being developed
as contributions to the National Geologic Map Data Base of the National
Cooperative Geologic Mapping Program of the USGS.

The digital geologic map database for the Chewelah 30' X 60' quadrangle
has been created as a general-purpose data set that is applicable to
other land-related investigations in the earth and biological sciences.
For example, it can be used for mineral resource evaluation studies,
animal and plant habitat studies, and soil studies in the Colville and
Kaniksu National Forests. The database is not suitable for site-specific
geologic evaluations.

This data set maps and describes the geology of the Chewelah 30' X 60'
quadrangle, Washington and Idaho. Created using Environmental Systems
Research Institute's ARC/INFO software, the data base consists of the
following items: (1) a map coverage containing geologic contacts and
units, (2) a point coverage containing site-specific geologic structural
data, (3) two coverages derived from 1:100,000 Digital Line Graphs (DLG);
one of which represents topographic data, and the other, cultural data,
(4) two line coverages that contain cross-section lines and unit-label
leaders, respectively, and (5) attribute tables for geologic units
(polygons), contacts (arcs), and site-specific data (points). In
addition, the data set includes the following graphic and text products:
(1) A PostScript graphic plot-file containing the geologic map,
topography, cultural data, and two cross sections, and on a separate
sheet, a Correlation of Map Units (CMU) diagram, an abbreviated
Description of Map Units (DMU), modal diagrams for granitic rocks, an
index map, a regional geologic and structure map, and a key for point and
line symbols; (2) PDF files of the Readme text-file and expanded
Description of Map Units (DMU), and (3) this metadata file.

The geologic map database contains original U.S. Geological Survey data
generated by detailed field observation and by interpretation of aerial
photographs. The map was compiled from geologic maps of eight 1:48,000
15' quadrangle blocks, each of which was made by mosaicing and reducing
the four constituent 7.5' quadrangles. These 15' quadrangle blocks were
mapped chiefly at 1:24,000 scale, but the detail of the mapping was
governed by the intention that it was to be compiled at 1:48,000 scale.
The compilation at 1:100,000 scale entailed necessary simplification in
some areas and combining of some geologic units. Overall, however,
despite a greater than two times reduction in scale, most geologic detail
found on the 1:48,000 maps is retained on the 1:100,000 map. Geologic
contacts across boundaries of the eight constituent quadrangles required
minor adjustments, but none significant at the final 1:100,000 scale.

The geologic map was compiled on a base-stable cronoflex copy of the
Chewelah 30' X 60' topographic base and then scribed. The scribe guide
was used to make a 0.007 mil-thick blackline clear-film, which was
scanned at 1200 DPI by Optronics Specialty Company, Northridge,
California. This image was converted to vector and polygon GIS layers
and minimally attributed by Optronics Specialty Company. Minor
hand-digitized additions were made at the USGS. Lines, points, and
polygons were subsequently edited at the USGS by using standard
ARC/INFO commands. Digitizing and editing artifacts significant enough
to display at a scale of 1:100,000 were corrected. Within the database,
geologic contacts are represented as lines (arcs), geologic units as
polygons, and site-specific data as points. Polygon, arc, and point
attribute tables (.pat, .aat, and .pat, respectively) uniquely identify
each geologic datum.

Data package contents:
>chew_geo.e00 Contacts, faults, geologic unit labels
>chew_pts.e00 Attitudes and their dip values. Dip values plotted
> as annotation.
>chew_xs.e00 lines of cross sections
>chew_ldr.e00 unit label leaders
>chew_hyps.e00 Topography
>chew_trans.e00 Roads, cultural information
>lines.rel.e00 Line dictionary
>points.rel.e00 Point dictionary
>scamp2.shd.e00 SCAMP shade set