Bedrock Geology of the Turkey Creek Drainage Basin

This data set was created for analysis of the ground-water system of the study
area.

This geospatial data set describes bedrock geology of the Turkey Creek drainage
basin in Jefferson County, Colorado. It was digitized from maps of fault
locations and geologic map units based on age and lithology. Created for use in
the Jefferson County Mountain Ground-Water Resources Study, it is to be used at
a scale no more detailed than 1:50,000.

The source materials for the generation of this data set consist of bedrock
geology mapped on U.S. Geological Survey (USGS) topographic quadrangles at a
scale of 1:24,000 by the USGS. The source materials were converted to digital
format, topologically developed, and attributed on a quadrangle-by- quadrangle
basis before being combined into one data set.

The procedures for converting the materials to digital format differed for each
quadrangle and are summarized as follows:

Conifer

The original camara-ready transparency of the map publication, Reconnaissance
Geologic Map of the Conifer Quadrangle, Jefferson County, Colorado, was
obtained from the USGS. A film-positive was made from this transparency. To
simplify the linework, this film-positive was then traced by hand onto mylar.
The mylar was then digitally scanned at 300 dots per inch (dpi) and stored as a
TIFF image. Using Arc/INFO software from Environmental Systems Research
Institute, the image was georeferenced to real-world coordinates and converted
into an Arc/INFO raster data set format known as a grid, which was then
vectorized into an Arc/INFO vector data set format known as a coverage. A
quadrangle boundary outline that was generated from quadrangle boundary
coordinates and then projected into real-world coordinates was added to the
coverage, which was then converted to a coverage with polygon topology. Line
features in the coverage were attributed according to fault type
classification, and the polygon features were attributed according to bedrock
geologic map unit and fault zone classification.

Evergreen

An incomplete collection of the original pre-press mylar separates for the map
publication, Geologic Map of the Evergreen Quadrangle, Jefferson County,
Colorado, was obtained from the USGS. Mylar separates of Quaternary geologic
contacts and faults were identified and digitally scanned at 300 dpi into TIFF
images. All other geologic contacts in the area of interest were traced onto
mylar from a paper print of the map publication. Furthermore, an enclosing
polygon outline outside of the area of interest was drawn on the mylar so that
the traced contacts would form polygon features. The mylar was then digitally
scanned at 300 dpi into a TIFF image. All the images were then georeferenced to
real-world coordinates, converted into grids, and vectorized into three
separate coverages, one for each of the two mylar sources, and one for the
traced source. These coverages were then combined into one coverage. One of the
authors of the map publication provided updated nomenclature for Precambrian
map units (Bruce Bryant, U.S. Geological Survey, oral communication, 1998) so
that the nomenclature would match that of adjacent quadrangles. The line
features in the coverage were attributed according to fault type, and polygon
features were attributed according to geologic map unit and fault zone
classification.

Indian Hills

A paper print of the map publication, Geologic Map of the Indian Hills
Quadrangle, Jefferson County, Colorado, was obtained from the USGS. For the
area of interest on the quadrangle, two mylars were hand-traced from this paper
print. One mylar consisted of geologic contacts and an enclosing polygon
outline outside of the area of interest that was drawn so that the contacts
would form polygon features. The other mylar consisted of fault traces. The two
mylars were then digitally scanned at 300 dpi into TIFF images. These images
were georeferenced to real-world coordinates and converted into grids which
were then vectorized into coverages. The coverages were then combined into one
coverage. One of the authors of the map publication provided updated nomencla-
ture for Precambrian map units (Bruce Bryant, U.S. Geological Survey, oral
communication, 1998) so that the nomenclature would match that of adjacent
quadrangles. Line features in the coverage were attributed according to fault
type, and polygon features were attributed according to geologic map unit and
fault zone classification.

Meridian Hill

A paper photocopy of preliminary geologic mapping consisting of faults and
geologic contacts for the Meridian Hill Quadrangle, Clear Creek, Jefferson, and
Park Counties, was obtained from the USGS. For the area of interest on this
quadrangle, all the linework was traced onto mylar. Furthermore, an enclosing
polygon outline outside of the area of interest was drawn on the mylar so that
the traced contacts would form polygon features. The mylar was then digitally
scanned at 300 dpi into a TIFF image. The image was georeferenced to real-world
coordinates and converted into a grid which was then vectorized into a
coverage. Line features in the coverage were then attributed according to fault
type, and the polygon features were attributed according to geologic map unit
and fault zone classification.

Morrison

The original pre-press mylar separates for the map publication Geologic Map of
the Morrison Quadrangle, Jefferson County, Colorado, were obtained from the
USGS. The mylar separate of geologic contacts was digitally scanned at 300 dpi
into a TIFF image. This image was georeferenced to real-world coordinates and
converted into a grid which was then vectorized into a coverage. The fault
linework was digitized into a coverage from another mylar separate of the same
publication that had too many other themes on it and was therefore too
difficult to scan and vectorize. The fault coverage was then transformed to
real-world coordinates. The coverages were then combined into one coverage. An
enclosing polygon outline outside of the area of interest was digitized into
the coverage so that the geologic contacts would form polygon features. Line
features in the coverage were attributed according to fault type, and polygons
were attributed according to geologic map unit and fault zone classification.

Once the polygon and vector topology was developed for each quadrangle, the
individual coverages were combined into one coverage. No edgematching was
performed. A study-area outline of the Turkey Creek Watershed was delineated in
Arc/INFO with USGS Digital Elevation Model data sets. A 500-meter buffer
polygon of this outline was used to clip the geology coverage.

Any use of trade, product, or firm names is for descriptive purposes only and
does not imply endorsement by the U.S. Government.