Geologic Map of the Fifteenmile Valley 7.5' Quadrangle, San Bernardino County, California, USGS OFR 00-132

The data set for the Fifteenmile Valley 7.5' quadrangle was prepared under the
U.S. Geological Survey Southern California Areal Mapping Project (SCAMP) as
part of an ongoing effort to develop a regional geologic framework of southern
California, and 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 Database of the
National Cooperative Geologic Mapping Program of the USGS.

The digital geologic map database for the Fifteenmile Valley 7.5' 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 San Bernardino National Forest. The
database is not suitable for site-specific geologic evaluations.

This data set maps and describes the geology of the Fifteenmile Valley 7.5'
quadrangle, San Bernardino County, California. 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)
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, a Correlation of Map Units (CMU)
diagram, a Descriptionof Map Units (DMU), an index map, a regional geologic and
structure map, and a key for point and line symbols; (2) PDF files of this
Readme (including the metadata file as an appendix), Description of Map Units
(DMU), and a screen graphic of the plot produced by the PostScript plot file.

The geologic map covers the northernmost part of the San Bernardino Mountain
and the southern Granite Mountains. These two bedrock areas are separated by
the wide, alluviated Fifteenmile Valley. Bedrock units in the San Bernardino
Mountains are dominated by large Cretaceous granitic bodies ranging in
composition from monzogranite to gabbro, and include lesser Triassic monzonite.
The Granite Mountains are underlain chiefly by large Triassic monzonite
bodies, and in the western part, by Cretaceous and possibly Jurassic
monzogranite to monzodiorite. Spanning the Pleistocene in age, large alluvial
fans, flank the north side of the San Bernardino Mountains, and are dominated
by debris flow deposits. The central part of Fifteenmile Valley is covered by
fine grained alluvial material deposited by streams flowing into Rabbit Lake
and an unnamed dry lake in the northwestern part of the quadrangle. Young,
south dipping reverse faults, some with moderately to well eroded fault scarps,
discontinuously flank the northern edge of the San Bernardino Mountains. Young
and old high-angle faults are mapped within both the San Bernardino and Granite
Mountains.

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 on a base-stable cronoflex copy of the
Fifteenmile Valley 7.5' topographic base and then scribed. This scribe guide
was used to make a0.007 mil blackline clear-film, which was scanned at 1200 DPI
by Optronics Specialty Company, Northridge, California; minor hand-digitized
additions were madeat the USGS. Lines, points, and polygons were subsequently
edited at the USGS using standard ARC/INFO commands. Digitizing and editing
artifacts significan enough to display at a scale of 1:24,000 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.