Geologic Map of the San Bernardino North 7.5' Quadrangle, San Bernardino County, California, USGS OFR 01-131

The data set for the San Bernardino North 7.5' quadrangle was prepared under
the U.S. Geological Survey Southern California Areal Mapping Project (SCAMP) a
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 San Bernardino North 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,
itcan be used for groundwater studies in the San Bernardino basin, and 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 San Bernardino North 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 Description of 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 the graphic produced by the PostScript plot file.

The geologic map covers a part of the southwestern San Bernardino Mountains and
the northwestern San Bernardino basin. Granitic and metamorphic rocks underlie
most of the mountain area, and a complex array of Quaternary deposits fill the
basin. These two areas are separated by strands of the seismically active San
Andreas Fault. Bedrock units in the San Bernardino Mountains are dominate by
large Cretaceous and Jurassic granitic bodies, ranging in composition from
onzogranite to monzodiorite, and include lesser Triassic monzonite. The younger
of these granitic rocks intrude a complex assemblage of gneiss, marble, and
granitic rock of probable early Mesozoic age; the relationship between these
metemorphic rocks and the Triassic rocks is unknown. Spanning the Pleistocene
in age, large and small alluvial bodies emerge from the San Bernardino
Mountains, and and fill the San Bernardino basin. In the southwestern part of
the quadrangle, Cajon Wash carries sediments from both the San Bernardino and
San Gabriel Mountains, and Lytle Creek heads in the eastern San Gabriel
Mountains. Limite bedrock areas showing through the Quaternary sediments of the
basin consist exclusively of Mesozoic Pelona Schist locally intruded by
Tertairy dikes. Youthful-appearing fault scarps discontinuously mark the
traces of the San Andreas Fault along the southern edge of the San Bernardino
Mountains. Unnamed Tertiary sedimentary rocks are bounded by two strands of
the fault between Badger Canyon and the east edge of the quadrangle. Young and
old high-angle faults cut bedrock units within the San Bernardino Mountains,
and the buried, seismically active San Jacinto Fault traverses the southwestern
part of the quadrangle.

The geologic map database contains original U.S. Geological Survey data
generated by detailed field observation and by interpretation of aerial
photographs. This digital Open-File map superceeds an older analog Open-File
map of the quadrangle, and includes extensive new data on the Quaternary
deposits, and revises some fault and bedrock distribution within the San
Bernardino Mountains. The digital map was compiled on a base-stable cronoflex
copy of the San Bernardino North 7.5' topographic base and then scribed. This
scribe guide was used to make a 0.007 mil blackline clear-film, which was
scanned at 1200 DPI by Optronics Specialty Company, Northridge, California;
minor hand-digitized additions were made at the USGS. Lines, points, and
polygonswere subsequently edited at the USGS using standard ARC/INFO commands.
Digitizing and editing artifacts significant 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.