Geologic map and digital database of the San Bernardino Wash 7.5 minute quadrangle, Riverside County, California

This data set maps and describes the geology of the San Bernardino Wash 7.5 minute
quadrangle, Riverside County, southern California. The quadrangle, situated in
Joshua Tree National Park in the eastern Transverse Ranges physiographic and
structural province, encompasses parts of the northwestern Eagle Mountains,
east-central Pinto Basin, and eastern Pinto Mountains.
The quadrangle is underlain by a basement terrane comprising metamorphosed
Proterozoic strata, Mesozoic plutonic rocks, and Jurassic and Mesozoic and (or)
Cenozoic hypabyssal dikes. The basement terrane is capped by a widespread Tertiary
erosion surface preserved in remnants in the Pinto and Eagle Mountains and buried
beneath Cenozoic deposits in Pinto Basin. Locally, a cover of Miocene sedimentary
deposits and basalt overlie the erosion surface. A sequence of at least three
Quaternary pediments is planed into the north piedmont of the Eagle Mountains, each
in turn overlain by successively younger residual and alluvial, surficial deposits.
The Tertiary erosion surface is deformed and broken by north-northwest-trending,
high-angle, dip-slip faults in the Pinto and Eagle Mountains and an east-west
trending system of high-angle dip- and left-slip faults along the range fronts
facing Pinto Basin. In and around the San Bernardino Wash quadrangle, faults of
the north-northwest-trending set displace Miocene sedimentary rocks and basalt
deposited on the Tertiary erosion surface and some of the faults may offset
Pliocene and (or) Pleistocene deposits that accumulated on the oldest pediment.
Faults of this system appear to be overlain by Pleistocene deposits that
accumulated on younger pediments. East-west trending faults are younger than and
perhaps in part coeval with faults of the northwest-trending set.
The San Bernardino Wash database was created using ARCVIEW and ARC/INFO, which are
geographical information system (GIS) software products of Envronmental Systems
Research Institute (ESRI). The database comprises five coverages: (1) a geologic
layer showing the distribution of geologic contacts and units; (2) a structural
layer showing the distribution of faults (arcs) and fault ornamentation data
(points); (3) a layer showing the distribution of dikes (arcs); a structural point
data layer showing (4) bedding and metamorphic foliation attitudes, and (5)
cartographic map elements, including unit label leaders and geologic unit
annotation. The dataset also includes a scanned topographic base at a scale of
1:24,000. Within the database coverages, geologic contacts , faults, and dikes are
represented as lines (arcs and routes), geologic units as areas (polygons and
regions), and site-specific data as points. Polygon, region, arc, route, and point
attribute tables uniquely identify each geologic datum and link it to descriptive
tables that provide more detailed geologic information.
The digital database is accompanied by two derivative maps: (1) A portable document
file (.pdf) containing a navigable graphic of the geologic map on a 1:24,000
topographic base and (2) a PostScript graphic-file containing the geologic map on a
1:24,000 topographic base. Each of these map products is accompanied by a marginal
explanation consisting of a Description of Map Units (DMU), a Correlation of Map
Units (CMU), and a key to point and line symbols. The database is further
accompanied by three document files: (1) a readme that lists the contents of the
database and describes how to access it, (2) a pamphlet file that describes the
geology of the quadrangle and (3) this metadata file.