Geologic map and digital database of the Pinto Mountain 7.5 minute quadrangle, Riverside County, California

This data set maps and describes the geology of the Pinto Mountain 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 northeastern Hexie Mountains,
central Pinto Mountains, and central Pinto Basin.
The quadrangle is underlain by a basement terrane comprising Proterozoic
metamorphic rocks, Mesozoic plutonic rocks, and Mesozoic and Mesozoic and (or)
Cenozoic hypabyssal dikes. The basement terrane is capped by a widespread
Tertiary erosion surface preserved in remnants in the Hexie and Pinto Mountains
and buried beneath Cenozoic deposits in Pinto Basin. Locally, a cover of
Miocene sedimentary deposits and basalt overlie the erosion surface.
Quaternary and (or) Tertiary lacustrine deposits crop out in the center of
Pinto Basin and interfinger laterally with sandstone, conglomerate, and debris
flows originating in the Pinto and Hexie Mountains. A sequence of at least
three Quaternary pediments is planed into the north piedmonts of the Hexie and
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
Pinto Mountain 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 Pinto Mountain 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 eight 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); structural point
data layers showing (4) bedding attitudes, (5) foliation attitudes, (6)
lineations, (7) minor fold axes; and (8) 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.