Geologic Map of the Bachelor Mountain 7.5' Quadrangle, Riverside County, California

This data set maps and describes the geology of the Bachelor
Mountain 7.5' quadrangle, Riverside 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) a coverage containing structural data, (3) a
coverage containing geologic unit annotation and leaders, and
(4) 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), and a key for point
and line symbols, and (2) PDF files of the Readme (including
the metadata file as an appendix), and the graphic produced by
the Postscript plot file.
The Bachelor Mountain quadrangle is located in the southern
Perris block area of the Peninsular Ranges Province.
Internally, the Perris block is a relatively stable area
located between the Elsinore and San Jacinto Fault zones.
In contrast to the rest of the quadrangle, the southern half is
underlain almost entirely by young sedimentary units, chiefly
the Pauba Formation of Pleistocene age. The Pauba Formation
largely consists of well-indurated sandstone containing sparse
cobble-to boulder conglomerate beds. It is eroded into a
gentle badlands topography in most of its extent. Remnants of
scattered, discontinuous alluvial deposits suggest the Pauba
Formation was covered by relatively thin younger Pleistocene
sediments. The most extensive remnant of these younger
deposits forms a surface of low relief at Buck Mesa, just north
of Long Valley.
The northern half of the quadrangle is underlain by Mesozoic
metasedimentary rocks that are intruded by plutonic rocks of
the Cretaceous Peninsular Ranges batholith. The western part
of these metamorphic rocks are mainly phyllite, grading
eastward into quartzitic and schistose rocks. Metamorphic
grade increases eastward also, to biotite, cordierite-biotite,
and sillimanite schist.
The oldest batholithic rocks in the quadrangle are massive
hornblende gabbro including the large body underlying Bachelor
Mountain. Large masses of gabbro are included in granodiorite
and tonalite plutons east of Bachelor Mountain. In the
northwestern part of the quadrangle is the southeastern part of
the Paloma Valley Ring complex. This complex makes up much of
the northern part of the Murrieta quadrangle and the southern
part of the Romoland quadrangle. In the Bachelor Mountain
quadrangle, rocks of the complex are limited to foliated
tonalite which is the most mafic part of the complex. East of
Skinner Reservoir (Lake Skinner) underlying the Tucalota Hills,
is a series of north-trending massive-textured granodiorite
plutons informally termed the granodiorite of Tucalota Hills
(Morton, 1999).
The geologic map data base contains original U.S. Geological
Survey data generated by detailed field observation recorded on
1:24,000 scale aerial photographs. The map was created by
transferring lines from the aerial photographs to a 1:24,000
scale topographic base. The map was digitized and lines,
points, and polygons were subsequently edited 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 are polygons, and
site-specific data as points. Polygon, arc, and point
attribute tables (.pat, .aat, and .pat, respectively) uniquely
identify each geologic datum.