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.