Geologic map of the Sunnymead 7.5' quadrangle, Riverside County, California

Abstract

This data set maps and describes the geology of the Sunnymead 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 Sunnymead quadrangle is located in the northern part of the Peninsular Ranges Province and is underlain by Cretaceous and older basement rocks. This part of the Peninsular Ranges Province is divided into the Perris block, located west of the San Jacinto fault and the San Jacinto Mountains block to the east. The northwest quarter of the quadrangle is crossed diagonally by the San Jacinto fault zone, an important active major fault of the San Andreas fault system. The San Jacinto fault zone consist of a main trace and multiple discontinuous breaks. The main trace forms a dissected, west-facing fault scarp about 1,000 feet above the valley floor. A vaguely located fault in granitic rocks parallel to and west of the San Jacinto fault zone does not appear to cut Pleistocene age alluvial deposits. On the northern side of the San Jacinto fault zone is a thick section of Pliocene and Pleistocene continental sedimentary rocks, the upper part of the San Timoteo beds of Frick(1921). The area underlain by these rocks is termed the San Timoteo Badlands. Most of these beds consist of coarse-grained sandstone, conglomeratic sandstone, and conglomerate. All the clasts within these beds were derived from Transverse Ranges basement rocks that are located to the north of the quadrangle. The San Timoteo beds have been deformed into a broad anticlinal structure produced by the sedimentary beds being compressed as they are translated around a restraining bend in the San Jacinto fault north of the El Casco quadrangle. A curving, diachronous fault produced by this compression is located in the western part of the badlands just east of the San Jacinto fault zone. The area west of the San Jacinto fault zone is underlain by plutonic rocks of the Cretaceous-age Peninsular Ranges batholith with a few small included pendants of schist and gneiss of probable Paleozoic age. Most of the plutonic rocks are of tonalite composition and are mainly biotite-hornblende tonalite. In the northwestern part of the quadrangle is the eastern part of the Box Springs granitic complex, a basinal-shaped complex that appears to be the distal part of a diapiric-shaped complex. Most of the alluviated area west of the San Jacinto fault zone consists of Pleistocene age fluvial deposits. Most of these deposits have a degraded upper surface. The upper surface of these deposits are preserved in some places near the contact with granitic rocks. The upper part of these deposits form the Paloma surface of Woodford and others(1971). Holocene age alluvial fans emanate from the San Timoteo Badlands. 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.