Geologic map of the Fifteenmile Valley 7.5' quadrangle, San Bernardino County, California

Abstract

This data set maps and describes the geology of the Fifteenmile Valley 7.5' quadrangle, San Bernardino 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) 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), an index map, a regional geologic and structure map, and a key for point and line symbols; (2) PDF files of this Readme (including the metadata file as an appendix), Description of Map Units (DMU), and a screen graphic of the plot produced by the PostScript plot file. The geologic map covers the northernmost part of the San Bernardino Mountains and the southern Granite Mountains. These two bedrock areas are separated by the wide, alluviated Fifteenmile Valley. Bedrock units in the San Bernardino Mountains are dominated by large Cretaceous granitic bodies ranging in composition from monzogranite to gabbro, and include lesser Triassic monzonite. The Granite Mountains are underlain chiefly by large Triassic monzonite bodies, and in the western part, by Cretaceous and possibly Jurassic monzogranite to monzodiorite. Spanning the Pleistocene in age, large alluvial fans, flank the north side of the San Bernardino Mountains, and are dominated by debris flow deposits. The central part of Fifteenmile Valley is covered by fine grained alluvial material deposited by streams flowing into Rabbit Lake and an unnamed dry lake in the northwestern part of the quadrangle. Young, south dipping reverse faults, some with moderately to well eroded fault scarps, discontinuously flank the northern edge of the San Bernardino Mountains. Young and old high-angle faults are mapped within both the San Bernardino and Granite Mountains. The geologic map database contains original U.S. Geological Survey data generated by detailed field observation and by interpretation of aerial photographs. The map was compiled on a base-stable cronoflex copy of the Fifteenmile Valley 7.5' topographic base and then scribed. This scribe guide was used to make a 0.007 mil blackline clear-film, which was scanned at 1200 DPI by Optronics Specialty Company, Northridge, California; minor hand-digitized additions were made at the USGS. Lines, points, and polygons were subsequently edited at the USGS 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 as polygons, and site-specific data as points. Polygon, arc, and point attribute tables (.pat, .aat, and .pat, respectively) uniquely identify each geologic datum.