Geologic Map and Digital Database of the Porcupine Wash 7.5 minute Quadrangle, Riverside County, Southern California

INTRODUCTION

The Southern California Areal Mapping Project (SCAMP) has undertaken regional geologic mapping investigations in Joshua Tree National Park, sponsored by Geologic Division's National Cooperative Geologic Mapping Program in cooperation with the National Park Service. These investigations span the east end of Pinto Basin and include parts of the Eagle, Cottonwood, Hexie, and Pinto Mountains. Quadrangles being mapped include the Conejo Well, Porcupine Wash, San Bernardino, and Pinto Mountain 7.5' quadrangles, Riverside County, California. Mapping of the Porcupine Wash quadrangle has been directed toward generating a multipurpose digital geologic map database. The quadrangle, situated in the eastern Transverse Ranges physiographic and structural province, encompasses parts of the northwestern Eagle, northeastern Cottonwood, and southeastern Hexie Mountains and part of the south flank of Pinto Basin. It is underlain by a basement terrane comprising Proterozoic metamorphic rocks, Mesozoic plutonic rocks, and Mesozoic and Mesozoic or Cenozoic hypabyssal dikes. The basement terrane is capped by a widespread Tertiary erosion surface preserved in remnants in the Eagle Mountains and buried beneath Cenozoic deposits in Pinto Basin. In adjacent quadrangles, Miocene basalt overlies the erosion surface. A sequence of at least three Quaternary pediments is planed into the north piedmont of the Eagle Mountains, each in turn overlain by successively younger residual and alluvial deposits. The Tertiary erosion surface is deformed and broken by north-northwest-trending, high-angle, dip-slip faults in the Eagle Mountains and an east-west trending system of high-angle dip- and left-slip faults. In quadrangles around the Porcupine Wash quadrangle, faults of the both sets displace Miocene sedimentary rocks and basalt deposited on the Tertiary erosion surface and Pliocene and (or) Pleistocene deposits that accumulated on the oldest pediment.

This illustration is a .jpg (JPEG) non-navigable image of the USGS geologic-map plot of the Porcupine Wash quadrangle. A full-size, navigable map graphic can be viewed on-screen (pwash_map.pdf ) or can be plotted either from the PostScript file (pwash_map.ps.gz) or the PDF file. Note: the full-size plot requires a large-format plotter, and is best reproduced at 600 (or greater) dpi.

Visit the GeoScience Node of the National Spatial Data Clearinghouse to find other geologic-map datasets in southern California or elsewhere in the Nation

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For questions about the content of this report, contact Robert Powell