T108 Geologic Maps, Digital Geologic Maps, and Derivatives from Geologic and Geophysical Maps (Posters)

Monday, 1 November 2010
8:00 AM - 6:00 PM
Hall D

DIGITAL GEOLOGIC MAP OF THE PICACHO, PICACHO NW, PICACHO SW, AND HIDDEN VALLEY 7.5' QUADRANGLES, ARIZONA AND CALIFORNIA

Paper number: T108-47
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

We present a digital geologic map of the Picacho, Picacho NW, Picacho SW, and Hidden Valley 7.5’ Quadrangles, Arizona and California, based on field work conducted during the 1970s-1980s by three of the authors (Sherrod, Tosdal, and Haxel). Geologic features were recorded in the field on aerial photographs and transferred in the office to a 1:50,000 scale mylar master of the four joined topographic base maps. An initial digital version in ArcINFO was prepared by Tian (1999). Contacts were traced on a digitizing tablet, with each quadrangle georeferenced separately to avoid misfits at the quadrangle boundaries. This version has now been updated in ArcGIS. Linework was checked against a georeferenced scanned image of the mylar and edited as necessary. A digital raster image of the topographic base was incorporated from the Cal-Atlas Geospatial Clearinghouse. Rectification and mosaic tools were utilized to produce the best fit between the vector (contacts, faults) and raster (topographic base) data. Structural attitudes of planar and linear features were added from the mylar. The color scheme for geological units was coordinated with that for published maps for the surrounding region.

The map reveals two major low-angle fault systems, the Chocolate Mountains fault (CMF) and the Gatuna-Sortan fault (GSF). The CMF was active in the early Cenozoic and accommodated exhumation of a Late Cretaceous-early Cenozoic subduction complex in the footwall (Orocopia Schist). The structurally higher GSF separates a footwall of lower- to middle-crustal Mesozoic(?) gneiss from a hanging wall of relatively shallow Jurassic plutonic rocks and Jurassic-Cretaceous low-grade metavolcanic and metasedimentary rocks. The GSF was active during late Oligocene-early Miocene regional extension. It may also have undergone an earlier phase of movement related to slip on the CMF. Early Miocene volcanic rocks are in fault contact with the Orocopia Schist and in fault and depositional contact with the plutonic and metamorphic rocks above the CMF and GSF. Geologic relations in the map region are representative of those along a 100 km east-west transect from southeasternmost California into southwesternmost Arizona.