Geophysics Field Camp 1999

A geophysical study of the Patagonia-Sonoita Nature Conservancy property was carried out to determine the depth to bedrock and the geometry of the underlying basin in the area. The survey was part of the ongoing U.S. Geological Survey studies of the region. CSAMT, TEM, DC Resistivity, Seismic, Gravity, and Magnetic surveys were performed. Many of the surveys were not able to map depth to bedrock because the depth of penetration of these surveys was less than the large depth to bedrock, which we encountered in this area. The best estimate of depth to bedrock in the center of the valley is of the order of one kilometer, as identified by the CSAMT surveys. The CSAMT survey found a significant low-resistivity anomaly in the vicinity of the Nature Conservancy Visitor Center. This low-resistivity anomaly could be due to clay-rich rocks or possibly mineralized rocks. Magnetic and TEM anomalies also occurred in the same area as the CSAMT low-resistivity anomaly. Seismic surveys showed a loosely consolidated surface layer above more consolidated alluvium. The model from the · Gravity survey shows an extensive alluvial basin overlying rhyolite with high and low-angle faults.The Geophysics Field Camp Reports are made available by the Laboratory for Advanced Subsurface Imaging (LASI) and the University of Arizona Libraries. Visit the LASI website for more information http://www.lasi.arizona.edu