RESISTIVITY STRUCTURE ALONG THE SOUTH RIM: PRELIMINARY RESULTS FROM AN AIRBORNE ELECTROMAGNETIC SURVEY OF THE HUALAPAI PLATEAU AND TRUXTON BASIN NEAR GRAND CANYON WEST, ARIZONA, USA

The Grand Canyon region has spectacular outcrop exposure in the modern canyon walls, but limited details on geologic structure are available where the terrain remains undissected. On the western Hualapai Indian Reservation along the south rim, limited water resource development and mineral exploration have resulted in very few wells, leading to structural maps that are well defined near canyons but poorly constrained elsewhere. As part of broader groundwater availability study of the Hualapai Reservation, the U.S. Geological Survey acquired a 1480-km airborne electromagnetic and magnetic survey of the Hualapai Plateau and Truxton Basin in March of 2018. Flight line spacing varies from 1 to 4 km, with a processed along-line resolution of 30-50 m between data points, providing an unprecedented view of the resistivity structure of this region. From these data, high-resolution interpretive maps of the top of the Bright Angel Shale and Precambrian crystalline rocks have been developed. This presentation will highlight these maps, as well as AEM-derived resistivity models that resolve features of geologic interest, such as the subsurface geometry of paleocanyons, volcanic flows, and faults. One such feature includes the southern terminous of the Hurricane fault, an active extensional fault along the margin between the Basin and Range and Colorado Plateau provinces which lies within the Truxton basin survey area.