The Las Vegas Valley Shear Zone, a right lateral strike slip fault that trends >100 m at N60W, makes a right step east of Beatty, Nevada resulting in detachment faulting and rhyolitic volcanism characteristic of the South West Nevada Volcanic Field. In the Fluorspar Canyon region of the field area, the Fluorspar Canyon-Bullfrog Hills (FC-BH) detachment dips 40° N and separates Late-proterozoic and Paleozoic strata in the footwall from Tertiary Volcanics and sediments in the hanging wall. To the east, the detachment links with the moderately dipping Tate's Wash Fault. After removing the 40°N tilt, these two structures form a listric normal fault that cuts through the Paleozoic and into the crystalline basement. The hanging wall does not crop out in the field area and may be represented by the strata of the Grapevine Mountains of Death Valley. Extension along the FC-BH detachment migrates westward and occurs in previously recognized pulses. Expansive breccias are a distinctive feature in the field area and are directly related to extension. This study examines mapped breccias to determine their origin and relationship to deep structures in the field area. Deposits related to deep structures may influence the flow of possibly contaminated groundwater from Pahute Mesa in the Nevada Test Site southwest into the Beatty region. Breccias are interpreted to be deposited as large slide masses or accumulated in extension-related low areas. Groundwater flows southwest possibly using the NE trending Thirsty Canyon Lineament as a pathway. Water ponds against the east side of the N- trending Hogback Fault as suggested by the presence of numerous springs. The breccias mapped in the study area are not directly fault related, do not cut the underlying detachment, and do not significantly influence groundwater flow. Flow continues southward into the Beatty, Nevada region via the Amargosa River
