HYDROGEOLOGIC FRAMEWORK OF THE SOUTHERN DEATH VALLEY FLOW SYSTEM, CALIFORNIA AND NEVADA
Based on new fieldwork, the interbasin flow pathway from Pahrump basin is formed by Paleozoic carbonate rocks that are folded into a broad footwall syncline beneath the Chicago Pass thrust. This geologic feature extends southwestward from Pahrump basin, under two ranges and one intervening basin, and across the Tecopa basin to its southern margin, where it is truncated by the Sheephead fault. The numerous strands of this fault control the locations of the major springs. The chemistry of the Tecopa basin springs indicates a Paleozoic carbonate aquifer source, but also reflects interaction with Proterozoic siliciclastic rocks, increasing to the south. The high temperatures (≤48°C/118°F) of the springs indicate that the carbonates lie at a depth of ≥1-to-3 km under most of Tecopa basin. To reach the surface, the spring water must rise through ≥1-to-3 km of brecciated siliciclastic rocks along fault zones that cut the upper plate of the Chicago Pass thrust.
Based on this framework, the only significant threat to flow in the southern part of Amargosa River is from groundwater overdrafting in Pahrump Valley. This threat can be monitored by the drilling of a 100-170-m well where the footwall syncline intersects the southwest margin of Pahrump basin. Moreover, the flow regime in this groundwater system could be better understood if O- and H-isotopic ratios were determined for all of the major springs.