EVIDENCE FOR A SHORT-LIVED LAKE RISE ~148 KA, LIKELY INDUCED BY FAULT-DAMMING OF THE AMARGOSA RIVER SOON AFTER THE DEMISE AND DRAINING OF LAKE TECOPA (CA)

East of Tecopa Hot Springs 1 to 2.5 km, atop low mesa-like surfaces, are patches of post-Lake Tecopa gravel and sand that appear to be deltaic lake sediments from Chicago Valley drainage. They attain 445m altitude and >3 m thick locally, but thin rapidly to imperceptible. They likely record a short-lived lake rise that interrupted erosional history soon after Lake Tecopa’s ~ 186 ka overflow. Calcareous cement (algal?) in deltaic gravel gave a U-Th age of 148±8 ka. These sediments overlie 1 to several m of cobbly alluvium from Chicago Valley, deposited after overflow of Lake Tecopa, after severe erosion, and late in development of the #1 post-Lake Tecopa alluvial surface. It is unlikely that climatic change caused this sudden lake rise; more likely it was fault-damming of the Amargosa River. I postulate that the damming was by a fault that crosses Armargosa River gorge 6 km (beeline) south of Tecopa general store and 1.2 km above the Willow (China Ranch) Wash junction. The fault strikes NNE and marks an abrupt narrowing of the river gorge, likely because its uplifted west side created a temporary sill. In the wider valley upstream, copious sidewash alluvium remains trapped and river terrace-gravel remnants are preserved. Possible confirmation of this interruption of through drainage from Tecopa Valley into Death Valley is from a core from Badwater: a short-lived desiccation of Lake Manly to a hypersalinity salt pan occurred ~148 ka.