RESOLVING DIFFERENCES IN MODELS FOR THE DEMISE OF PLEISTOCENE LAKE TECOPA, SOUTHEASTERN CALIFORNIA

Reheis et al. (2019) and Larsen and Olson (2019) proposed different models for the lake-level history of Pleistocene Lake Tecopa, a significant terrestrial paleoclimate record in the western US. Recent field observations, especially along the southern margin of the basin, clarify the latter lake phases in the basin. A critical difference in the two models is that Larsen and Olson (2019) invoke uplift at the southern margin of the basin to contain higher lake levels during the Middle Pleistocene. Exposures along the north side of the Sperry Hills (aka Tecopa Hump) reveal shoreline deposits for the highest lake level at ~535 m, compared to similar high lake shorelines at ~520 m within the central part of the Tecopa basin. These observations suggest as much as ~15 m of post-depositional uplift along the southern margin of the basin during the late middle Pleistocene. Larsen and Olson (2019) interpret the high lake (their HL2) to have overflowed the Tecopa Hump and initiated the incision history of a through-flowing Amargosa River at approximately 300 ka, whereas Reheis et al (2019) place this lake phase at 580 ka. Reheis et al. (2019) interpret the final lake, their Terminal Lake, at 185 ka to have reached an elevation of 505 m. Shoreline deposits of this lake are extensively exposed in the northern part of the basin at 505 to 510 m, where they are inset into older Lake Tecopa beds. Along Willow Creek Wash on the Tecopa Hump, fan-delta deposits are inset into the canyon to elevations of ~ 510 m. These observations clarify that the Terminal Lake formed following significant incision, either during or shortly after the final phases of uplift along the Tecopa Hump. Another lake phase, estimated at 150 ka, is also represented by fan-delta deposits in the canyon and correlative shoreline deposits within the basin at ~440 m. A prominent fluvial terrace graded to the 440-m base level is also present along the Amargosa River. Holocene lake phases are represented by fine-grained deposits and correlative fan-delta deposits in Amargosa Canyon. The recent field observations support aspects of both proposed models and place the history of Lake Tecopa into the context of the deformation of the Tecopa Hump and incision of the Amargosa River.