Named Shoshone Springs Alloformation and assigned, along with (ascending) Spanish Trail, Greenwater Fan, and Amargosa Alloformations (all new), to late Miocene to late Pleistocene Lake Tecopa Allogroup (new). Name origin not stated. Found in vicinity of intermittent Amargosa River and towns of Shoshone and Tecopa, ancient Lake Tecopa area, eastern Mojave Desert, Inyo Co., east-central CA. Exposed in intermediate piedmonts of Tecopa basin. Consists of shallow-lake sand (no known gravel), silt, and clay, with tongue of loessial and colluvial sandy silt and paleosols at least as low as 430 m altitude, plus early Pleistocene (738 ka) Bishop tephra layer at base. Thickness is roughly 10 m [inferred]. Discontinuously underlies late Pleistocene (620 ka) Lava Creek B tephra layer (of Amargosa Alloformation). Discontinuously overlies late Pliocene and early Pleistocene Greenwater Fan Alloformation. Age is early and late Pleistocene based on well-dated tephra layers (Sarna-Wojcicki and others, 1987; and Chapter 6 in this volume; Sarna-Wojcicki, personal communication, 1990).

Source: GNU records (USGS DDS-6; Menlo GNULEX).