The subhorizontal and essentially undeformed late Pliocene and Holocene Tecopa Lake beds (below) contain several volcanic ash beds. The youngest ash, within a few meters of the top of the lake beds, yields a tephrachronology age of 160,000 years (Morrison, 1991). The youngest lake beds crop out at an elevation of 550 m; the Amargosa River has dissected the lake beds to an elevation of 403 m near the southern end of this ancient lake. These data define an average erosion rate of 0.9 mm/yr for the Tecopa Lake Beds during the last 160,000 years.