The Wono and Trego Hot Springs (THS) tephras are widespread in the Lahontan basin and have been identified in a variety of sedimentary environments at different elevations. Davis (1983) reported lake level to be at about 1256 m when the THS tephra was deposited, an interpretation questioned by Benson et al. (1997) who interpreted lake level to be ≤1177 m at that time. This is a significant difference in lake size with important implications for interpreting the climate that prevailed at that time. Based on new interpretations of depositional settings of the THS bed at multiple sites, the larger lake size is correct. Additional sites containing the Wono tephra indicate that it was deposited when lake level was at about 1217 m in the western subbasins and at about 1205 m in the Carson Sink. Sedimentary features associated with progressively deeper paleowater depths follow a predictable pattern that is modulated by proximity to sediment sources and local slope. Fine to coarse sands with wave-formed features are commonly associated with relatively shallow water. Silty clay or clay dominates in paleowater depths >25 m, with thin laminae of sand and ostracods at sites located adjacent to or downslope from steep mountain fronts.

Tephra layers form important chronostratigraphic marker horizons within the Wisconsinan loess-paleosol stratigraphy of the Palouse, Washington State. This paper details the presence of disseminated glass shards of the Trego Hot Springs tephra that has not previously been recognized within the Palouse or environs. The tephra provides additional chronological control for the regional Late Wisconsinan stratigraphy and raises the possibility of correlating the paleoclimatic proxy record contained within the Palouse to those of lake sequences in Oregon, California, and Nevada.