Bassanite, calcium sulfate hemihydrate, has been identified in drill cores from two desert lake basins, about 175 miles apart, in southeastern California. This finding is significant because the only other reported natural occurrences of bassanite known to the writers are at Mt. Vesuvius, Italy, and in the central Asiatic desert. Palache, Berman and Frondel (1951) describe the Mt. Vesuvius occurrence as follows: “Found in cavities of leucite-tephrite blocks thrown out during the April, 1906, eruption of Vesuvius. Also found with gibbsite in fumaroles of the eruption of 1911.” Middle Asiatic bassanite deposits (Popov and Vorob'ev, 1947) are found in the desert soils of eastern Turkmenia and northern and western Fergana. The mineral occurs as a white powder, a weathering product sometimes pseudomorphic after gypsum. In southern Fergana the hemihydrate occurs as thin layers in oil-bearing sands.