Two additions are proposed to Black-welder's classical sequence of four Pleistocene glaciations (Tioga, Tahoe, Sherwin, and McGee) of the Sierra Nevada. The younger, the Tenaya, lies between Tioga and Tahoe, giving a three-fold subdivision of the Wisconsin. The older, named Mono Basin, fills the long-recognized gap between Tahoe and Sherwin; it is possibly Illinoian. Evidence for the Mono Basin glaciation is scanty because its ice streams were less extensive than the subsequent Tahoe glaciers.

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