Four major glaciations are recognized in the area studied. Two are pre-Wisconsin in age and named from oldest to youngest, Hobart and Donner Lake. Difficulties in the correlation of the pre-Wisconsin units with Blackwelder's (1931) type localities led to the introduction of a separate pre-Wisconsin chronology. The two Wisconsin glaciations are correlated with the Tahoe and Tioga glaciations of Blackwelder. The Hobart glaciation followed the Plio-Pleistocene deformation of the Sierra Nevada and subsequent erosion of the valleys to about their present level. Glaciers at this time appear to have been quite extensive. Hobart Till is highly weathered, as shown by depth of oxidation, high clay content, disintegrated granitic boulders, and weathering rinds on volcanic boulders. Soils and the amount of subsequent erosion indicate that the Hobart-Donner Lake interglacial was probably the longest of the interglacials. Dormer Lake glaciers were apparently as extensive as, if not more than, the Hobart, with tributary glaciers joining to form a compound valley glacier which occupied the Upper Truckee Canyon and brought about a rise in the level of Lake Tahoe of approximately 600 feet. The till is recognized by a 4- to 8-foot soil with a distinct A-B-C profile in which boulders are weathered to about the same degree as they are in Hobart Till. A relatively long interglacial separates the Donner Lake glaciation from the Tahoe. Tahoe glaciers were much shorter than those of Donner Lake age; glaciers occupied all tributary valleys and some flowed a short distance down the Upper Truckee Canyon, causing a rise of Lake Tahoe of about 90 feet. Till of this age is characterized by its subdued morainal topography, an A-C soil profile, and spheroidally weathered granitic boulders along with fresh volcanic boulders within the zone of weathering. An interglacial period of relatively short duration separates the Tahoe glaciation from the Tioga. Tioga glaciers were slightly shorter, and possibly thinner, than those of Tahoe age. Till of this advance has well-preserved moraine morphology, the soil bears an A-C profile, and boulders within the soil are fresh. Tioga deglaciation was marked by several standstills and followed shortly by a slight readvance from the cirques, here named the Frog Lake advance. Glaciers disappeared during the Hypsithermal. This was followed by a slightly cooler period during which a protalus rampart formed on one of the higher cirque headwalls. A study of glacial outwash deposits shows that stream aggradation accompanied the glacial advances while degradation took place during the interglacials. This is taken to mean that the ice virtually disappeared or retreated far upvalley during interglacial times.