Glaciation in the Great Basin of the Western United States

Forty individually named ranges, plateaus, and massifs draining wholly or partly into the Great Basin of the western United States show definite evidence of Pleistocene glaciation. The most obvious deposits are a family of moraines designated, among other names, "Tioga", "Angel Lake", and "Pinedale". Such moraines generally can be traced from range to range away from described type moraines. These deposits have been numerically assigned to Late Wisconsinan glaciation in the Wasatch Range, White Mountains, Boulder Mountain, and Sierra Nevada on the basis of radiocarbon and surface-exposure ages, and have been assigned to Late Wisconsinan time in several other ranges on the basis of relative-age studies. The type Angel Lake moraine, and most other equivalent moraines across the Great Basin, are thick, hummocky, lobate piles of till rather than looping ridges. The thicknesses of the moraines (often 60 + m) can be explained by heavy debris loads, and/or glacial advance, retreat, and readvance to the same positions a number of times, which is consistent with recent evidence that multiple Late Wisconsinan advances, possibly related to Heinrich and Dansgaard-Oeschger events, occurred in the Sierra Nevada. Pre-Angel Lake deposits occur in many Great Basin ranges, but it is currently difficult or perhaps impossible to determine if these deposits are equivalent to each other and what their relationship is to pre-Tioga deposits in the Sierra Nevada. Numerical ages are rare and relative-a-e studies suggest that pre-Angel Lake deposits may be products of more than one glaciation. Mapped pre-Angel Lake glaciers were longer than their Angel Lake counterparts, but the length differences do not translate into large differences in ELA depression. There is evidence of two minor latest Pleistocene or early Holocene advances in some ranges, judging from the presence of overlying Mazama tephra and/or weathering comparisons to local Angel Lake moraines. In the latter part of the Holocene, ELA's were sufficiently high that only the highest, wettest ranges developed Neoglacial glaciers. There does not appear to be a consistent pattern of latest Pleistocene/Holocene glacial fluctuations along an east-west transect through the Cordillera, or even through the Great Basin. (C) 2001 Elsevier Science Ltd. All rights reserved.