Soil-Geomorphic Analysis of Late-Pleistocene Glacial Sequences in the McGee, Pine, and Bishop Creek Drainages, East-Central Sierra Nevada, California

Abstract

Late-Pleistocene glacial sequences at McGee, Pine, and Bishop creeks, in the east-central Sierra Nevada, are resolvable into distinct relative-age groups on the basis of soil development, the weathering of surface and subsurface clasts, and geomorphic criteria. The data differentiate moraines from Tioga and Tahoe glaciations at McGee Creek, and Tioga, Tahoe, and pre-Tahoe/post-Sherwin glaciations at Pine and Bishop creeks; no moraines from a Tenaya glaciation are differentiated by the data, perhaps because the soil-geomorphic methods are not sensitive enough to resolve small age differences between moraines. The lack of fine age resolution is probably due to a combination of factors, including (1) slow rates of soil development, (2) low amounts of atmospheric dust added to the soils, (3) the susceptibility of crest soils to erosion, and (4) the susceptibility of footslope soils to burial by colluvium. Age resolution is improved by evaluating soils at both the moraine crests and the relatively wetter footslope sites, and by basing age assignments on a combination of macro- and micromorphologic soil properties, the disintegration of subsurface clasts, and parameters of surface-clast weathering.