The paleoclimatic history of western Utah is being investigated as part of the USGS Global Change and Climate History Program studies of long-term climatic changes in the western United States. The initial objective of the study is to document the environmental conditions during the mid-Pliocene period of warmer-than-modern global climates (the focus of the USGS Pliocene Research, Interpretation, and Synoptic Mapping [PRISM] project). The investigation also seeks to determine how and when these conditions gave way to the late Quaternary pattern of climatic variations (in which short periods of very moist climates have been separated by long periods of arid conditions). This is a collaborative project involving specialists from the USGS, Kansas State University, and the University of California-Davis in paleontology (Thompson, Buchner, Forester, Bradbury), stratigraphy and sedimentology (Oviatt, Kelsey, Bracht), and paleomagnetism and environmental magnetism (Roberts). The data presented herein represent preliminary findings of the analyses of two cores of Pliocene and early Pleistocene sediments from the eastern Great Basin.