The purpose of this study is to describe the stratigraphy and interpret the environments of deposition in the upper part of the Paleocene Fort Union Formation. Of all the lithofacies present within the study area, sandstone is the most dominant and makes up most of the upper part of the Fort Union Formation along the western edge of the Powder River basin, Wyoming. This sandstone lithofacies occurs in three forms: 1) pink conglomeratic sandstone, 2) coarse-grained sandstone, and 3) fine-grained sandstone. The pink conglomeratic sandstone lithofacies forms a series of Stacked channel bodies in which the clasts are as much as 1 3/4 in. in diameter. The coarse-grained sandstone lithofacies is laterally equivalent to the pink conglomeratic sandstone sequence, but contains smaller clasts; it is arranged en echelon (offset) to the north. The fine-grained sandstone lithofacies, limited to the northern part of the study area, is not as laterally continuous as the pink conglomeratic sandstone lithofacies to the south. Basal lag conglomerate underlies both the conglomeratic sandstone and coarse-grained sandstone lithofacies, but not the fine-grained sandstone. The presence of a fine-grained sandstone lithofacies lateral to the conglomeratic sandstone and coarse-grained sandstone lithofacies suggests the presence of a coarse-grained braided and meandering fluvial system coeval with a fine-grained meandering fluvial system.. The meandering fluvial systems drained the alluvial plain flanking the Bighorn Mountains on the west and the Casper arch on the southwest, and flowed north-northeastward within the Powder River basin.