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Other sedimentary formations in the basin include: Wasatch and Green River Formations which consist of loosely cemented, interbedded sandstones, siltstones and mudstones; the Washakie Formation, an interbedded sandstone, siltstone, mudstone and conglomerate; and the Bridger Formation, with shale, mudstone, claystone, siltstone and sandstone. All these formations are relatively young and very erodible in the far western part of the basin where the Paleozoic sedimentary rocks, primarily limestone, sandstone and siltstone are exposed on the surface. Shales are more common in the Cretaceous formations and mudstones are more common in the Tertiary units. These formations are widely exposed due to sparse vegetation and are relatively erodible resulting in high sediment yield from the tributaries. The four major tributaries in the lower Little Snake Basin include: Muddy Creek, Sand Creek, Powder Wash and Sand Wash (Figure 1). The geology of these tributaries are described by Gregory (Rei 1991). Of these four streams, Sand Wash and Muddy Creek are the most prodigious producers of sediment. Muddy Creek drains the Green River and Wasatch Formations and the Sand Wash basin is underlain almost entirely by the Bridger Formation. Sand Creek delivers sediments primarily from the Washakie Formation, the youngest formation (Eocene Epoch) in the Little Snake Basin. Powder Wash drains the Wasatch and Green River Formations. Many of the small streams in these formations are incised. Muddy Creek provides relatively fine sediments while Sand Wash contains high concentrations of sand-sized sediments. There are no quantitative estimates of sediment yield from these tributary systems. River-basin geology also effects channel morphology, river valley slope, sediment contribution and river substrate at local scales. For example, the Little Snake River Canyon beginning at RK 14 creates a bedrock control which results in a mild sand-bed slope for several kilometers upstream. The geology thus creates 10