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STUDY AREA This study encompasses approximately 300 km of the Colorado River in western Colorado and eastern Utah (Fig. 1) (distances are given here in river kilometers, RKM, measured upstream of the green River confluence). Field measurements characterizing this segment of the Colorado River were obtained at closely spaced intervals from Rulison, CO (RKM 363), to Potash, UT (RKM 77), with the exception of two short reaches in DeBeque Canyon and Westwater Canyon that were difficult to access. These field measurements have been augmented with streamflow and sediment data from USGS gauging stations below Glenwood Springs, CO; near Cameo, CO; near the Colorado-Utah state line; and near Cisco, UT. 109'30 109°00 108'30 108'00 3e30 39°00 38'30 Rulison o • Cr. RD P`40? 7 J O DeBeque • \O`?d 9095500 i Loma I • DC 9163500 Grand Westwater RH i Junction f 16M O KEY 15M Cis WW • ? RD Rifle-DeBeque DC DeBeque Cyn 15M 15-Mile Reach CF C 18M 18-Mile Reach RH Ruby-Horsethiet Cyn ?s WW westwater Cyn DW O O' CF Cisco-Fish Ford 9180500 9L DW Dewey O- PV Professor BB PV O Valley N BB Big Bend MV I 9 MV Moab Valley Potash Moab I S 0 10 20 30 mi • I I I L 0 10 20 30 40 50 km 109°30 10900 108'30 108,00 Figure 1. Location map of study area and subreach boundaries. Hydrology 3e 3eoo 38°30 The majority of runoff carried by the Colorado River is derived from spring snowmelt in alpine and sub-alpine basins in the Rocky Mountains of central Colorado. As the river flows west, it gradually drops in elevation and begins flowing across the Colorado Plateau, a region of sparse vegetation and little rainfall. This region contributes little additional runoff, but a high proportion of the river's annual sediment load (Iorns et al., 1965; Liebermann et al., 1989). Most of this sediment is derived from surface erosion of sedimentary rocks (shale and sandstone) that are found throughout western Colorado and eastern Utah. The Colorado River thus receives its supply of water and sediment from two distinctly different sources, which contrasts with conditions in the typical dendritic drainage basin where water and sediment are supplied more or less evenly along the length of the trunk stream or river. We believe this has been an important influence on the geomorphology of the Colorado River.