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Rulison-DeBeque (Stratum 11): The uppermost study reach extends 37 river kilometers (RKM) from Rulison, CO, to the head of DeBeque Canyon (RKM 365-328). In this reach, the Colorado River flows through a wide alluvial valley underlain by shales and sandstones of the Green River Formation (Cashion, 1973). Locally the river channel is bounded by Pleistocene pediments and strath terraces. The active floodplain is up to 1 km wide in many areas. Mature stands of native cottonwood trees (Populus deltoides) are common on the floodplain, along with shrubs such as willow and sage. Non-native species such as tamarisk (Tamarisk chinensis) and Russian olive (Elaeagnus angustifolia), are much less abundant in this reach than in reaches downstream. The average bankfull width of the river is 114 m, the bankfull depth is 2.45 in, the average slope is 0.00196, and the bed material is gravel with a median grain size, D50, of 57 mm (Table 1). DeBeque Canyon (Stratum 10): DeBeque Canyon begins at RKM 327, about 10 km downstream of DeBeque, and ends upstream of Palisade at RKM 298. DeBeque Canyon is a relatively shallow canyon cut into interbedded shales and sandstones of the Hunter Canyon Formation (Cashion, 1973). This reach is more influenced by engineering structures than any other reach in the study area. Interstate highway 70 borders much of the left bank, a rail line borders much of the right bank, and there are three diversion dams within the canyon. Nonetheless, a narrow floodplain is present along one or both banks, thus we classify this reach as quasi-alluvial. The average slope through DeBeque Canyon is 0.0015, the bankfull width is 77 in, the bankfull depth is 3.1 in, and the bed material consists of gravels and cobbles with an average D50 of 52 mm (Table 1). 15-mile reach (Stratum 9): The 15-mile reach extends for a distance of 24 km from the town of Palisade (RKM 298) to the confluence of the Gunnison River in Grand Junction (RKM 275). We classify this reach as fully alluvial (Table 1), although in many places the left bank is bounded by Mancos shale. This reach and the adjacent 18-mile reach are in urbanized areas where the channel has been modified to varying degrees by gravel mining operations and bank revetments (levees and rip-rap); however, our field mapping of these reaches indicates that levees and rip-rap form much less of the channel boundary than is commonly thought. Floodplain characteristics and vegetation vary widely in this reach. Dense thickets of tamarisk, Russian olive and willow are common, as are open stands of cottonwood. The average slope of the 15-mile reach is 0.00175, the bankfull width is 134 m, the bankfull depth is 2.5 in, and the bed material consists of gravels and cobbles with an average D50 of 58 mm (Table 1). 18-mile reach (Stratum 8): The 18-mile reach extends for 35 km between the confluence of the Gunnison River and the head of Horsethief Canyon, near Loma, CO (RKM 246). This reach possesses many of the same characteristics as the 15-mile reach described above. The average slope of the 18-mile reach is 0.0013, the average bankfull width is 175 in, the average bankfull depth is 3.0 m, and the bed material is gravel and cobbles with a D50 of 52 mm (Table 1). Ruby-Horsethief Canyon (Stratum 7): Horsethief and Ruby Canyons form a continuous quasi- alluvial reach extending from the western edge of the Grand Valley, near RKM 245, to the entrance to Westwater Canyon, near RKM 201. This reach is bounded by resistant sandstones of the Wingate and Entrada formations, and is more incised than the two reaches immediately upstream. However, a small floodplain covered with dense tamarisk shrubs interspersed with mature cottonwood trees is present along most of the reach, even in areas with steep sandstone walls. The average slope of the reach is 0.0010, the bankfull width is 129 in, the bankfull depth is 3.64 in, and the bed material is gravel with a D50 of 47 mm (Table 1). 7