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Important attributes of the historical river Flow variability on the Colorado River ranged widely from 0.5 to 7100 m's-' at Yuma, Arizona (Dill 1944). Canyonbound confined reaches were subject to large vertical water surface variations, thus most canyon reaches historically had large, annually mobilized sand bar deposits. Regular high flows kept the channel free of encroaching vegetation by scouring shorelines and removing newly established seedlings. Renowned for dangerous rapids, these areas include Lodore Canyon on the Upper Green River; Yampa Canyon, on the lower Yampa River; Whirlpool and Split Mountain Canyons, below the Yampa and Green River confluence; Desolation and Gray Canyons above Green River, Utah; Cataract Canyon below the Green and Colorado River confluence; and the Grand Canyon below Glen Canyon (now Lake Powell). The following first-hand look at the unexplored middle Green River by John Wesley Powell is particularly insightful and prophetic and provides important perspective on habitat available to native fishes on the Green River. June 29, 1869 (Powell 1875, p.38) "The course of the river for much of the distance, is through canyons; but at some places, valleys are found. Excepting these little valleys, the region is one of great desolation: arid, almost treeless, bluffs, hills, ledges of rock, and drifting sands. Along the course of the Green, however, from the foot of Split Mountain Canyon to a point some distance below the mouth of the Uinta, there are many groves of cottonwood, natural meadows, and rich lands. This arable belt extends some distance up the White River, on the east, and the Uinta, on the west, and the time must soon come when settlers will penetrate this country, and make homes." The Uinta is now known as the Duchesne River. On June 27, 1869, Powell provides a description of the river bottoms between Jensen and Ouray, Utah near an area known as Horseshoe Bend. 3