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<br />O~!~M <br /> <br />-4- <br /> <br />The main arable land mass of the valley is on an average of <br />50 to 100 feet higher than the River. This lend is made up of henohes. <br />mesas and the long slope of the eastern side of the valley. These areas <br />are out by thB channels of the River end of tributary streams and array- <br />as which v.ould be normally dry except for irrigation returns end WIl.ste. <br />The JneSo.s at the lo~r end of the valley drop off abruptly to the Gunnison <br />River bottom lands. <br /> <br />On the vest the valley is bounded by a portion of the Unoom- <br />pahgre Plateau. This Plo.teau is a prominent uplift extending from the <br />San Juan llountains northward. terminating ""st of Grand Junction, some <br />40 miles north of Delta. It rises on a gentle slope from the vest edge <br />of the tril!Ulgular valley to an elevation of about 8.400 feet 30 miles <br />west of Delta and to its high point (10.338 feet) at Horsefly Peak. The <br />swmni t ridge of the Plateau forms the drainage boundary between the <br />Gunnison end Dolores Rivers. The vest side of the Plateau breaks sharp- <br />ly into the Dolores Basin. Deeply eroded cenyons mark the fo.oe of the <br />Plateau. Only the southeastern end of the Plateau lies in the Uncom- <br />pahgre drains.ge. The remainder is drained by strellIlls directly tributary <br />to the Gunnison River. The most easterly of this group of strellIlls is <br />Rouhideau Creek which hends at a point 23 miles due west of Colona. run- <br />ning in a northerly direction. and emptying into the Gunnison 4-1/2 <br />miles west of Delt,.... The east rim of the Roubideau Cenyon forms the <br />""st houndary of the Uncanpahgre Basin until the divide swings away from <br />the oanyon rlm to the northeast toward Delta. This break ave.y from the <br />canyon starts about 13 miles vest of Montrose. (See Plate II). This <br />oreates a triangular area in the northwest corner of the study area. <br />lying next to Roubideau Creek. whioh is direotly. tributary to the <br />Gunnison. Similarly there is a triengular area in the northeast corner <br />of the area which is also tributary to, the Gunnison. <br /> <br />4. Gradients I <br /> <br />Table 2 gives the gradients along thB Unoanpahgre River. <br /> <br />Table 2 <br /> <br />RIVER AND VALlEY GRADIENTS <br />UNCOMPAJIGRE BASUi <br /> <br />Section <br /> <br />River Gradient <br />(Feet per Hile) <br /> <br />Valley Gradient <br />(Feet per lIile) <br /> <br />1. Souroe to Ouray <br />2. Ouray to Colona <br />3. Colona to Montrose <br />4. tlontrose to 01o.the <br />5. Olathe to Delta <br /> <br />720 <br />62 <br />55 <br />42 <br />37 <br /> <br />50 <br />45 <br />35 <br />