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Colluvium was mapped where these deposits appeared to be more than five feet thick and it <br />was clear that the principal mechan~i sm of transport was gravitational. Landslide deposits <br />were mapped where there was geomorphic evidence of slope failure and the resulting <br />deposits were present. 'this term encompasses a broad variety of slope failure types, <br />including debris flows, slumps, and earth flows. <br />Sage Creek is an intermittent stream that infrequently transports sediment. Sediment from <br />the valley slopes has built up and teas yet to be removed. Former floodplains are stranded <br />on the order of 5 to 15 feet above the current stream channel bottom. This channel <br />incision is probably in pzirt related to major flooding that occurred as recently as 1985. <br />However, even this floodir~g failed to remove a significant portion of the sediment stored <br />in the channel, As the floodplains reestablish, these incised channel reaches will 6e <br />widened. This means that further erosion will encroach on the areas potentially available <br />for agriculture. <br />Streams with sufficient carrying capacity ere able to accommodate the inflow of sediment <br />to the channel end transport this sediment downsLope. The stream determines the channel <br />position in its floodplein. However, in Sage Creek, the channel course is frequently • <br />determined by the presence of fans from tributaries and landslide deposits, indicating <br />that there is insufficient discharge to carry the available sediment load. The landslide <br />in the southeast portion of Section 35 (T6N R88w) on Sage Creek is an example of a slide <br />that originally blocked th? drainage and then later was breached. <br />As shown on Exhibit 16-3 (Land Use and Irrigated Areas Map), there are a feu areas that <br />are currently under cultivation in the upland areas of Sage Creek. Most of the valley <br />bottoms are used for grazing, if they ere used at all. The width of the valley bottom of <br />the upland areas of Sage Creek is rarely more than 300 feet wide and is cut by sinuous <br />channels that ere incised up to approximately 15 feet. The walls of the incised channels <br />are near vertical and the maximum widths are less than 50 feet grid often less than 20 <br />feet. .Because of the narrow end sinuous nature of the channel, farm equipment could have <br />to move frequently from on? side of the channel to another using a system of bridges. As <br />erosion proceeds, the stream will erode back the steep walls of the channel, decreasing <br />the area potentially available for farming and making temporary bridge abutments <br />susceptible to failure. <br /> <br />16-3-2 Revised 06/19/95 <br />