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colluvium, and landslide deposits. Anthropogenic fill (man-made) was used as the map unit for some of <br />the larger earthfill embankments. Alluvium was mapped in areas where the floodplain was broad and it <br />was clear that few of the deposits in the valley bottom were related to the immediately adjacent valley <br />slopes. Typically, the alluvium in the broader floodplain areas contained more sand and gravel than was <br />present in the valley fill and other deposits. <br />Valley fill deposits, as used on the geologic map, comprise alluvium, colluvium, fan deposits, and <br />landslide deposits. In the upland areas along Dry and Sage Creeks, the valley bottoms consist of more <br />than just alluvium, and hence the term valley fill was chosen. This usage is consistent with the U.S. <br />Geological Survey mapping of the area (Madole, 1989). <br />Where possible, fan deposits were mapped based on the geometry of these geomorphic features as <br />observed on aerial photographs and field inspection. Fans are deposited in this area at the mouths of <br />intermittent tributary streams. <br />Colluvium was mapped where these deposits appeared to be more than five feet thick and it was clear <br />that the principal mechanism of transport was gravitational. Landslide deposits were mapped where <br />there was geomorphic evidence of slope failure and the resulting deposits were present. This term <br />encompasses a broad variety of slope failure types, including debris flows, slumps, and earth flows. <br />Dry and Sage Creeks are intermittent streams that contain sediment that is only infrequently in <br />transport. Sediment from the valley slopes has built up and has yet to be removed. Former floodplains <br />are stranded on the order of 5 to 15 feet above the current stream channel bottoms. This channel <br />incision is probably in part related to major flooding that occurred as recently as 1985. However, even <br />this flooding failed to remove a significant portion of the sediment stored in the channel. As the <br />floodplains reestablish, these incised channels will be widened. This means that further erosion will <br />encroach on the areas potentially available for agriculture. <br />Streams with sufficient carrying capacity are able to accommodate the inflow of sediment to the <br />channel and transport this sediment downslope. The stream determines the channel position in its <br />floodplain. However, in Dry and Sage Creeks, the channel course is frequently determined by the <br />presence of fans from tributaries and landslide deposits, indicating that there is insufficient discharge to <br />carry the available sediment load. <br />The fan in the east central portion of Section 4 (T5N R88W on Dry Creek) is an example of one that <br />has determined the course of the creek because of the volume of sediment entering the creek from the <br />tributary. The landslide in the southeast portion of Section 35 (T6N R88W) on Sage Creek is an <br />example of a slide that originally blocked the drainage and then later was breached. <br />As shown on Exhibit 16-3 (Land Use and Irrigated Areas Map), there are a few areas that are currently <br />. under cultivation in the upland areas of Dry and Sage Creeks. Exhibit 16-3A provide new AVF <br />14 Revised 9/98