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4-4f <br /> <br />Mancos shale. The valley sides are formed either by bedrock <br />outcrops or by colluvial soils. In addition to the bedrock, <br />several alluvial fans of important dimensions have been identi- <br />fied on the site. They cover the alluvial deposits of the East <br />Salt Creek and would not qualify as AVF. <br />At one location, at the west side of the East Salt Creek valley, <br />close below the confluence of the McClane Creek, a distinct <br />remnant of an old and high river terrace was identified. It <br />was found in the road cut; it is about 20 feet high above state <br />Highway 139 and consists of distinct horizontal layers of well- <br />rounded gravel, interbedded with several layers of silty clays. <br />• <br />In addition to these geologic formations, a large man-made fill <br />was mapped and indicated on Figure 4.1-2. It is a large earth- <br />fill dam constructed across the East Salt Creek valley close <br />below the confluence with the ephemeral channel in McClane Canyon. <br />WATER AVAILABILITY <br />EAST SALT CREEK VALLEY <br />According to. pertinent regulations, the alluvial valley floors <br />have to have a water volume sufficient for subirrigation or <br /> <br />.. flood irrigation. There is enough evidence that the alluvium <br />of the East Salt Creek complies with these conditions. Apart <br />of the valley below the McClane Canyon has traditionally been <br />irrigated with a system of diversion ditches, contour ditches <br />and graded borders. The irrigated portion of the valley stretches <br />