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• bankful width and depth of 30 feet and 4 feet, respectively. In <br />places the active channel has cut about 18 feet into the alluvial <br />deposit whose total thickness is estimated at 25 feet from <br />records for the Rockvale municipality wells ([able 2.04.5-2). <br />The alluvial deposit is composed of mainly dark grey silt and <br />clay but a gravel bed that yields eater to the yells ie expected <br />to lie at the base. <br />2.0 Lewis Gulch <br />All surface runoff from the portal of Twin Pines No. 2 Mine <br />will flow into Lewis Gulch, a small channel which apparently has <br />not flowed in several years. The channel sides and bottom are <br />for the most part rocky and choked with old mine dumps (fig. <br />2.04.7(2)-1, 2.04.7(2)-2, and 2.06.8-4). After the confluence <br />with a small tributary from the northwest (Dry Gulch?) the <br />channel bottom is relatively wider, smoother and much lees <br />disturbed. <br />r1 <br />U <br />During the field reconnaissance study no moisture vas <br />observed along Lewis Gulch. It appears that, in fact, no surface <br />runoff has taken place for some time (2.04.7(2) Surface Water <br />Information). There is no evidence of subirrigation and the <br />vegetation cover consists of pinyon and juniper bushes and trees <br />on the steep rocky sides and blue grams grass along the gentler <br />elopes. <br />The alluvial fill in Lewis Gulch is less than 50 feet wide <br />and less than 10 acres in area and thus, does not fulfill the <br />geomorphic requirements of an alluvial valley floor. Upstream <br />from Section D (see drawing of General Mine Area) rock outcrops <br />border the aides of the narrow active channel. Even where the <br />channel widens out immediately downstream of Section D, a large <br />portion of the unconsolidated material is talus deposit rather <br />than alluvium. Further downstream and nearer to the confluence <br />. vith Oak Creek, the valley widens and [he alluvium becomes <br />thicker as a result of the influence of Oak Creek. There are no <br />domestic or agricultural surface-eater users in Lewis Gulch. <br />JFSA-75 <br />