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dendritic. Tributaries to Tuttle Draw in the upper portion and near the mouth are <br />• ephemeral, and usually emanate from steep narrow side canyons. In the vicinity of the <br />mine, tributaries to Tuttle Draw commonly transport irrigation return water from pastures <br />and haylands that have been intensively irrigated since about the 1910's. The average <br />basin slope of this watershed has been calculated to be approximately 89 feet per mile, <br />with an average basin elevation of 6020 feet above MSL. <br />Tuttle Draw in the vicinity of the Nucla Mine is a meandering perennial stream, featuring <br />~- <br />a narrow and incised channel (up to 4 feet deep). The limited primary terrace areas <br />directly adjacent to the channel range in total valley bottom width from less than 100 up <br />to about 500 feet. The valley bottom is largely comprised of unconsolidated streamlaid <br />deposits, with isolated pockets of weathered colluvium. <br />The Nucla East mining area is located entirely within the Calamity Draw watershed. The <br />drainage area of Calamity Draw to its confluence with the San Miguel River is about 7.0 <br />square miles, less than half the area of Tuttle Draw. With the exception of the lower <br />portion of this basin (near the mouth), the watershed is largely comprised of irrigated <br />pasture and rangeland (First Park) and to a lesser extent, the townsite of Nucla, <br />Colorado. The middle and upper portions of Calamity Draw Basin have been intensively <br />irrigated and cultivated since the early 1920's and late 1910's. The development of the <br />townsite and corresponding spread of cultivated and irrigated fields has resulted in a <br />disjoint tributary drainage pattern almost completely controlled by the return ditches of <br />the irrigation network. These return ditches (tributaries) in the mid- and upper portion <br />of Calamity Draw are mostly intermittent and possibly perennial and are largely influenced <br />by the timing and application of irrigation water. The overall average basin slope of <br />Calamity Draw is about 76 feet per mile, with an average basin elevation of S,B57 feet <br />above MSL. For the basin area in Calamity Draw above the location of surface water <br />monitoring Site SW-N103 (see Exhibit 7-1, Hydrologic Monitoring Site Location Map), the <br />average basin slope is approximately 48 feet per mile. This suggests that since the onset <br />of man's activities in the upper portions of Calamity Draw (cultivation of land and the <br />establishment of the townsite), these activities have greatly influenced the basin <br />geomorphology of this watershed. <br />Calamity Draw in the vicinity of the Nucla East mining area is a meandering, perennial <br />stream, featuring a narrow and incised channel (up to 3 feet deep). The limited primary <br />terrace areas directly adjacent to the Calamity Draw channel range in width similarly to <br />7-107 Revised 04/11/88 <br />