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• the San Miguel River to mitigate any impacts that may occur. Refer to the CDMG's Nucla Mine Proposed Decision and findings of Compliance Document (1983) for the results of their study. The discussion that follows is based on information contained in Section 2.04.7, field observations, and interpretation of false-color infrared and color aerial photographs at scales of 1" = 500'. Geomorphology The areas (First and Second Park) in which the New Horizon Mine and the New Horizon 2 mining area are situated were formed by a regional uplift of sedimentary rocks with the uppermost strata being the Cretaceous Dakota sandstone and Burrow Canyon formations. The formations are overlain by varying thicknesses of undifferentiated eolian silts and sands. These deposits have subsequently been reworked by water, forming rolling upland valleys that are dissected by both Tuttle and Calamity Draws. Since completion of the Colorado Cooperative Company's main irrigation ditch around 1910, the unconsolidated deposits have been further reworked by man to form broad rolling valleys across the First and Second Park, making the area more conducive for irrigation and agriculture. The New Horizon 2 mining area is located entirely within the Calamity Draw watershed (7.0 square • miles) which is less than half the size of the Tuttle Draw watershed. Calamity Draw is also an upland drainage area that is tributary to the San Miguel River. The middle and upper portion of this watershed (the First Park) has been intensively irrigated and cultivated since about 1910. Presently, the watershed is comprised of irrigated pasture, rangeland, and the town site of Nucla. Agricultural and irrigation practices have resulted in a disjointed tributary drainage pattern which is almost completely controlled by the return ditches of the irrigation network. Most of the tributaries, especially in the mid and upper portion of Calamity Draw, are intermittent with flow being controlled by the timing and application of irrigation water. Calamity Draw, in the vicinity of the New Horizon 2 mining area, is a perennial, meandering stream with a narrow incised (up to three feet) channel. The banks are stable as a result of vegetation encroachment. Calamity Draw has the same valley bottom widths and geomorphic features as Tuttle Draw, but is less steep and confining. The perennial flows of both draws are due to irrigation return water and the limited baseflow is maintained by overburden ground water discharge. The overburden aquifer is recharged from the upland irrigation system. Irrioation • (REVISED 6/01) 2 . O5 . 6 (3) - 12