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ppm. These streams flow largely over the Glen Canyon Croup and the Dakota Formation. <br />• Historic water quality samples taken at Naturita, Colorado indicate that the San Miguel <br />River has a weighted average TDS of 316 ppm and an average TDS discharge of 101 tons per <br />square mile. Specific conductance ranges between 318 and 730 umhos, and the mean Sodium <br />Adsorption Ratio (SAR) is about 0.7. Based on these values, waters of the San Miguel at <br />Naturita are classified as C2-51, which categorizes the San Miguel River as being good for <br />irrigation use. <br />As of 1957, approximately. 15,000 acres underlain by Dakota sandstone were actively <br />irrigated between Placerville and Naturita, Colorado (lorns, et al. 1965a). Using historic <br />streamflow information, lorns et al. (1965a) estimated a water budget for the San Miguel <br />River in this vicinity, and concluded that the TDS contribution to the San Miguel River <br />from irrigation is about 2.8 tons/year per acre of irrigated land. As of 1957, waters of <br />the San Miguel River (except at the mouth during low flows) were suitable for domestic <br />use, while during low flow, high levels of sulfate would render the water unsuitable. <br />Site Specific Surface Water Information <br />• Drainage Basin Geomorphology. Exhibit 7-1 delineates the areas named First and Second <br />Park. The Nucla Mine is located on the gently sloped upland just north of Tuttle Draw, in <br />the southern portion of the Second Park. The Nucla East mining area ,includes the mildly <br />sloping upland area immediately north of Calamity Draw, located approximately in the <br />middle of the First Park. Bath the First and Second Parks are relatively flat (gently <br />sloping) areas formed by regional uplift of sedimentary rocks that have been subsequently <br />dissected by both Tuttle and Calamity Draws. Both Parks consist primarily of recent <br />deposits of undifferentiated eolian silts and sands that overlay the Dakota and Burro <br />Canyon Formations. With the completion of the Colorado Cooperative Company's Main <br />Irrigation Ditch in about 1910, these deposits have been intensively reworked by <br />cultivation using irrigation water to form a broad rolling valley across the First and <br />Second Parks. <br /> The Nucla Mine is situated entirely within the Tuttle Draw watershed. The drainage area <br /> of Tuttle Draw to its confluence with the San Miguel River is approximately 14.5 square <br /> miles. The watershed in the upland area is largely covered with pinyon-juniper and <br /> mountain brush vegetation. In the lower porti ons (Second Park) the watershed is mostly <br />• irrigated pasture and rangeland. The overall drainage pattern in Tuttle Draw is mostly <br />7-106 Revised 04/11/88 <br />