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• Gemmormholoov. The areas (First and Second Park) in which the Nucla Mine mining area is situated <br />were formed by a regional uplift of sedimentary rocks with the uppermost strata being the <br />Cretaceous Dakota sandstone and Burrow Canyon formations. The formations are overlain by <br />varying thicknesses of undifferentiated eolian silts and sands. These deposits have subsequently <br />been reworked by water, forming rolling upland valleys that are dissected by both Tuttle and <br />Calamity Draws. Since completion of the Colorado Cooperative Company's main irrigation ditch <br />around 1910, the unconsolidated deposits have been further reworked by man to form broad rolling <br />valleys across the first and second park, making the area more conducive for irrigation and <br />agriculture. <br />Nucla Mine is located on a gently sloped upland azea on the north flank of Tuttle Draw in the <br />southern portion of the Second Park. It is situated entirely within the Tuttle Draw Watershed (14.5 <br />square miles). Tuttle Draw watershed is an upland drainage area that is tributary to the San Miguel <br />River, consisting primarily ofpinyon-juniper woodland and mountain scrub/brush types of vegetation. <br />The portion of the watershed that lies in the Second Park area is mostly irrigated pasture and <br />Sagebrush rangeland. The watershed has a dendrific drainage pattern with steeply incised <br />ephemeral side fributaries, except for areas in the vicinity of irrigation, which intermittently carry <br />irrigation return water. Tuttle Draw near the Nucla Mine is a meandering perennial stream (due <br />to irrigation return flow occurring in the area) with a narrowly incised channel up to four feet in depth. <br />• There are limited primary terrace areas directly adjacent to the channel. Valley bottom widths are <br />from less than 100 feet to about 500 feet consisting of poorly reworked unconsolidated sVeamlaid <br />deposits with isolated pockets of weathered colluvium. In the reconnaissance investigation study, <br />about 20 acres along Tuttle Draw were found to be underlain by unconsolidated streamlaid deposits. <br />These areas are not considered extensive enough for effective irrigation. <br />ltrigatifln. The area in the vicinity of Nucla Mine has (since about 1910) had an extensive man- <br />made irrigation system. The water used for flood irrigation is diverted from the San Miguel River <br />approximately 15 miles east of the Nucla Mine by the Colorado Cooperative Ditch Company. The <br />irrigation ditches Vansect basins and commonly run along the basin divides (see F~chibit 7-1 for the <br />exact location of the irrigation ditches). The main irrigation ditches have a network of feeder ditches <br />running from them for irrigating outlying fields. These ditches are a source of ground water <br />recharge, causing ground water mounding in the shallow ground water aquifer system. The effects <br />of mounding near the Nucla Mine are apparent from monitor well water levels and hydrographs (see <br />Appendix 7-2). Perennial flow occurs in Tuttle Draw as a result of ground water discharge and <br />return flow from the irrigation of the upland area. Site inspections confirm that water used for <br />irrigation is obtained from the San Miguel River and no flood irrigation water is obtained from Tuttle <br />Draw or Calamity Draw. <br />• <br />16-8 <br />