Laserfiche WebLink
is difficult to differentiate from the Dakota in this area and is commonly considered <br /> hydrogeologically similar. The Jurassic Morrison Formation below is composed of 250 feet to <br /> 600 feet of varicolored siltstones and mudstones with beds of limestone and sandstone. <br /> The NHM primarily produces coal from the Lower Dakota coal seam and utilizes the Upper <br /> Dakota coal seam when the seam is thick enough and of sufficient quality. The lower Dakota coal <br /> seam ranges in thickness from 4.2 feet to 6.9 feet and is 99 feet above the top of the Burro Canyon <br /> Formation. The coal dips 4.5° SW along a strike of N 45°W. <br /> C. Surface Water <br /> The San Miguel River has its source in the San Juan Mountains. These mountains are primarily <br /> composed of Tertiary volcanic rocks. Irons et. al. (1965a) has shown these waters to be of a <br /> calcium bicarbonate-sulfate type during high flow periods. These waters contain less bicarbonate <br /> during low flows while the calcium and sulfate concentrations increase due to less dilution from <br /> snowmelt runoff. The San Miguel River traverses the interior portions of a basin that is chiefly <br /> underlain by Dakota Sandstone, the Morrison Formation and Mancos Shale. The Morrison <br /> Formation and Mancos Shale have the greatest potential for influencing the river water chemistry. <br /> The San Miguel River drains an area of 1,080 square miles. In addition, approximately 15,500 <br /> acres of irrigated land lies between Placerville and Naturita, Colorado. It is estimated that 2.8 tons <br /> of Total Dissolved Solids (TDS) per acre are contributed to the waters annually from this area. <br /> This results in increased levels of magnesium, potassium, sulfate and chloride. Water quality <br /> samples taken from the San Miguel River at Naturita, Colorado, have a weighted average of 316 <br /> milligrams per liter (mg/1) TDS. Specific conductance varies between 318 and 730 millimhos <br /> (mmhos). The mean sodium adsorption ratio(SAR)is about 0.7 at Naturita. Water curves indicate <br /> that 90 percent of the time, flow in this river exceeds 60 cubic feet per second (cfs), while flows <br /> exceed 1000 cfs about 10 percent of the time. The mean discharge of the river is 351 cfs. San <br /> Miguel River waters are suitable for domestic usage except at low flow periods when sulfate levels <br /> are high. <br /> The Colorado Cooperative Ditch Company diverts as much as 145 cfs of water from the San <br /> Miguel River approximately ten miles east of the town of Nucla. The main diversion ditch then <br /> flows westerly passing just north of the town of Nucla and then flows northwestward passing north <br /> of the NHM. Diversion ditches distribute water to mainly agricultural users in the area. Since the <br /> completion of the irrigation system for this area in about 1910, these areas have been intensively <br /> reworked for irrigated agriculture. Additional uses include domestic, municipal and stock pond <br /> consumption. <br /> The NHM is located just northwest of the town of Nucla in the mildly sloping upland area between <br /> Tuttle Draw and Calamity Draw, in the northwest corner of First Park. The surface water system <br /> is characterized by a "disjointed" tributary drainage system almost completely controlled by return <br /> flow ditches of the local irrigation network. <br /> The West Lateral irrigation ditch is part of the Colorado Cooperative Company's main ditch system <br /> that originates on the San Miguel River just upstream of Cottonwood Canyon (about 12 miles <br /> upstream of Naturita). Construction of the main ditch commenced in 1896, and water began <br /> 11 <br />