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�, measurements, physical habitat assessment, description of adjacent riparian habitats, and <br />assessment of aquatic macroinvertebrate populations upstream and downstream from the point of <br />discharge. Censusing of fish populations was not included in the study, although this report <br />summarizes what is known about the fishery in the area. <br />Description of the Study Area: <br />The study area lies on the eastern edge of the Colorado Plateau, about 15 miles southeast of <br />Grand Mesa in Gunnison County. A 1600 in stretch of the river was studied between the town of <br />Somerset and the West Elk Mine, located approximately 1 mile east of Somerset (Figure 1). <br />Adjacent to, and upstream of, the study area, the North Fork and its tributaries drain a region that <br />is mostly underlain by geologic formations of the Mesa Verde Group of Cretaceous age, and the <br />Wasach Formation of Tertiary age. The cliffs and upper slopes above the study area consist of <br />exposures and materials derived from the Mesa Verde Group. These formations consist mostly of <br />sandstones and shales. Much of the watershed above the study area is covered by loosely <br />consolidated and unconsolidated surficial deposits of glacial origin or of mass wasting that has <br />produced numerous landslides and slumps. Valley bottoms are covered by extensive deposits of <br />alluvium. As a result of the poorly competent bedrock and loose surficial deposits in the region, <br />large sediment loads are carried down the river during spring runoff. Much of the sediment is <br />trapped by the Paonia Reservoir, located about 5 miles upstream of the study area, however, the <br />river quickly turns brown from fine sediment loads during regional runoff events. <br />Immediately upstream of the town of Somerset, the river has been impacted by various <br />underground coal mining activities, recent highway construction, and hydrologic changes due to <br />t the construction and operation of Paonia Reservoir. The offices, shops, and coal storage and <br />loadout facilities of the Bear Mine are located adjacent to the lower portion of the study area on <br />the south side of the river. The offices and loadout facilities of the large West Elk mine are <br />located a few hundred meters upstream of the study area, and a holding pond for the West Elk <br />mine is situated adjacent to the river and the upstream portion of the study area on the south side. <br />Colorado Highway 133 runs through the valley and is located adjacent to the study area along the <br />north side. Railroad tracks to the West Elk loadout facility parallel the north side of the highway. <br />The Sanborn Creek Mine is located to the north of the railroad tracks. Drainage from the mine is <br />pumped into a holding pond, and the outlet from the pond flows into Sanborn Creek. From there, <br />the creek passes through a culvert under the railroad tracks and highway to the North Fork River. <br />The Mine's NPDES discharge monitoring point is located on Sanborn Creek, approximately 2 in <br />upstream of its confluence with the North Fork. Sanborn Creek is a small, apparently intermittent <br />stream. Flows were estimated to be less than 200 gpm during the times CSM investigators visited <br />the site. <br />About five years ago, the Colorado Department of Transportation completed extensive <br />reconstruction of Highway 133 east of Somerset. During the reconstruction project, the highway <br />was widened, straightened, and the riverbank adjacent to the highway was stabilized with <br />2 <br />