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northeast litnb of the Moffa[ Anticline dips northward into [he Big Bottorn syncline.. Although <br />only small-displacement gravity faults have been found in the permit area, the lazge displacement <br />Moffat thrust fault probably lies several thousand feet beneath the ground surface of the permit <br />area. The surface trace of the Moffat thrust is two miles southwest of the permit area. <br />Local Coal Mining History. Previous training within the Eagle Mines permit area included: the <br />Fields Mine which operated in the E seam during the 1930s: the Wise Mine and the Wise Hill <br />No. 2 which operated in the C seam (below the E seam) in the 1940s and l9~Os; the L,eo White <br />and Baker iVlines which operated in the Hart seam (between the F seam and Twentymile <br />sandstone); and the Wise Hill Nos. 3 and 4 ,which operated in the Hart seam during the 1970s. <br />Surface Water Features. Drainages within and adjacent to the permit area (on the north-facing <br />slope) are ephemeral and generally extend south to north down the slope in a dendritic pattern. <br />These drainages flow primazily in response to snowmelt or heavy rains. Flows in these drainages <br />that do not infiltrate into the ground or evaporate eventually enter the Williams Fork River, and <br />then flow the short distance to the confluence with the Yampa River in t:he northwest comer of <br />the permit area. <br />Yampa River Flows. Flow in the Yampa River depends primarily on snowmelt from the winter <br />snowpack on the high mountain slopes surrounding the drainage basin. The lower intermittent <br />and ephemeral drainages produce only a small part of the total water yield of the basin (Colorado <br />Water Conservation Board, 1969). About 64 percent of the flow occurs in May and June with up <br />to 84 percent occurring from April [o July at selected gaging stations within the drainage basin <br />(Steele, et al., 1979). Minimum flows generally occur from August through February. Irons, et <br />al. (1965) reported that summertime flows in streams of the basin from .July through October <br />generally include a large component of ground water dischazge. Extremes recorded at the <br />Maybell Gaging Station are a maximum flow of 17,900 cfs on May 19, 1917, and a minimum of <br />2.0 cfs on July 17-19, 1934. Annual variation in yield may also be great. Historical annual yield <br />has varied from 345,000 acre-feet in 1977 to 2,135,000 acre-feet for the Yampa River in 1917. <br />Average annual yield amounts to 1,116,000 acre-feet. <br />Williams Fork River Flows. The Williams Fork River is a major tributary of the Yampa River. <br />The Williams Fork drains approximately 350 square miles, or ten percent of the Yampa River <br />Valley. The Williams Fork fluctuates seasonally like the Yampa, but is more dependent on <br />snowmelt, and there is less ground water discharge to sustain the flows of the river during low <br />flow periods. Flows in the Williams Fork in the permit area typically range between 2500 cfs <br />during spring runoff and less than 100 cfs during low flow. <br />Yampa River Sediment Load. In addition to yield, water quality also varies seasonally. Total <br />suspended sediment loads are at a maximum during peak flows associated with spring runoff. <br />Steele et al. (1979) reports that up to 90 percent of the annual sedimeN: load of the Yampa River <br />at the Maybell Station is dischazged during the period of snowmelt runoff. Total suspended <br />sediment loads increase with increased discharges (flows) in the rivers. Dissolved solids loads <br />show an inverse relationship with stream dischazges. <br />