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Regional C[inaate. The climate of the region is classified as highland continental, and is <br />characterized by low precipitation, large fluctuations in diurnal temperatures, low humidity, <br />moderate wind, and high levels of insolation (exposure to sunlight). The (~raig azea is in the <br />rain snow shadow of mountain ranges to the west and south and consequently has a high number <br />of dry, clear days. <br />Loca! Climate. The climate of the Craig, Colorado area is characteristic .if semi-azid steppe <br />regions. The average annual precipitation for the town of Craig, 6 miles northeast of the Eagle <br />Mines, is 13.5 inches of which over one-third is snowfall (averaging 66.5 inches/year). Average <br />annual precipitation at the Trapper Mine, next to the Eagle Mines, is 16.7 inches. The mean <br />annual temperature in Craig is 43~F, with recorded extremes of -4S~F and +]OO~F. Winds are <br />predominantly from the west, but are locally modified by topographic Features. The growing <br />season for the area azound Craig averages 77 days. <br />Physiographic Setting. The portals of the Eagle Mines are driven into the steep-sided walls of <br />the valley that the Williams Fork River has cut through the west end of the Williams Fork <br />Mountains. The mines' facilities area is in the bottom of the valley. The e;levation of the valley <br />bottom is 6,150 ft. From the valley bottom, the permit area extends up to the crestal ridge of the <br />Williams Fork Mountains. The crest of the Williams Fork Mountains fonns a ridge extending <br />about 30 miles east-west at elevations between 7,400 and 7,800 feet. The Williams Fork River <br />crosses through the mine permit area and flows into the Yampa River in the northwest corner of <br />the permit azea. The Yampa River is one of the lazgest tributaries of the upper Colorado River <br />system. <br />Stratigraphic Setting. Bedrock at the ground surface in the Eagle permit azea is a sequence of <br />sandstones, siltstones, shales, and coals that are part of the Cretaceous-age Williams Fork <br />Formation. The Williams Fork Formation is part of the Yegionally extensive Mesa Verde Group. <br />The Williams Fork Formation crops out along asix-mile wide belt that e;ttends along the entire <br />length of the Williams Fork Mountains. The Williams Fork Formation is subdivided into the <br />following three units (in ascending stratigraphic order): the lower Williars Fork, the Twentymile <br />sandstone, and the upper Williams Fork. Approximate thicknesses are: lower Williams Fork, <br />840 ft.; Twentymile sandstone, 120 ft.; and upper Williams Fork, 850 ft. Unconsolidated alluvial <br />deposits of Quaternary age fill stream drainages in the permit area and surrounding areas. The <br />alluvium is thickest in the Yampa and Williams Fork River valleys. <br />Coal Seam Stratigraphy. The coal seams mined at the Eagle Mines aze in the lower and upper <br />units of the Williams Fork Formation. Each seam is less than 10 feet thir_k. The No. 5 Mine <br />removes coal from the P seam in the upper Williams Fork Formation. Tl~e No. 9 Mine removes <br />coal from the F seam in the lower Williams Fork. The No. 6 Mine was planned to mine coal <br />from the E seam in the lower Williams Fork. (The adjacent surface pits of the Trapper Mine take <br />coal from the upper Williams Fork. The I seam of Trapper probably con~elates to the P seam of <br />the Eagle No. 5.) <br />Geologic Structural Setting. The mine is situated on the northeast flank. of the northwest <br />plunging Moffat Anticline. The Moffat Anticline is part of the larger-sc:~le Axial uplift that <br />extends northwestward across northwest Colorado to the Uinta Mountains in northeast Utah. The <br />