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r __ ~.- .. _....~,.. _ -_~ ~ r: ~:~ r. ~~=~~J _lg_ The alluvium deposits associated with the Williams Fork and Yampa Rivers within the permit area of the Eagle Mines are broad, but relatively thin. The Williams Fork alluvium is between 800 and 1,000 feet wide and 10 to 15 feet thick. The Yampa River alluvium in Big Bottom is up to 9,000 feet wide, averages 5,000 feet wide and is between 10 and 35 feet thick. The Round Bottom alluvium is similar to Big Bottom; it is up to 6,000 feet wide and averages 5,000 feet. The Williams fork alluvium is described as consisting of poorly sorted clay to cobble-size material. The particle size of the alluvium coarsens towards the alluvial/bedrock contact. The surficial soils consist of two to four feet of fine sands and sandy looms. The rock strata subcropping beneath the Williams Fork alluvium within the permit area consists of the sandstones, siltstones, shales and coals of the upper Iles Formation and the lower Williams Fork Formation. The alluvium of the Yampa River in the Big Bottom and Round Bottom is described as consisting of sandy silts overlying poorly sorted silts, sand and cobble-size stream sediments with occasional layers of clean sands and gravels. The alluvium of the Yampa River coarsens towards the alluvial/bedrock contact. The bedrock which subcrops beneath the Yampa River alluvium in the permit area consists of the Iles Formation through the Williams Fork Formation. These formations consist of sandstones, siltstones, shales and coals. Both the Trapper Mine and the Eagle Mines are located within the Big Bottom Syncline Basin. This syncline is a smaller structural depression of the southwestern margin of the larger Sand Wash Structural Basin. The Big Bottom Syncline is bounded on the north and east by the Buck Creek or Breeze anticline, and on the south and west by the Moffat or Williams Fork anticline and the Bell Rock Dome. The southwestern portion of the Eagle No. 5 life-of-mine area and the proposed Sugarloaf life-of-mine area lie within the Round Bottom syncline. The Round Bottom syncline is bounded on the north and east by the Moffat or Williams Fork anticline and on the south and west by the Axial Basin anticline. All of the present coal mining in the Empire Energy Mines is within the Big Bottom syncline. The 2 West area of the Eagle No. 5 Mine will extend approximately 150 acres beyond the axis of the Williams Fork anticline and into the Round Bottom Synclinal Basin. The geologic formations dip 6 to 10 degrees to the north and northeast in the area of the Trapper and Eagle Mines in Big Bottom. The western part of the Eagle Mines permit area dips 10 to 30 degrees to the southwest into the Round Bottom syncline. At the proposed Sugarloaf Mine, the strata dip 15 to 30 degrees to the east and into the Round Bottom Synclinal Basin.. The study area has undergone faulting as a result of crustal deformations related to folding. Several extensive faults (greater than 8 miles in length) cross the general area to the north and west of the Big Bottom, and to the north and east of the proposed Sugarloaf Mine. Minor faults in the general area of the Trapper and Empire Energy Mines are less than 50 feet. One large displacement fault cuts east-west through the proposed Sugarloaf Mine.