The Trapper Mine is located in the Yampa coal field that is composed of coal-bearing rocks that are Upper Cretaceous in age. The coal-bearing rocks mainly outcrop south of the Yampa River in northwest Colorado. The Yampa coal field extends east to west about 50 miles (80.5 km) and is about 40 miles (64.4 km) north to south.

The surface bedrock in the Trapper Mine Project Area is mainly the Upper Cretaceous Williams Fork Formation, which is part of the Mesaverde Group, a regional unit that contains a large coal resource in northwest Colorado (Brownfield and Johnson 2008). The Williams Fork Formation consists of interbedded sandstones, siltstones, shale, and coals and crops out along a six-mile-wide (9.7-km) belt that extends along the entire length of the Williams Fork Mountains (Tweto 1976). The Williams Fork Formation is underlain by the Illes Formation, also part of the Mesaverde Group. The Illes Formation is lithologically similar to the Williams Fork Formation consisting of sandstones, mudstones, carbonaceous shale, and coal (Brownfield and Johnson 2008). The Lewis Shale, which is stratigraphically higher than the Mesaverde Group, outcrops in the northern extremity of the SMCRA permit area. The Lewis Shale also is Upper Cretaceous in age and is composed of uniform dark-gray marine shale, but also contains thin sandstones (Johnson 1987; Tweto 1976). Surficial deposits consist of alluvium, residuum derived from the Williams Fork Formation and the Lewis Shale, and ........

The Trapper Mine uses a combination of dragline, truck shovel, and highwall mining methods to remove the overburden and mine the coal. Coal mined at the Trapper Mine is delivered by truck to the Craig Station at an average rate of approximately 2.3 mtpy (with a maximum rate of 2.6 mtpy). The coal is mined from seven coal seams of the Upper Williams Fork Formation: the “H,” “I,” “K,” “L,” “M,” “Q,” and “R” seams. Within the Project Area, the “R” seam is too deep for surface mining. Draglines were the primary earthmoving equipment used until October 8, 2006, when a 250-acre landslide occurred within the Project Area. Following the landslide, mining has been accomplished by a combination of dragline, dozer, and truck and loader operations, depending on the depth and material being mined. The overburden, or rock that lies above the coal seams to be mined, is drilled and blasted to break up the rock to allow it to be moved using the mining equipment. Blasting is performed using an ammonium nitrate and fuel oil (ANFO) mixture. After overburden blasting is completed, the overburden removal begins. For the Project Area, overburden removal would occur primarily using trucks and loaders. The maximum coal depth for the Project Area would involve the initial use of trucks and loaders because the draglines cannot economically remove materials deeper than 200 feet. The overburden ranges in depth from 100 to 150 feet. Following removal of overburden by the trucks and loaders, dozers scr ........

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