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-10- The Orchard Valley mine lies on the southeast margin of the Piceance Basin. Sedimentary rocks ranging from late Cretaceous to early Tertiary age, and dipping 5 degrees North, are exposed in the mine areas. Structural-stratigraphic cross-sections are presented on Maps 41, 42 and 44 in Volume 9, and the mine area geology is presented on Map 49. Coal is to be produced from the Mesaverde Formation, a 2,500-foot-thick sequence of sedimentary beds overlain by the Ohio Creek Congolomerate and underlain by the Mancos Shale. The Mesaverde Formation is composed of four members; the Rollins sandstone, the Upper and Lower Coal members, and the "Barren" member. The lowermost member of the Mesaverde Formation, the Rollins sandstone, is a white to buff-colored, well-sorted, medium-grained sandstone, ranging from 150 feet to 200 feet thick in the permit area. The Lower Coal member overlies the Rollins sandstone and consists of interbedded sandstones, siltstones, coals, and shale. The unit averages 265 feet thick in the permit area and bears three significant coal seams--the "A", "B", and "C" seams. The Upper Coal member is approximately 220 feet thick, containing shales, siltstones, sandstones, and the "D", "E", and "F" coal seams. The Orchard Valley mine will be located in the lowermost seam, the "D" seam. At the mine site, the coal is immediately overlain and underlain by shale. See figure 2.04.1, Typical Lithographic Section Roof and Floor Rock of the "D" seam, page s4, Section 2.04 of Volume 8. The "U" seam overburden ranges from approximately 50U feet to 2,000 feet within the permit area. The thickness of this seam decreases from 26 feet at the outcrop to 8 feet at the northern edge of the permit boundary. The "D" seam dips from the outcrop area in the South five degrees to the North, and the strike is North 88o West. Overlying the upper Coal member is the Barren member of the Mesaverde Formation. This unit consists of interbedded and lenticular sandstones, siltstones, and shales of varying thicknesses. This unit is thought to be of terrestrial origin and, as a result, the sandstones and the coals are highly lenticular, discontinuous, and of limited lateral extent in outcrop. This unit ranges up to 1,500 feet thick and outcrops throughout the southern portion of the permit area. Three categories of potential aquifers occur in the general area. These are alluvial and terrace deposits associated with the North Fork of the Gunnison River, the localized shallow alluvial areas in the Stevens Gulch and Terror Creek drainages, and ground water in the lenticular sandstones and the Rollins sandstone of Mesaverde Formation.