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<br />La Plata Coal Draft Finings - 2 - May 18, 1987 <br />The Existing Environment <br />The proposed permit area lies in the upper rim of the San Juan Structural <br />Basin, an asymmetric structural basin in northwestern New Mexico and <br />southwestern Colorado. Sedimentary rocks within the basin are of both marine <br />and non-marine origin. <br />The formation of interest in the area of the mine site is the Cretaceous <br />Mesaverde Group. The Mesaverde Group is composed of three major units (in <br />ascending order): Point Lookout Sandstone, Menefee Formation and Cliffhouse <br />Sandstone. <br />The coal seam to be mined occurs in Menefee. This formation is composed of <br />interbedded sandstone, shale, carbonaceous shale, and coal. The La Plata <br />No. 1 will remove the upper ("A") coal seam from the Menefee during the course <br />of its operation. <br />Ground water occurs in the Nay Gulch alluvium adjacent to the mine site and in <br />the Point Lookout Sandstone underlying the penetration. The Hay Gulch <br />alluvium is nearly saturated year round. The Point Lookout Sandstone aquifer, <br />nearly 275 feet below the mine floor will be unaffected by mining operations. <br />FINDINGS <br />IV. Geology - Rules 2.04.5 and 2.04.6 <br />La Plata Coal Corporation has supplied geologic information pertaining to the <br />proposed operation and adjacent area. This information may be reviewed in <br />Sections 2.04.5 and 2.04.6 of the permit application. <br />The La Plata No. 1 Mine is located on the northwestern rim of the San Juan <br />Basin. The San Juan is an asymmetric structural basin in southwestern <br />Colorado and northwestern New Mexico. The basin contains sedimentary rocks <br />ranging in age from Cambrian to Holocene. The consolidated strata exposed in <br />and near Hay Gulch were deposited during the upper Cretaceous period. <br />The stratigraphic unit of interest is the upper Cretaceous Mesaverde Group, <br />The lowermost member of the Mesaverde Group is the 300 to 400 foot thick Point <br />Lookout Sandstone. The upper portion of the Point Lookout is a massive, white <br />to buff, cliff forming sandstone, while the lower portion becomes shalely, <br />grading into the underlying Mancos Shale. <br />The Menefee Formation, which conformable overlies the Point Lookout Sandstone, <br />is the coal bearing unit in this area. At the proposed mine site, the Menefee <br />dips 3o to the southeast, and strikes N35oW. This formation consists of <br />approximately 350 feet of interbedded sandstone, shale, carbonaceous shale, <br />and coal. Two coal seams appear to be the most continuous units in the <br />formation. The upper seam, which is the coal to be extracted, is about 4 feet <br />to 6 feet thick at the La Plata No. 1 mine site. <br />