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2.04.6 <br />. Dakota Sandstone U er Cretaceous) <br />The Dakota Sandstone (approx. 100 feet thick) of late <br />Cretaceous age is a coastal-plain deposit laid down in front of <br />the advancing Mancos sea. The Dakota consists of conglomeratic <br />channel sandstone, dark-grey carbonaceous shale, coal, and, in <br />places, a marine sand stone at the top. Some of the sandstone is <br />fine grained and thin bedded and some is course grained and cross <br />bedded. Occurring scattered through the sandstones are irregu- <br />lar, discontinuous beds and lenses of conglomerate containing <br />chert, quartz and limestone pebbles. Interfingered with the <br />sandstone beds are thin-bedded gray and black carbonaceous shales <br />with coal seams as much as 6 feet thick. The Dakota does not <br />generally contain mineable coal; however, one strip mine near <br />Nucla provided coal for the nearby power plant. There also are <br />coal prospects in the Cortez area. The Dakota is preserved on the <br />mesas in the permit area but the top has been removed by erosion. <br />Quaternary age deposits <br />The Quaternary age depositions consist of seolian mate- <br />rial, alluvium and talus. This material is predominantly eolian <br />but some is alluvial having been reworked by water and intermixed <br />by sheet wash. The greatest observed thickness in some of the <br />dry washes in the area is about 10 feet. The surface deposits <br />• range up to about 6 feet in thickness. Talus slopes along the <br />canyon sides are comprised of colluvium and dry stream beds are <br />composed of alluvium with some gravel deposits. The alluvium is <br />principally light brown to light gray sand, silt and clay with <br />discontinuous stratified layers of gravel. The gravel consists <br />primarily of pebbles of sandstone, limestone, chert, quartz and <br />some shale. The colluvium and block rubble are comprised of <br />sandstone, conglomerate and shale derived from the overlying <br />younger sedimentary beds cut by the canyons. The deposited <br />material in these canyons varies in depths up to about 30 feet. <br />Coal Structure <br />Structure contours have been drawn for the coal horizon <br />in the permit area. These are presented on the Top of Seam <br />Contour Map, Drawing No. 107. From these it can be seen that the <br />strike of the coal horizon lies in an east west direction, and <br />the coal seam dips 2% to 3% to the north. <br />No major faults have been <br />area and present experience along <br />indicates that no faults of large <br />adjacent area. <br />• 2.04-6 <br />recognized within the permit <br />with drill hole information <br />displacement exist in the <br />May 1991 <br />