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• consists of interbedded sandstone and shale. The character <br />of the unit is similar to the lower members, except that the <br />sandstones are more lenticular and the shales are esentially <br />barren of coal. <br />In the study area the upper portion of the Mesaverde <br />Formation has been eroded; the bedrock units are capped by <br />colluvium and limited alluvial deposits. Thickness of <br />overburden above the D-seam is shown on Plate 7 for the area <br />of study. The local colluvium is often characterized by the <br />presence of basaltic material. The Mesaverde Formation is <br />underlain by the Mancos Shale, which outcrops below the <br />southern boundary of the lease area. This unit is far below <br />any layers disturbed by coal mining. <br />Bedding in the mine area dips from 2 to 5 degrees in an <br />approximately north-northeast direction. Structure contours <br />for the top of the D-seam are shown on Plate 2. CWI has <br />documented the faults frequently encountered in the mine, <br />indicating a system of faults which trend generally east- <br />northeast and northwest. Lineament trends on air photos <br />documented by CWI exhibit an east - northeast and northwest <br />pattern also (Plate 2). A major northwest trending fault was <br />encountered in mining which showed a 47 foot displacement of <br />the D-seam. Shear planes between the D-seam and the shale <br />• roof are also frequently encountered. <br />Point load and unconfined compressive strength tests <br />were performed on material Erom the Upper and Lower Coal <br />Members. Unconfined compressive strengths range from <br />approximately 5,000 to 29,000 psi for the sandstones, and <br />4,300 psi for carbonaceous siltstone to 16,000 psi for iron- <br />cemented siltstone. The results of unconfined compressive <br />strength and point load testing are present in the appendix. <br />2.3 HYDROLOGY <br />The lease area is drained to North Fork Gunnison River <br />by Roatcap Creek, Stevens Gulch, Terror Creek and several <br />minor, unnamed streams. Only Terror Creek is a perennial <br />stream; others are ephemeral or intermittent. The surface <br />water regime is dealt with in detail in Section 3.2 <br />Ground water is limited to Quaternary deposits and .to <br />the Mesaverde Formation; from the Quaternary deposits only <br />alluvial sediments at one vocation in Stevens Gulch are an <br />important aquifer that has been used by CWI ns a water <br />supply sour^_e. Another potential source of ground water is <br />• <br />-8- <br />