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thickness of the Upper Member of the Williams Fork formation on • Drawings 0-3-7, D-3-8 and D-3-9, the top of the Upper Sandstone would be approximately 2,000 feet lower on the west limb of the unnamed syncline (west of Sec. 30, T85, R90W) than at the site, (This assumes that the various Williams Fork formation members maintain about the same thickness from the mine site to the west edge of Drawing D-3-7), Therefore, the general westward ground water flow gradient would be maintained through the unnamed syncline and towards the axis of the Piceance Basin. The mineable coal occurs in the Mesa Verde group, which consists of the Iles and Williams Fork Formations and is approximately 5,000 feet thick, The Iles Formation overlies and intertongues with the Mancos Shale. In the Thompson Creek area, the uppermost and lowermost mem- bers of the Iles are the Rollins and Cozzette Sandstones, respec- tively, The middle member is composed of several hundred feet of shale, siltstone, and thin fine-grained sandstone. • The Williams Fork Formation, which overlies the Rollins Sandstone, contains all the mineable coals in the area (cross-section, A-A' Drawing D-3-8 ). The A-seam (Number 1 mine} overlies the Rollins Sandstone. The B-seam (inactive workings) is forty to sixty feet above the A-seam. Approximately 800 to 850 feet above the A-seam is the Upper Sunshine Seam (Number 3 mine) locally termed the Anderson seam, which is 65 to 70 feet above what is informally called the Upper Sandstone. The interval between the A Seam and the Upper Sunshine seam consists of shales, siltstone, sandy siltstones, sandstone len- ses, two massive Sandstones (Upper and Middle), lithologically similar to the Rollins Sandstone, and numerous thin coal beds. The sandstone lenses vary in thickness from several inches to ten feet. These lenses are lenticular and Taterally discontinuous, These lenses will not deplete flows from North Thompson Creek because the L 3-18