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of the basin . The coal zones being mined dip to the west <br /> and southwest, beneath the divide of Huntsman Ridge . <br /> The average dip of the coal seams is 130 . <br /> Mine entries have followed the dip of the coal . Since the <br /> surface above the portals is very steep , depth has increased <br /> rapidly from the entry in the portal area to the present <br /> workings , which now occur at 3 , 000 ' in the B bed and 2 , 500 ' <br /> in the Middle bed . <br /> During future operations depth should remain <br /> fairly constant as the south and west slopes of the Hunts- <br /> man Ridge, which overlie the underground workings projected <br /> for the permit and mine life terms , roughly corresponds to <br /> the dip of the coal seams . <br /> • The outcropping strata of the Mesaverde <br /> formation occur as a rim around the erosional basin, which <br /> is floored by impermeable Mancos Shale . <br /> The lowest potential aquifer , and the base of <br /> the coal series , is the Rollins Sandstone, which overlies <br /> the Mancos Shale. <br /> The Rollins is 120 ' -140 ' thick and forms <br /> nearly vertical cliffs at outcrop . Grain is variable, with <br /> medium size predominant . The Rollins is the top of the Iles <br /> Formation, which is the lowest of the Mesaverde . <br /> Above the Rollins is the Coal Basin Coal <br /> Interval , which is 20 ' -30 ' thick, and contains the A and <br /> overlieing B bed coal seams . <br /> 29 <br />