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• 2.04.6 <br />than contemporaneous basin subsidence (Weimer, 1976). <br />The Rollins Sandstone Member (Lee, 1912) of the Mesaverde <br />Formation represents the basal regression of the <br />Cretaceous Seaway, although Collins (1976) identified <br />seven cycles of marine-nonmarine deposition in the <br />Eastern Piceance Basin. The coal deposits of the area <br />were deposited as the complex relationships of deltaic, <br />fluvial, and barrier island facies were intermittently <br />modified by transgressive-regressive cycles of the <br />retreating Cretaceous shoreline. <br />The coal bearing member of the Mesaverde formation <br />locally contains up to nine mineable coal seams in the <br />North Fork Valley, named in ascending alphabetical order, <br />within the stratigraphic interval 500 to 600 ft. above <br />the Rollins Sandstone Member (Dunrud, 1976). Mines <br />recently operating in the various coal seams are as <br />follows: Somerset - C & B-2; Sanborn Creek - C 6 B-2; <br />Bowie No. 1 - D-2; Blue Ribbon and Hawks Nest - E-1; Bear <br />- C & B-2; Mountain Coal Company - F & B-2. Due to the <br />• depositional environment of the coal bearing member, <br />individual coal seams are not laterally continuous nor do <br />they maintain uniform thicknesses from differing <br />locations throughout the area. <br />The barren member of the Mesaverde formation is <br />lithologically similar to the coal bearing member with <br />the exception of virtually no mineable coal seams. In <br />the North Fork area, the barren member is <br />stratigraphically between the F coal seam and the Ohio <br />Creek conglomerate, and was estimated by Lee (1912) to be <br />1500 ft. thick. The scarcity of coal deposits within the <br />barren member probably represents progradation of <br />terrigenous, nonmarine sediments deposited in response to <br />the retreating shoreline. Hail (1972) reports maximum <br />thickness of the entire Mesaverde Formation to be about <br />2300 ft. <br />The Paleocene Ohio Creek Formation unconformably over <br />lies the Mesaverde formation. The Ohio Creek Formation <br />consists of light-gray, locally conglomeratic sandstone <br />. which ranges in thickness from locally C ft. to a maximum <br />P6PXIS 11PPLIGSION 2-04 - 12 - <br />