Laserfiche WebLink
II.B GEOLOGY <br />11.8.1 General Stratiaraphy The rocks exposed throughout the Deserado Mine Permit area <br />are contained within the Mesaverde Group of Upper Cretaceous age. These sedimentary beds are <br />well exposed as a southwest facing escarpment along the flank of the Rangely anticline and along the <br />course of Scullion Gulch and its tributaries. <br />Gaskill and Hom in an unpublished report on the northeast Rangely coal field describe the Mesaverde <br />as "largely composed of yellowish to very light gray, massive, thin bedded and flaggy, angular to <br />subangular, very fine to fine grained quartz sandstone, interbedded with sandy gray shale, siltstone <br />and mudstone, carbonaceous shale, coal, and occasional thin often concretionary lenses of limey <br />sandstone and sandy limestones." They state that it appears to be divisible into at least two units. <br />The Mesaverde Group in the mine permit area has not been previously subdivided on a formational <br />basis. Throughout much of northwestern Colorado, the Mesaverde has been divided into the basal <br />Iles Formation, and the overlying Williams Fork Formation, with the contact lying atop the Trout Creek <br />Sandstone Member of the Iles Formation. The Trout Creek Sandstone has been tentatively identified <br />east of the mine permit area near Elk Springs. Mapping by J.L. Cullins (1971) within the Rangely <br />Quadrangle, identifies the Trout Creek Sandstone equivalent east of Douglas Creek about three miles <br />• southeast of Rangely and seven miles south of the mine permit area. <br />It is generally recognized that the principal coal zone within the Mesaverde Group in the permit area <br />occurs near the base of the Williams Fork Formation and just above the Trout Creek Sandstone. <br />Furthermore, coals within the Iles Formation are known to be thin and laterally discontinuous. The <br />lithology of the Iles Formation is dominated by laterally continuous sandstone and shales. <br />Based on this information and on data gathered during field mapping and exploratory drilling, the <br />strata exposed in the mine permit area have been subdivided into three zones. In ascending order <br />the three zones are the Iles Formation, the Lower Williams Fork Formation, and the Upper Williams <br />Fork Formation. <br />Within the permit area the strata beneath the principal coal zone display a greater abundance of <br />coarser grained sediments (i.e., sandstones) than does the overlying coal-bearing interval. It also <br />contains few, if any, significantly thick or continuous coal seams. Therefore, this sequence of rocks <br />is considered the Iles Formation equivalent. Much of the upper Iles is exposed in the steep slope <br />along the north bank of the White River immediately west of where County Road 65 bridges the river. <br /> <br />(Permit Renewal #3 1/99) II.B-1 <br />