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a <br />-23- <br />Basin. The sandstone is fine to very fine-grained, light gray to buff in <br />color, and is slightly arkosic. The Trinidad Sandstone reaches thicknesses of <br />250 feet in the general area and is a prominent cliff former. This sandstone <br />is separated from the coal seams by up to 900 feet of interbedded shales, <br />siltstones, and sandstones. <br />The Cretaceous Vermejo Formation conformably overlies the Cretaceous Trinidad <br />formation. Typically, the Vermejo Formation consists of three lithologies; <br />slightly arkosic sandstone, carbonaceous shale, and coal. The Vermejo rapidly <br />thickens west of the town of Cokedale to over 300 feet. <br />The Cretaceous to Paleocene aged Raton Formation is exposed at the surface in <br />the study area. It rests unconfornably above the Vernejo Formation and has a <br />total thickness of 1,200 to 1,600 ft. The base of the Raton Formation <br />consists of a buff to gray pebble conglomerate a few inches to several feet in <br />thickness. Most of the Raton Formation is composed of very fine to medium <br />grained sandstones including arkose, orthoquartzite and graywacke which are <br />interbedded with gray to dark gray siltstone and shale. The upper 100 to 200 <br />feet of the formation tends to contain coarse grained, arkosic sandstones and <br />light colored shales. <br />The coal seam which is being mined at the Maxwell Mine is the Maxwell seam, <br />and the Allen Mine is located in the Allen seam. Both the Allen and Maxwell <br />seams are located in the midd]e of the Raton Formation of Cretaceous age. The <br />Allen seam lies stratigraphically beneath the Maxwell coal seam. The seams <br />are separated by a thin interburden strata which varies in thickness from a <br />few feet in the Allen Mine to a few tens of feet in the Maxwell Mine. <br />The Paleocene Poison Canyon formation unconfonnabiy overlies the Raton <br />Formation and has a thickness of approximately 600 feet in the study area. It <br />occurs as small isolated outcrops. probably no thicker than 200 feet near the <br />study area. This formation consists of massive, very coarse arkosic <br />sandstone, pebble conglomerates, and thick shales. <br />Sills and dikes associated with Tertiary volcanism intrude the Vernejo and <br />Raton Formations and are visible in the Picketwire Valley. They range in <br />thickness from a few inches to greater than 20 feet and are primarily composed <br />of basalt. <br />Quaternary deposits consist primarily of river terrace and floodplain deposits <br />associated with the Purgatoire River and its tributaries. The study area <br />contains two levels of rock benches that formerly may have been referred to in <br />the literature as Beshoar and Barilla pediments. The applicant's consultant <br />has interpreted these as strath terraces with an alluvial veneer. These <br />strath terraces are located approximately 90 to 170 feet above the river in <br />the study area. They have been eroded from shale and siltstone containing <br />thin interbeds of fine to very fine, silty sandstone. The overlying alluvium <br />has a maximum thickness of approximately 35 feet and is composed of <br />predominantly silt and sand containing pebbles and occasional boulders. <br />