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3 <br />5 <br />• ~ quartz sandstone 75 to 125 feet thick with dark gray, carbonaceous shale <br />locally present near the top of the unit. The Dakota Sandstone, also of <br />j early Cretaceous age, rests disconformably on the Purqatoire. It is a <br />massive quartz sandstone, often exhibiting prominent crossbedding, with <br />thin interbedded shale. Its thickness in the study area is estimated at <br />50 to 200 feet. The Graneros Shale rests conformably on the Dakota. It <br />is a dark gray to black shale with an estimated thickness of 200 feet. <br />The Cretaceous Greenhorn Limestone intertongues with the underlying Graneros <br />and consists of 20 to 30 feet of dark gray limestone with minor amounts of <br />interbedded shale. The Carlile Shale rests conformably on the Greenhorn <br />Limestone and is composed of approximately 200 feet of dark gray shale that <br />includes thin sandstones and limestones near the top. <br />The Niobrara formation is upper Cretaceous and commonly divided into <br />the Fart Hays Limestone and Smoky Hill Marl members. The Fort Hays Lime- <br />stone rests conformably on the Carlile and consists of 20 to 30 feet of <br />grdy limestone and shale. The Smoky Hill member probably exceeds 700 feet <br />in thickness and is composed of white to buff limestone and marl. <br />• <br />The Pierre Shale consists of a dark gray to black marine shale con- <br />taining several thin zones of limestone as well as an upper sequence of <br />gray to black shale interbedded with buff to gray sandstone. The Pierre <br />has an estimated thickness of 1800 to 1900 feet in the study area. <br />i <br />The Trinidad formation is a light gray to buff, slightly arkosic sand- <br />stone that locally contains thin interbeds of shale. The formation inter- <br />tongues and is gradational with the underlying Pierre Shale. This fine to <br />very fine sandstone is often a cliff-former and has a thickness of approxi- <br />mately 250 feet in the study area. <br />The Vermejo formation conformably overlies the Trinidad. Typically, <br />the Vermejo is made up of three lithologies, buff, gray to gray-green, <br />slightly arkosic sandstone; gray to black carbonaceous shale; and coal. <br />The Vermejo thickens rapidly west of Cokedale to over 300 feet. <br />• The Cretaceous-Paleocene, Raton formation constitutes the bedrock in <br />the study area. It rests unconformably on the Vermejo formation and <br />