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Doc Date:12/11/2001 II I I II I IIIII IIII III <br />~ S~E - 2.1 GEOLOGY <br />2.1.1 GENERAL GEOLOGIC SETTING <br />The Edna Mine is located in a sequence of deformed sedimentary rocks between <br />The Park Range and the Axial Basin Anticline. The sedimentary rocks are of Upper <br />Cretaceous and Tertiary age, and are situated in the southeastern part of the <br />Washakie-Sand Wash Structural Basin on the eastern limb of the Twentymile Park <br />Syncline as shown on Exhibits 2.1-I (1:24000) and 2.1-2 (1:4800). <br />Rock units exposed in the vicinity of the Twentymile Park Syncline include the <br />Mancos Shale, Iles Formation, Williams Fork Formation, Lewis Shale, Browns Park <br />Formation and volcanics of Tertiary age (Exhibit 2.1-3). <br />Mancos Shale <br />The Mancos Shale rests conformably upon the Dakota Sandstone and conformably <br />underlies the Iles Formation. It is nearly 5,000 feet thick and consists mainly of <br />~~_ <br />medium to dark grey shales that contain occasional thin, bedded, fossiliferous, <br />calcareous sandstone. Fossils that are prominently represented in the Mancos include <br />clams, worm tubes and shark teeth. The marine formation weathers and erodes to <br />form rough rolling topography. The Mancos Shale (Km on Exhibit 2.1-I) occurs near <br />the eastern edge of the study area. <br />Iles Formation <br />The Mesaverde Group conformably overlies the Mancos and consists of the Iles <br />and Williams Fork formations, both of which are also Upper Cretaceous in age. The <br />Iles Formation (Ki on Exhibits 2.1-I and 2.1-2) is approximately 1,500 feet thick and <br />is composed of sandstone, shale and coal. The base of the Iles is generally defined <br />by the Tow Creek Sandstone Member, a light brown, fine grain, well-sorted <br />sandstone. However, along Oak Creek this unit either thins out or contains <br />considerably more silt and clay, for iT is far less prominent than elsewhere in the <br />region. The Mancos-Iles contact in this area is identified as the base of the first <br />sandstone above the predominance of shale. The Iles contains several massive <br />sandstones that are similar lithologically to the Tow Creek. They include the Double <br />Ledge Sandstone, the Oak Creek Sandstone that has the Pinnacle Cools associated <br />2.1-I <br />