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Hydrogeological Evaluation of Van 4 Mine <br />Geologic and Hydrogeologic Characteristics <br />0 Section 2 <br />Geologic and Hydrogeologic <br />Characteristics <br />2.1 Geologic Setting <br />2.1.1 Physiography <br />The Van 4 Mine is located in the Paradox Basin within the Colorado Plateau <br />physiographic province of Colorado, Utah, Arizona and New Mexico. The Paradox <br />Basin includes a portion of western Colorado and eastern Utah that includes Paradox <br />Valley and portions of the Dolores River Basin. Land surface elevation within the <br />Paradox Basin ranges from approximately 5,000 to 14,000 ft. amsl. The area is <br />characterized by variable physiography ranging from high desert to evergreen forest <br />and, at elevations above tree-line, alpine tundra. The Paradox Basin is characterized <br />by a high degree of structural relief often expressed as intermountain valleys and <br />plateaus with deeply-incised canyons cut into gently dipping sedimentary rock. <br />Benches and mesas are commonly found where resistant rock outcrops and erosion <br />has removed softer strata. (Weir et al. 1983). <br />The Van 4 mine is located in the Paradox Valley area on Monogram mesa, which is a <br />mesa located on the south side of Paradox Valley. Monogram Mesa has elevations of <br />• up to 7000 ft. amsl, and is displaced approximately 1400 ft. above the floor of Paradox <br />Valley. A steep slope is present between Paradox Valley and Monogram Mesa, which <br />is controlled by a major fault zone associated with the Pardox Valley Anticline. The <br />surface topography of Monogram Mesa slopes gently southwest towards a major <br />canyon called Bull Canyon. Bull Canyon flows into the Dolores River at a location <br />approximately 7 miles southwest of the Van 4 Mine. <br />2.1.2 Regional Stratigraphy <br />The regional stratigraphy is an important facet in developing an understanding of the <br />hydrogeologic framework of the Van 4 Mine. Cater (1955) provides information <br />regarding the regional stratigraphy, from which this summary is derived. A geologic <br />map of the region encompassing the Van 4 Mine is included as Figure 2-1. Rock units <br />present in the vicinity of the Van 4 mine consist of a sequence of Mesozoic to <br />Cenozoic sedimentary rocks. A thin mantle of unconsolidated Quaternary sediments <br />locally overlies the sedimentary rocks. <br />The sedimentary rocks contain various portions of sandstone, siltstone, shale, <br />conglomerate and local limestone, and range in age from Triassic to Cretaceous. The <br />sequence includes the following formations: <br /> <br />2-1 <br />draft final van 4 hydreg.clogy report.doc