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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />0 Section 2 <br />Geologic and Hydrogeologic <br />Characteristics <br />2.1 Geologic Setting <br />2.1.1 Phisiography <br />The Sunday Mines Group is located within the Dolores River Basin, which is a part of <br />the Canyonlands division of the Colorado Plateaus physiographic province (Cater <br />1955). The affected areas of the mines are located on the south side of Big Gypsum <br />Valley, which is a broad valley extending west-northwest to the Dolores River. The <br />elevation of Big Gypsum Valley ranges from approximately 5,400 feet above mean sea <br />level (ft. amsl) near the Dolores River to over 5,800 ft. amsl on the eastern end of the <br />valley. Big Gypsum Valley is bounded on the north and south by steep slopes and <br />rocky outcrops. The ridge separating Big Gypsum Valley to the north from <br />Disappointment Valley to the south is approximately 6,400 ft. amsl elevation, with <br />vertical displacement from the valley floor to the ridge ranging from approximately <br />600 to 1,000 ft. <br />The underground portion of the mines extends from the affected areas towards the <br />south beneath the ridgeline separating Big Gypsum Valley from Disappointment <br />Valley. On the south side of the ridgeline, the underground workings lie beneath a <br />dip-slope that forms the north slope of Disappointment Valley. In this area, the <br />underground workings are approximately 600 feet below the surface. <br />The mines are located in an and environment, with sparse vegetation such as juniper, <br />pinon pine, cacti, and sage brush. Evaporation greatly exceeds precipitation in the <br />area, supporting the and environment. The only perennial surface water in the mine <br />area is the Dolores River, which receives the majority of its flow from snow melt and <br />precipitation occurring in mountainous areas surrounding the Dolores River Basin <br />(Weir et al. 1983). <br />2.1.2 Regional Stratigraphy <br />The regional stratigraphy is an important facet in developing an understanding of the <br />hydrogeologic characteristics of rock units in the area of the Sunday Mines Group. <br />Cater (1955) provides information regarding the regional stratigraphy, from which <br />this summary is derived. A geologic map of the region encompassing the Sunday <br />Mines group is included as Figure 2-1. <br />Rock units present in the vicinity of the Sunday Mines Group consist of Paleozoic <br />chemical sedimentary rocks overlain by a sequence of Mesozoic to Cenozoic clastic <br />sedimentary rocks. The rocks are locally overlain by a thin mantle of unconsolidated <br />cm 2-1 <br />7:\84986-Denison Mines\Task War 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Report\final sunday hydro reponVextTINAL Sunday Hydmgeology Repon.doc