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Histo <br />Extensive historic mining disturbances characterize the general area of the Southfield Mine. <br />In 1860 the first coal mine was opened in the northern portion of the Canon City Coal Field. <br />Production areas spread through the central area and into the southern portion of the <br />coalfield in the early 1900's. Over 177 abandoned mines with 600 acres of existing <br />associated surface disturbances have been identified by the Colorado Division of Minerals <br />and Geology's Inactive Mine Program. <br />Topo4raahy <br />The existing environment in the general area of the Southfield Mine is one of an arid, steppe <br />highland basin. The Canon City Coal Field/Basin lies in the transition zone between the <br />foothills of the Wet Mountains and the eastern Colorado plains, ranging from 5,500 to 8,000 <br />feet. The area can be characterized as a high plains mesa dipping gently to the east- <br />northeast. The mesa is dissected by several northeast trending ephemeral drainages. To <br />the west and southwest of the mesa are the Wet Mountains, where the drainages have their <br />headwaters. The Wet Mountain chain is fronted by a series of overthrust faults which results <br />in pre-Cambrian materials unconformably overlying overturned sedimentary units. <br />Erosion of the mountains has resulted in a pediment surface within the basin from 0 to 100 <br />feet thick. The action of several ephemeral and some perennial streams has cut through the <br />pediment surface, exposing the coal-bearing Vermejo Formation. This easily accessed coal <br />has been extensively mined since the turn of the century leaving many unreclaimed spoils <br />and waste piles. <br />Ge01ogV <br />The mine plan area is located along the east flank of the Wet Mountains adjacent to the axis <br />of the north plunging Chandler Syncline. The syncline parallels the trend of the Wet <br />Mountain Fault to the west. Strata on the northeast limb of the syncline dip gently to the west <br />at approximately 5 degrees. The southwest limb of the syncline dips very steeply and in <br />some cases strata on this limb are overturned. Dips in the southwest limb range from 45 <br />degrees NW to 85 degrees overturned. The Wet Mountain Fault is comprised of pre- <br />Cambrian granitic rocks uncomfortably overlying overturned sedimentary shales and <br />sandstone units of the Cretaceous age. Three units are of significance in the area -the <br />Pierre Shale, the Trinidad Sandstone and the Vermejo Formation (see Figure 3). <br />The Pierre Shale outcrops approximately 1.5 east of the mine area. The shale unit consists <br />of 3,900 feet of olive-gray clay and silt layers that contain bentonite and marine fossils. It is a <br />non-coal-bearing unit that exhibits very low hydraulic conductivity and thus is considered to <br />be a relatively impermeable unit. At the top of the Pierre is a sequence of thin, inter-bedded <br />sandstones and mudstones. <br />The Trinidad Sandstone, directly above the Pierre Shale, outcrops about 1.0 miles east of <br />the mine site and is composed of massive buff to yellow sandstones ranging from 40 to 90 <br />feet in thickness. The Trinidad Sandstone is indicative of a prodeltaic depositional <br />environment. <br />