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Portal Areas. In the canyon areas of the North Fork of the Gunnison <br />• River, the steep topography resembles in many places what could be <br />called a "natural highwall". The planned post-mining surface landscape <br />of the portal face-up for the Bear No. 1 and 2 Portal areas will blend <br />into and complement that surrounding topography; however, complete <br />backfilling of the face-up areas will not be undertaken. <br />The coal deposits along the North Fork of the Gunnison River lie in <br />Cretaceous rocks. As a result of regional uplift, the formations with <br />Cretaceous rocks are characterized by a natural bench with steep <br />topography along the North Fork of the Gunnison River. Hence, the coal <br />is exposed in a deep, essentially narrow canyon on the faces of what <br />Colorado characterizes as naturally occurring highwalls, formed over <br />centuries. Due to the rapidly increasing overburden thicknesses in this <br />area with these coal outcrops, most of the portal areas along the North <br />Fork of the Gunnison lie along the steep outcrop of the coal, with the <br />development of portals into the coal seam. <br />• The result of this method of extracting coal is the development of <br />benches, roads and other surface operation facilities in the canyons. <br />The No. 2 portal area has been constructed from the spoil removed from <br />the face-up area. The use of spoil in constructing a stable fill in the <br />portal area reduces the volume of material removed from the face. Hence <br />there has been less disturbance to the affected surface area. <br />Reclamation of the portal area to the elimination of the face-up or <br />highwall could be environmentally unsound and counterproductive to <br />reclamation requirements. <br />Complete elimination of a "highwall" in the canyon with average slopes <br />of 30° by backfilling to the angle of repose could create several <br />problems. Winter snow melt or intense summer thunder showers could <br />result in excessive erosion on the steep slopes. Moreover, the static <br />safety factor of 1.3 would be difficult to achieve without expensive <br />engineering construction. On the other hand, backfilling to a lesser <br />angle, such as 2 horizontal to 1 vertical or 3 horizontal to 1 vertical, <br />would be impractical because there would not be enough material from the <br />-24- <br />