Figure 12.— Natural revegetation on old spoils near the Seneca mines in Colorado. The spoil piles were flattened on the top 

 and then airseeded with grass. The slopes are from 35° to 40°. The pits at the end of mining trenches are filled with water. 

 They contain small amounts of bullrushes and provide waterfowl habitats. The coal slack (foreground) remains essentially 

 unvegetated. Perennial cover is sparse in contrast to the naturally vegetated slopes in the background, but some shrubs, 

 mainly big sagebrush, have naturally invaded the spoil. Some exotic trees and shrubs were planted on these spoils, and the 

 survivors are doing well. October 1978. 



(Thornburg and Fuchs, 1978, p. 414). Some in- 

 vestigators (U.S. Geological Survey and Montana 

 Department of State Lands, 1979, p. 11-28-29) 

 think that the high levels of precipitation in the 

 last 10 years in Montana represent the high part 

 of a general 21 -year cycle which is expected to 

 decline. 



LANDFORM 



The reshaped form of the mined land surface 

 strongly influences the potential for reclamation 

 success. In the past, this surface encompassed 

 the nearly vertical cliffs, or highv\/alls, which 

 marked the end of the mine pit area (figs. 10 and 

 22) and mine pits or other depressions that 

 would be perennially or seasonally flooded 

 (fig. 12). Most of the other disturbed ground was 



composed of piles of spoil that formed coalesc- 

 ing hills and ridges having slopes at the angle of 

 repose of loose material (figs. 3, 7, and 10). 



Erosion is greater on steep slopes and on long 

 slopes. On these slopes, seeds or seedlings, 

 even if they can be established, are likely to be 

 washed away or buried by eroding material. 

 Steep slopes are dry even if they are composed 

 of porous material because the rainfall runs off 

 rapidly. Although annuals and sparse clumps of 

 grasses may be observed, stabilizing vegetation 

 is difficult to establish either artificially or natu- 

 rally on steep slopes (figs. 7 and 23), and they 

 may remain almost bare after 40 years. An 

 almost impermeable surface is formed when 

 slopes are composed of clay, particularly swell- 

 ing clay. At dry, windy sites, extensive flat areas 

 can also be ultimately unproductive because 

 wind erosion may create shallow depressions in 



27 



