Figure 13.— Aerial photograph showing the hummocky surface created by rounding off tops of spoils at an older part of the 

 Seneca nnine in Colorado. The graded highwall forms the right side of the draw. These grass-covered stable surfaces con- 

 trast sharply with the darker surrounding mountain brushland. October 1978. 



which salts accumulate as a result of the evapo- 

 ration of water. 



Aspect, the direction that a slope faces rela- 

 tive to the Sun, also affects plant growth. Even 

 where temperatures are generally cool, average 

 precipitation high, and evaporation low, as in the 

 northwest Colorado coalfields, old south- and 

 'west-facing spoil slopes remain bare if they are 

 composed of very coarsely textured materials 

 (Berg, 1975, p. 81). North- and east-facing slopes 

 are cooler, more moist, and therefore are usually 

 easier to revegetate (Jonescu, 1974). South- and 

 west-facing slopes are hotter, drier, and gener- 

 ally more difficult to revegetate (frontispiece A). 

 Seed mixes tailored according to slope aspect 

 have not been widely used in reclamation. 



As discussed under the section "Climate," 

 most surface manipulations that help catch and 

 conserve moisture also reduce erosion. Regula- 

 tions now require that the new surface be gen- 

 erally similar to the premining surface and that 

 the slope of the highwalls be reduced. 



OVERBURDEN 



The chemical and physical characteristics of 

 the geologic materials lying above the coal, 

 called overburden, or between coalbeds where 

 more than one bed is to be mined, called inter- 

 burden, are significant parameters in reclama- 

 tion success. These characteristics are espe- 

 cially true where spoils comprise all or part of 

 the new growth media, because they control in- 

 ternal drainage and contribute harmful or plant- 

 growth-limiting materials. In general, the clayey 

 materials present the greatest problems in west- 

 ern reclamation because they are slow to absorb 

 moisture and often have high salt content; these 

 properties are responsible for poor revegetation 

 success at many sites. Sodium-rich expanding 

 clays are particularly adverse for seed germina- 

 tion and growth (fig. 24). Where both sandy and 

 clayey materials are present in the overburden, 

 some successful intermixing can be done in the 

 stripping process (Dollhopf, 1979) to reduce the 



28 



