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82 SOIL FORDIING FPCTORS • Natural soils farm under the influence of five soil-forming factors: parent materials, organisms, climate, relief, arxi time. Differ- entiation of natural soils into different taxononuc groupings therefore result fran differences in one or more soil-forming factors. In this survey area, it appears that parent material is fairly constant and that vegetation, climate, relief, and soil age vary gradually over the landscape. Soils within the nP+*n;t area have developed primarily in inter- bedded sc~diltientary strata and locally transported valley-filling sideslope deposits. Generally, the soils overlie soft interbedded shale and sandstone formations at depths ranging from two (2) to eighteen (18) inches. Depth to this paralithic contact increases on less steep landscapes and concave north facing sideslopes. Here, soils are more developed (older) and less eroded. The vegetation type is generally upland sage. Thinner less developed • (younger) soils with drier micro-climates are found on the very steep southwest facing sideslopes that are adjacent to the dis- sected drainages. The vegetation type is predaninantly Juniper. A detailed discussion of local climate and topography for the Nucla Mine is presented in the soil survey text, Tab 9. muv cnrr.c Peabody Coal Ca~any, in conjunction with the U.S. Department of Agriculttse, Soil Conservation Service, Norwood, Colorado conducted a reconnaissance of Nucla Dune surface soils in 1975. This soil survey, colleted on aerial photos flown July 22, 1975, included the east pit area. The survey showed soil 9904, Persayo-Shavano clay loams occurring on sloping to moderately steep ridgetops and steep north facing sideslopes. Soil 18, Torriorthent-Rock Outcrop Complex (Rough Broken Land) occupies steep to very steep stoney sarrlstone ridges, bluffs, and sharp rolling lands. U