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C. Ustollic Camborthids (Regosol or Brown Soil). • 1. Fine, montmorillonitic, mesic family. (Razor Series) (Cadoma Series) D. Usteric Camborthids (Regosol or Brown Soil). 1. Fine, montmorillonitic, mesic (amily. (Heldt Series) E. Vertic Camborthids (Regosol or Grumosol). 1. Fine, montmorillonitic, mesic family. (Colons Series) Borollic Camborthids (Regosol or Brown Soil). 1. Fine, montmorillonitic family. (Bundyman Series) (Kemmerer Series) Extcni and r`gajor Areas of Occurrence - Mapping unit number 5 occurs in moderate acreage in the mine arcs. The largest acreage occurs in the southwestern part of the area along, and just to the west of Minnesota Creek. Although some areas were mapped within the National Forest boundary, most oC the unit occurs in that part of the survey obtained from the Soil Conservation Service survey of the Paonia area. Characteristic Toroeranhv - Soils of this mapping unit occur on two different geomorphic surfaces. Where the majority of sedimentary bedrocks are fine textured they frequently occur in alluvial fans and valley filling sideslopes below exposures of sedimentary rocks. They also occur in landscapes where the • soils are mostly residual or only very locally transported. In the former landscape they occupy gently to moderately sloping tans that are often dissected by steep- ++•allcd gullies and drainage channels. In the second type of landscape they occupy undulating to steeply sloping interlluvial hills and ridges separated by moderately sloping allu+9a1 valleys. Slopes range from about five to 40 percent with the deeper soils occurring on the more gentle slopes. Physical Properties -The soils of mapping unit number 5 are young soils and lack well-developed soil structure. They contain a high proportion of silt and clay which, in conjunction with their lack of good soil structure, makes careful soil management a requisite in any operation requiring good permeability and aeration after disturbance. They are very susceptible to packing if traversed by heave machinery and are easily irreversibly paddled if handled when too wet. These soils have high shrink/swell potentials with coefficients of linear extensibility ranging from 0.0? to 0.19 and a 40-inch section ranging from about one to four inches. \Vhen wet they are very slippery and stick~•. These soils arc considered to have poor workability (where workability is the abilin• to be disturbed or transported without serious physical change). They can be worked over only a narrow range oC soil moisture conditions. Without good natural soil structure to assist in main[enance of desirable physical characteristics they tend to (arm large and extremely hard irregular clods that are difficult to work into good seedbeds with conventional machinery and practices. In their native condition these soils arc subject to moderate overflow due to runoff and arc moderately susceptible to water erosion, especially gullying and tilling. Under native cover they are no[ susceptible to • accelerated wind erosion unless badly overgrazed.