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• limitations as a result of their fine texture the soils of this unit are considered to be only moderately good <br />The soils of mapping unit number 31 have wide shrink/swell ratios, total potential extensibility of 40•inch <br />section ranges from about 2 to 6 inches. <br />In their natural state, these soils are not susceptible to much soil erosion unless native vegetation has been <br />destroyed or depleted. If cleared or disturbed they are very susceptible to wa[er erosion due to large <br />amounts of runoff, and moderately susceptible to wind erosion. <br />Minor evidence oC mass movement on some of the steeper slopes is observed. The soils of this unit have a <br />moderate to hieh potential for such movement and any practice involving the addition of large amounts of <br />++atcr on these soils will increase the susceptibility (or mass movement. <br />Chemical Properties and Natural Fertilirv -These soils are moderately weathered, maturely developed <br />having genetic horizons of silicate clay accumulations (B2t horizons) but normally lacking horizons of <br />secondary carbonate accumulation. The soil solum (A and B horizons) is neutral to mildly alkaline while <br />the C horizon is neutral to moderately alkaline and may contain some free carbonate. Under such <br />conditions [he cation exchange complex (portion of the soil having an ability to hold and exchange cations) <br />is normally base saturated with calcium being the predominant cation, but there is not enough tree calcium <br />and magnesium carbonate to seriously depress the availability o(other plant nutrients. Natural fertility <br />levels are high in the upper horizons oC the soil but gradually decrease with depth as organic content <br />decreases. No evidence of deficiencies of essential plant nutrients or of trace elements is observed. <br />Nitrogen supplies and availability are closely associated with the amount and decomposition of organic <br />• matter in the soil. Any practice that involves the loss of the organic rich upper soil horizons, more rapid <br />than normal decomposition of organic matter, or the prevention of an annual return of organic plant <br />remains could cause temporary nitrogen deficiencies. Supplemental fertilization of disturbed areas that are <br />ut be rcvcgetatcd wilt insure the best and most vigorous seedling gro+sahs. <br />MaPnine Unit Number X31 -This mapping unit has the same description as mapping unit number 31. <br />Classification of Maior Components -The components listed below comprise the major part of the <br />mapping unit: <br />A. Argic Crvoboroll (Chernozem). <br />1. Fine, montmorillonitic family. <br />(Gothic Series) <br />(Jem Series) <br />B. Argic Pachic Cryoboro]I (Chernozem). <br />1. Fine, montmorillonitic famih~. <br />(Cochetopa Series) <br />(Fulcher Series) <br />Extent and Maior Areas of Occurrence -Mapping unit number X31 has a large total acreage and occurs <br />throughout the mine area at elevations greater than 7,800 feet. Largest areas occur in the eastern, central, <br />and southern parts oC the mine area. <br />Characteristic Tonoeranhv -These soils occur on moderately to steeply sloping hill and valley type of <br />topography. T}pically they occupy side hill locations, buc unless bedrock occurs too close to the surface <br />. they occur on hill and ridge crests as well. Slopes range from about 3 percent to 60 percent. <br />sources (or seedbed materials <br />