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Soils of mapping unit number 20 are below normal for the area in general fertility, but this is due to their <br />• poor drainage and aeration rather than any limiting deficiency of available nutrients. Nitrogen levels arc <br />probahly low at the wetter seasons of the scar. <br />Manning Unit Number X25 - Moderately deep (20 to 40 inches to bedrock) and deep (more than 40 <br />inches to bedrock), dark colored, moderately coarse textured soils (less than 18 percent clay but finer than <br />loamy sands), having soil horizonation limited to dark surface horizons (A horizons) and occurring in parts <br />of the study area where [he mean summer soil temperature (June, July, and August mean temperature <br />measured at 20 inches) is colder than 59°F. <br />Classification of Maior Comnonents -The components listed below comprise the major part of the <br />mapping unit: <br />A. Typic Cryoborolls (Chcrnozem). <br />1. Coarse-loamy, mixed. <br />(Burnt Lake Series) <br />(Sawcrcck Series) <br />B. Pachic Cryoborolls (Chernozcm). <br />1. Coarse-loamy, mixed. <br />(Skyway Series) <br />Extent and Maior Areas of Occurrence - Mapping unit number X25 occurs in moderate acreage in the <br />study arcs and is found in greatest acreage in the eastern and central parts at elevations above 7,500 feet. <br />Characteristic Tonoeraphv -These soils occur in areas where the semi-consolidated sandstones of the <br />• underlying geologic beds occur close enough to the surface oC the ground to have been the major <br />contributors to the weathered earthy regolith. Consequently, the soils of mapping unit number X?5 <br />generally occur on gently sloping to moderately rolling ridges and mesa-like areas that arc underlain by <br />sandstone. Occasionally thec may occur on alluvial fans and alluvial-colluvial sideslopes below outcrops of <br />sandstone. Slopes range from about two to 25 percent in most areas. <br />Physical Properties -The soils of mapping unit number X25 are weakly developed below the surface <br />horizons (A horizons) and have only weak grades of natural structure. The unfavorable surface conditions <br />arc counteracted by the medium-coarse texture which insures good permcabilit}•. Any manipulation of <br />these soils will not greatly affect the quali[y of seedbed material. Compacted areas can usually be rectiLcd <br />by com~entional tillage methods. <br />Shrink~svell ratios of this unit arc very low. Total potential extensibility ranges from 0 to 0.8 inch for a <br />40-inch section. Thcrc is no evidence of mass movement and potential for this movemen[ is low. <br />Flat-topped mesa-like areas in the northeastern part oC the mine area have extensive areas of this soil <br />mapping unit. Shading patterns of aerial photographs result from the formation of dunes or drifts around <br />stands of oakbrush and juniper. This is considered the wind-eroded phase of mapping unit number X25. <br />Since the area is vulnerable to high winds, reclamation will be started promptly otter mining to provide <br />adequate protection. <br />Chemical Proocrties and Natural Fertility -These soils are weakly weathered and immature with no <br />genetic horizonation other than a dark surface horizon (A horizon). They are non-calcareous throughout <br />and neutral to mildly alkaline in reaction. Thus although the cation exchange complex (portion of the soil <br />• capable of holding and exchanging cations) is base saturated, with calcium as the principal cation, there is <br />no excess of calcium or magnesium as free carbonate to depress the availability of other essential plant <br />nutrients. <br />