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developed soils has~ng mature soil horizonation including horizons of silicate clay accumulation (B2t <br />• horizons) and horizons of secondary carbonate accumulation occurring in parts of the study area where the <br />mean summer soil temperature (June, July, and August mean temperature measured at 20 inches) is 59°F <br />or warmer. <br />Classification of Maior Comnonents <br />mapping unit: <br />The components listed below comprise the major part of the <br />A. Ustollic Haplargids (Brown Soils). <br />1. Fine-loamy, mixed, mesic. <br />(Cushman Series) <br />(Fon Collins Series) <br />(Pueslcy Series) <br />(Olney Series) <br />B. Borollic Haplargids (Brown Soils). <br />1. Fine-loamy, mixed. <br />(Cushool Series) <br />(Forelle Series) <br />(Alcova Series) <br />(Satanka Series) <br />(Fluetsch Series) <br />Extent and 1,Qaior Areas of Occurrence - Mapping unit number 16 occurs in small acreage in the West <br />Elk study area and is found principally on the terraces and valley (illine sideslopes east of Minnesota <br />Crcck and north of its east fork. <br />• Characicristic Tonoeranhv - Soils o(this mapping unit occupy gently to moderately sloping stream <br />terraces and the lower ends of alluvial fans and valley filling sideslopes. Slopes are uniform, ranging from <br />about two percent to ten percent. <br />Physical Properties The soils of mapping unit number 16 are mature soils with distinct horizonation <br />and well developed, stable natural soil structure. This soil structure is essential to the movement of air <br />and water through the soil and to the penetration of plant roots. With proper management it can be <br />preserved and at least partially recreated even if the soil is disturbed. The soils of mapping unit number <br />I6 arc good sources for seedbed material. <br />The soils of this mapping unit are medium to moderately fine textured and are subject to packing if <br />continuously traversed by heavy machinery. They can be handled over a moderate range of soil moisture <br />without serious loss of favorable properties; however, they can be irreversibly paddled if handled when too <br />wet. Thus while physical damage can be done by improper handling methods, the dancer is not as erect as <br />in finer textured soils or soils with little or no structure. <br />These soils have moderate shrink/swell ratios. Coefficients of linear extensibiliry range Crom 0.2 to 0.05 <br />and total potential expansion of a AO inch thickness ranges from 0.8 to 2.0 inches. <br />Normally, the soils of this unit are not subject to serious hood hazards although a few areas immediately <br />adjacent to permanent streams may Oood occasionally. In their natural state they are not susceptible to <br />much accclcratcd erosion unless native vegetative cover has been destroyed or seriously depleted. When <br />disturbed and cleared they are moderately susceptible to both wind and water erosion and should be <br />manaecd with appropriate control measures. <br />• No tendency toward mass movement is noted within areas mapped as unit number 16 and the potential for <br />such movement is low. <br />