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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />002538 <br /> <br />5 <br /> <br />All the Great Plains section was once covered by a veneer of <br />tertiary silt, sand, and gravel laid down by streams from <br />the mountains. This material has been stripped by erosion <br />from the piedmont and Raton sections, but several large <br />patches remain as remnants on the High Plains. These <br />remnants are composed mainly of the Ogallala Formation, but <br />locally include some younger deposits. <br /> <br />C. Soils <br /> <br />Along the Arkansas River and most of its tributaries the <br />lands occur as river bottom land, terraces, or benches and <br />alluvial fans. The uplands are residual soils derived from <br />shale, limestone, or sandstone, except in areas where <br />alluvial outwash overlies the residual soil. <br /> <br />Older soils which have remained in place long enough to <br />develop distinct layers that occur in many parts of the <br />area. They are characterized by a dark loamy topsoil and a <br />subsoil layer with a higher percentage of soluble minerals, <br />predominantly lime carbonate, and having a heavier texture <br />than that of the topsoil. The topsoil extends to depths of <br />10 to 18 inches, and the subsoil ranges in depths of 3 to 6 <br />feet. These older soils have developed principally on <br />gently sloped or nearly level areas where erosion has been <br />minor. <br /> <br />Young soils occur principally on slopes where the topsoil <br />has been removed by wind or water erosion almost as rapidly <br />as it was formed. Some of the young soils consist of dune <br />sand, silty loess material, and alluvial outwash. Those <br />derived from large stream deposits usually have a gravel <br />substratum which provides excellent natural drainage, and <br />those derived from small stream or wind deposits have no <br />gravel substratum. Lower floodplains have somewhat poorly <br />drained soils. <br /> <br />D. Crops <br /> <br />The daytime temperatures in the summer are high, while the <br />nights are cool. The cool nights are mainly due to <br />altitude, low humidity, and moderate winds. The winters are <br />generally moderate. The entire study area falls in the 180- <br />to 190-day average duration frost-free season (28 degrees <br />F.) and 160- to 170-days average duration frost-free season <br />(32 degrees F.). <br /> <br />A wide variety of crops are grown in the study area. The <br />area from Pueblo to La Junta has fair to good water quality. <br />Here, corn and alfalfa are the principal crops, along with <br />