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Studies by Schultz and others (1980) also showed elevated sulfur and <br />trace mineral concentrations in studies done of the Upper Cretaceous <br />Pierre shale and equivalent formations. The sediment source areas for <br />these formations was to the west. The watershed area is far from the <br />source area, so sediments are almost exclusively fine - grained marine <br />shale and muddy limestone. As the amount of clays increase with <br />distance from the sediment source area, so does the amount of organic <br />carbon. Adsorption from seawater and concentration by organic matter <br />have increased the concentrations of arsenic, chromium, copper, <br />selenium, uranium, and other trace minerals in the formations present <br />in the watershed area. <br />1 � Check in Reference Section for Geology Reports. <br />Soils <br />The soils in the watershed are mainly of the Rocky Ford series. Soils <br />of the Rocky Ford series are moderately shallow to deep, calcareous, <br />and medium textured. They are on terraces of the Arkansas River and <br />its major tributaries. <br />All of these soils are irrigated with water from the Fort Lyon Canal <br />Company and are silted. Generally, the surface layer is heavily silted <br />because the muddy water used to irrigate this soil has deposited silt <br />and clay. In many places where water tends to pond at the lower end of <br />a field, the soil is more deeply silted than it is in the other areas. <br />In many of the steeper areas, the surface layer is coarser than it is <br />in nearly level areas. In some of these areas, plowing has mixed part <br />of the lighter colored subsoil with the surface layer. In places land <br />leveling or deep tillage has greatly altered or affected some of the <br />soils. <br />The surface layer of these soils is dark grayish -brown clay loam and is <br />10 to 15 inches thick. It is hard when dry and firm when moist. The <br />Subsoil, or horizon underlying the silted surface layer, is brown silt <br />loam that is slightly hard when dry and friable when moist. This silt <br />loam grades to lighter colored silt loam. These soils are calcareous <br />throughout. <br />Crop yields are high, but some of these soils need more careful <br />management than others because they are shallow over limestone or sand <br />and gravel. The main problems are managing irrigation water, <br />maintaining fertility, and controlling erosion on the steeper slopes. <br />O] <br />i <br />117 <br />0 <br />n <br />0 <br />1 <br />