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<br />Studies by Schultz and others (1980) also showed elevated sulfur and trace mineral <br />concentrations in studies done of the Upper Cretaceous Pierre shale and equivalent <br />formations. The sediment source areas for these formations was to the west. The <br />watershed area is far from the source area, so sediments in this area are almost <br />exclusively fine-grained marine shale and muddy limestone. As the amount of clays <br />increase with distance from seawater, and organic matter increasesthe concentrations <br />of arsenic, chromium, copper, selenium, uranium, and other trace minerals in the <br />formations in the watershed area. <br /> <br />Quaternary deposits overlay the bedrock throughout much of the watershed area. <br />These deposits generally consist of unconsolidated clay, silt, sand, gravel, and <br />sometimes cobbles and boulders. <br /> <br />Groundwater in the watershed is in both confined and unconfined water table <br />conditions. The youngest confined aquifer in the area is the Lower Cretaceous <br />Dakota sandstone, which is not exposed in the watershed. The flow in the Dakota <br />sandstone is toward the northeast and the recharge area of the Dakota formation is <br />the outcrop area to the southwest of the watershed. Activities and surficial <br />contamination sources in the watershed generally have little if any effect on water <br />quality in the confined aquifers. <br /> <br />Unconfined conditions in the watershed occur primarily in the alluvial and terrace <br />deposits along the Arkansas River and its tributaries. Groundwater flow in the <br />unconfined aquifer is generally toward the river. Recharge to the unconfined aquifer is <br />from precipitation, irrigation, and leakage from canals, ditches, and drains in the <br />watershed. It is this unconfined aquifer that is the most susceptible to contamination <br />from septic systems, feed lots, fertilizer, and pesticides. <br /> <br />Soils <br /> <br />The soils in the watershed are mainly of the Rocky Ford- Numa-Kornman Association. <br />The soils of the Rocky Ford series are deep, nearly level, well drained, loamy soils. <br />They are on terraces of the Arkansas River and its major tributaries. <br /> <br />All of these soils are irrigated with water from the Highline, Otero, Catlin, Rocky Ford, <br />and Oxford Canals. Generally, the surface layer is heavily silted because the muddy <br />water used to irrigate this soil carries silt and clay. In many places where water tends <br />to pond at the lower end of a field, the soil is more deeply silted than it is in the other <br />areas. In many of the steeper areas, the surface layer is coarser than it is in nearly <br />level areas. In some of these areas, plowing has mixed part of the lighter colored <br />subsoil with the surface layer. In places land leveling or deep tillage has greatly <br />altered or affected some of the soils. <br /> <br />The fertile surface layer of these soils is grayish-brown silty clay loam and is about 18 <br />inches thick. It is hard when dry and friable when moist. The subsoil, or the horizon <br />underlying the silted surface layer, is brown silt loam that is easily penetrated by plant <br />roots, air, and water. This silt loam grades to lighter colored silt loam at a depth of 3 <br />inches and is coarse textured. Many of the soils have some salts. <br /> <br />11 <br />