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edge, there is a small channel located where the Beebe Draw Alluvium converges with the <br />South Platte Alluvium. <br />Cross section B-B', shown in Figure 13, is located near Kersey at the Kersey gaging station. This <br />cross section depicts more of an incised paleochannel than A-A' but still lacks the steep banks <br />seen in downstream cross sections. The bedrock surface is nearly flat along the northern edge, <br />rolls into the valley bottom, which extends for over a mile, and then rises steeply in the south. <br />Cross section C-C', shown in Figure 14, is located just upstream of Fort Morgan. The deepest <br />part of the alluvial paleochannel is approximately one-half mile wide and then broadens out <br />and extends for a total width of nearly 7 miles. On the left (north) side of the cross section, the <br />bedrock surface at an elevation of approximately 4,175 feet and between distance markers 1 and <br />2 shows a smaller channel eroded into the bedrock surface. This likely represented the location <br />of the ancestral South Platte River at an earlier time. <br />Cross section D-D', shown in Figure 15, is located downstream of Brush near the Balzac stream <br />gage. It shows a narrow, incised valley bottom approximately 1 mile wide and deepens to 3,900 <br />feet. Above an elevation of approximately 4,050 feet, but still almost 70 feet below the water <br />table surface, on the south side of the valley bottom, the slope of the bedrock surface is nearly <br />flat and extends out approximately 3 miles. This could represent the bottom elevation of the <br />river channel at the end of a particular cycle of glaciation, when the river meandered into and <br />eroded away the bedrock in the area of this bench. On the north side, the slope on the bedrock <br />surface is much steeper and only extends approximately 1 mile from the valley bottom. The <br />water table in this region is at approximately 4,100 feet. <br />Cross section E - E', shown in Figure 16, is located near the Town of Sterling. Compared to <br />Cross section D-D', which is approximately 25 miles to the southwest, the valley bottom shows <br />gentler side slopes. The elevation of the valley bottom has decreased by 200 feet from Cross <br />section D-D' to approximately 3,700 feet, and the water table has also decreased by <br />approximately 200 feet to 3,900 feet. <br />Cross section F-F', shown in Figure 17, is located between the Towns of Sterling and Julesburg <br />in northeastern Logan County. At this location, the valley bottom is wider than at upstream <br />locations, and contains a deep channel underneath a ground surface high. The slope of the <br />bedrock surface on the south side of the valley bottom is much steeper than at Cross section D- <br />D', whereas the slope on the north side is similar to Cross section E-E'. As with Cross section D- <br />D', the bedrock surface is asymmetric, but the steeper side is on the south valley wall. The <br />valley bottom and water table elevations again decreased by approximately 200 feet from Cross <br />section E-E'. <br />4.0 Summary and Conclusions <br />CDM has completed SPDSS Tasks 31 and 42, the Phase 1, 2, and 3 collection, analysis, and <br />mapping of aquifer configuration data for the South Platte Alluvium Region. This report <br />examines the sources and types of available alluvial aquifer configuration data during Phases 1, <br />2, and 3 of the SPDSS. It describes the processing of the data used to generate a grid of the <br />bottom of the alluvium, a grid of the water level surface, a grid of the saturated thickness, and a <br />SPDSS Phase 3 Task 42.3 TM -Final 14 <br />11/30/2006 <br />