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eroded surface of the aquifer and therefore, has been contoured to the same extent as the <br />bottom of the aquifer. <br />For the figures discussed below, the top and bottom structural contours and the control <br />and database picks will be provided in shapefile format, and the net sand thicknesses <br />will be provided in ArcGrid format to the CWCB as part of this TM. <br />3.1 Dawson Aquifer <br />The footprint of the Dawson Aquifer, including divided and undivided regions, <br />encompasses approximately 1,345 square miles (mil) and is located primarily within <br />Douglas, Elbert, and El Paso Counties. Figure 4 shows the top elevation contours of the <br />Dawson Aquifer. A total of 59 database picks and additional control picks were used to <br />contour the Dawson Aquifer top (Table 1). The elevation of the top picks range from <br />approximately 5,500 feet to over 7,500 feet. The highest elevations occur in the southern <br />portion of the basin, just east of Palmer Lake. There are not many picks for the top, <br />because in most areas the top of the Dawson Aquifer is equivalent to ground surface, <br />which is evident in the contours presented on Figure 4. The exception to this is where <br />the Dawson is covered by the Castle Rock conglomerate or unconsolidated valley-fill <br />deposits. <br />Figure 5 presents the bottom elevation of the Upper Dawson Aquifer, which is also the <br />top of the Dawson Aquifer confining unit. The footprint of the Upper Dawson bottom, <br />located within the divided region of the Dawson Aquifer, is approximately 660 mil and <br />is located within Douglas and Elbert Counties. There were 269 database picks with one <br />additional control pick used to contour the Upper Dawson bottom (Table 1). Bottom <br />elevations range from 5,700 to 6,700 feet, with the highest elevations occurring in the <br />southern region of the basin. Several picks are plotted just outside the aquifer extent in <br />Townships 8 and 9S and Range 67W, which may indicate that the confining unit <br />between the Upper and Lower Dawson Aquifers extends beyond the outline shown. A <br />comparison of the top and bottom elevations of the Upper Dawson Aquifer within the <br />divided portion of this aquifer indicates that its thickness extends up to 500 feet. <br />Figure 6 presents contours for the top elevation of the Lower Dawson Aquifer, which is <br />also the bottom of the Dawson Aquifer confining unit. There were 331 database picks <br />and one control pick used to contour this surface (Table 1). Elevations of the top of the <br />Lower Dawson range from 5,600 feet in the northern region to over 6,600 feet in the <br />southern region. Several picks are plotted just outside the aquifer extent in Townships 8 <br />and 9S and Range 67W, which may indicate that the confining unit between the Upper <br />and Lower Dawson Aquifers extends beyond the outline shown. A comparison of the <br />top and bottom elevations of the confining unit indicates that its thickness extends up to <br />200 feet. A comparison of the top of the Lower Dawson and bottom of the Dawson <br />elevations indicates that its thickness extends up to 400 feet. <br />Figure 7 presents contours for the bottom elevation of the Dawson Aquifer. There were <br />641 database picks with additional control picks used to contour this surface (Table 1). <br />Bottom elevations of the Dawson Aquifer range from 5,400 to 6,800 feet, with the highest <br />elevations occurring in the southern portion of the basin. The majority of the <br />SPDSS Phase 2 Task 42.2 TM -Final 14 <br />2/13/06 <br />