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~• The Round Bottom basin, however, is a geographically extensive area. <br />According to the "Geology .of Ptoffat County, Colorado" (A. Miller, 1977) <br />the area between the axis of the Williams Fork Anticline and the Round <br />Bottom Syncline encompasses 14 square miles. The other limb accounts for <br />roughly three times the area. <br />Hydrologic Setting <br />The major units of hydrologic interest in the extension area are the <br />so-called Middle Sandstone, and the overlying Twentymile Sandstone. The <br />Twentymile Sandstone outcrops in the immediate vicinity, and creates a dip <br />slope topography. According to the drilling in the area, the Twentymile <br />• is unsaturated in the area. The Middle Sandstone is comprised of two to <br />C . three distinct lithologic units. Cross Section E-E' (Plate III-le) is <br />presented to show the structural and stratigraphic relationships. This <br />plate is confidential. <br />The three units are labeled the A, B, and C units, each representing <br />the deposits of separate regressive events. Although well developed <br />locally, the A unit is not widely recognized as an aquifer aver most of <br />the property. The B unit is even more areally limited, as one can see, <br />the gradation from marginal marine to continental deposits in the <br />relatively small area illustrated in this cross section. The C unit is <br />probably the mdst widely distributed member of the t•liddle Sandstone, and <br />as such, is the unit commonly monitored at the Eagle Fiine Complex. To the <br />• Northwest, and particularly on the "Bell Rock Tract" there is a fourth <br />sandstone in the series that probably represents the last regression of <br />the tliddie Sea. <br />