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U <br />rocks. The sedimentary rocks in the northwestern portion of the <br />basin, in the vicinity of the JD-5 lease, range in age from Cambrian <br />to Cretaceous. Formations present in this area are shown on the <br />stratigraphic column Fig. 3. <br />From Cambrian through Mississipian time, the area was covered by <br />marine waters. About 1,000 feet of sandstone, limestone and dolomite <br />were deposited in Southwestern Colorado at this time. A short period <br />of emergence occurred in early Pennsylvanian time. During this <br />period, a karst topography and a thin regolith developed at the ground <br />surface, Hite and Lohman (1973). <br />Rapid subsidence of the Paradox Basin started in early <br />Pennsylvaaian time and was accompanied by uplift in the marginal area, <br />particularly in the Uncompahgre Uplift which bordered the basin on the <br />northeast. The present day Uncompahgre Plateau is located near the <br />center of this Pennsylvanian Uplift. During this period of <br />subsidence, a thick section of evaporite and clastic sediments, the <br />Paradox member of the Hermosa Formation, was deposited in the basin. <br />The Paradox member probably attained a maximum thickness of about <br />6,000 feet. Post - depositional flowage has markedly increased the <br />thickness of the Paradox member in the cores of the salt anticlines. <br />Thicknesses up to 15,000 feet have been encountered in the core of the <br />Paradox Valley anticline. The Paradox member exhibits a cyclic <br />pattern of chemical and clastic sedimentation. Hite and Lohman (1973) <br />have identified 29 evaporite cycles. Lithologies comprising beds of a <br />cycle are anhydrite, dolomite, black shale and halite. Potash salts <br />are associated with some of the halite beds. Individual lithologic <br />