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of the Morrison Formation. A thin mantle of eolian silts and sand <br />commonly occurs on the valley floor and on the mesa tops. <br />Structure: The salt anticline region of the Colorado Plateau is a <br />structurally complex area. The majority of the structural complexity <br />is the result of collapse of the salt anticline crests in Tertiary <br />time. The Paradox Valley is aligned along the axis of one of the <br />major salt anticlines in the region. The general structure of the <br />valley and in the vicinity of the JD-5 lease is shown on Figs 4 <br />and 5. <br />Prior to crestal collapse in Tertiary time, the structure of the <br />Paradox Valley salt anticline was relatively simple. Initial folding <br />started with diapiric salt intrusion in late Pennsylvanian time during <br />the deposition of the Limestone member of the Hermosa Formation. <br />Folding and some associated faulting of the anticline are the result <br />of the squeezing of salt from the adjacent Dry Creek and Nucla <br />synclines to the southwest and northeast. Initial salt intrusion was <br />probably related to displacements on the basement fault which <br />underlies the Paradox Valley, Cater (1970). Thinning and truncation <br />of Post - Paradox and Pre-Morrison Formation along the flanks of the <br />anticline indicate that the salt structure was periodically developing <br />during this time interval. At the start of Morrison time, most of the <br />salt was apparently squeezed from the adjacent synclines, and salt <br />intrusions essentially stopped. This is indicated by the thicknesses <br />of the Morrison and younger formations. The thickness of the Morrison <br />Formation and overlying the Burro Canyon Formation and Dakota <br />Sandstone, is little affected in the vicinities of the anticline. <br />