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- 12 - <br />A younger period of folding unrelated to salt techtonics occurred <br />in the late Cretaceous and early Tertiary. This period of folding <br />corresponds with the Laramide Orogeny in the Roddy Mountain Region to <br />the east. Rocks of the Morrison Formation and younger formations <br />which had not previously been folded were folded into broad anticlines <br />whose axes paralleled the major salt intrusions. At this time, the <br />salt intrusions were buried under several thousand feet of sedimentary <br />rock. <br />Cater (1970) believes that the collapse of the anticline crest <br />occurred in two stages, apparently widely separated in time. The <br />first stage of collapse, which involved the formation of grabens near <br />the crest of the anticlines, probably took place soon after the early <br />Tertiary folding. Grabens as much as several hundred . et deep <br />developed along the crest of the anticlines during this initial stage <br />of collapse. With the end of graben faulting, the salt anticlines <br />probably were structurally inactive for a long time. The second and <br />final stage of collapse occurred after the regional uplift of the <br />Colorado Plateau in the late Tertiary. Regional uplift caused <br />rejuvenation of streams in the area, and deep canyons were eroded into <br />the underlying sedimentary rock. Erosion along the Dolores River <br />eventually reached the salt core in the Paradox Valley anticline. At <br />this time, relatively rapid solution of salt started to take place. <br />The removal of salt and subsequent salt flowage is responsible for the <br />final collapse of the anticline's crest. During this period of <br />collapse, a complex system of northwest trending normal faults <br />developed along the Paradox Valley sides as shown on Figs. 4 and 5. <br />