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Salt- and gypsum-bearing sediments exceeding 10,000 feet in thickness are known in the Jurassic of central Utah and in the Pennsylvanian of eastern Utah and western Colorado. Similar structures, both large and small scale, appear in association with deformed salt-bearing beds in the two areas.
Evidence seems to indicate that structural evolution of the two areas followed essentially similar lines: (1) gradual upthrust of elongate masses of plastic sediment perhaps under compressional forces or perhaps under purely geostatic pressure, (2) stagnation or cessation of upward movement allowing uniform sedimentation across sites of former acute deformation, (3) collapse by solution with subsequent erosion forming normal faults, synclinal grabens, graben valleys, and perhaps, with local oversteepening, actual "gravity thrusts."
Caution is suggested in interpreting strong local structures of the sort found in these areas as evidence for orogenic activity.
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