During Proterozoic time an east-west trough along the site of the present Uinta Moutains, received 20,000 or more feet of sediments, the source of which was in uplands east and north. These sediments, the Uinta Mountain group, are mainly sandstone and quartzite in the eastern part of the range. They form an homogenous shallow-rooted "pod" imbedded in the earth's crust which has tended to act as a unit in subsequent orogenic events.

No known important orogenic events disturbed the area from Cambrian through most of Mesozoic time. Commencing during the deposition of the Mesaverde formation in late Cretaceous time and continuing into Paleocene time, a low north-south uplift, the present Douglas Creek arch and south end of the Rock Springs uplift, was folded across the Uinta "pod." In Paleocene and early Eocene time the Uinta arch, roughly coincident with the "pod," was cross-folded normal to the

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older uplift. The "pod" was forced upward and outward over adjacent basins by depression of these basins located north, northeast, and south of the position of the "pod" in the earth's crust. There was an apparent combination of overthrusting of the mountains and underthrusting of the basins. Further, the "pod" was propelled east by compressive forces pushing from the orogenic belts of southeast Idaho and central Utah. Faulting along the flanks of the Uinta arch occurs in a zone of multiple ruptures and combines faults of normal, reverse, and overthrust types. Where the Uinta arch was folded across the older north-south trend, east-west cross-folds such as Rangely and Salt Wells anticlines resulted.

The Uinta Mountains were greatly reduced from middle Eocene through Miocene time, and the eastern end of the Uinta arch collapsed in late Miocene time into a complex regional graben.

The Rock Springs uplift and probably the Vermilion basin uplift are the result of a still younger episode of cross-folding and upwarping of Pliocene age which has possibly persisted into the Pleistocene in some minor movements.

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