All of the recognized tectonic features in the Four Corners region appear to be post-Humbug

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(Meramecian) in age and therefore had no influence on the earlier deposition of Mississippian sediments. The Mississippian system in this region is represented by the Madison, Leadville, Redwall, Humbug, and Manning Canyon formations. The Humbug and Manning Canyon formations are present only in the northwestern part of the area, due to erosion of the Humbug and the fact that the Manning Canyon was deposited only in the area of the Oquirrh basin of central Utah. At the close of Humbug time, strata of the Mississippian system formed the eastern shelf of the Cordilleran miogeosyncline, and was exposed over the positive area of the Southern Colorado Plateau, now known as the Paradox, Black Mesa, and San Juan basins.

The possibilities of finding oil and gas accumulations in the thick, commonly porous, carbonate sediments of Mississippian age are favorable along the Cordilleran shelf, or hinge area. Both stratigraphic and structural conditions are favorable in this area. The only Mississippian oil production in Utah is in the Paradox basin at the Big Flat unit, discovered in 1957 by the Pure Oil Company. The complex, subsurface, structural conditions of the Mississippian strata, in the Paradox basin, imply excellent possibilities for oil accumulation in structural traps.

It is concluded that there is a Cordilleran shelf or hinge area in south-central Utah and that the Mississippian formations can probably be correlated throughout the Four Corners region.

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