During Pennsylvanian and Permian time, the Colorado Plateau area underwent the most active period of tectonic activity of the Paleozoic and Mesozoic eras. A continuous parageosynclinal seaway extended from the Oquirrh sag of east-central Utah southeast into central New Mexico. Greatest subsidence occurred in the Paradox basin, an asymmetrical half-graben, where in excess of 6,500 feet of marine and restricted marine sediments accumulated during Pennsylvanian time. Peripheral to this seaway were the orogenic Uncompahgre-San Luis uplift, the epeirogenic Kaibab-Defiance-Zuni uplift, and the epeirogenic Emery uplift. Along the Uncompahgre and Kaibab-Zuni structural trends, tectonism originated earliest in their southeastern segments and progressed northwest.

Two elements, the Defiance uplift and a southeastward projecting spur of the Emery uplift, bear major economic implications. The Defiance uplift, a structural subsidiary of the Kaibab-Zuni trend, projected north into the southern Paradox basin. It was active in pre-Pennsylvanian time and affected depositional patterns of marine sediments from Morrow? to Wolfcamp in age. Major hydrocarbon production in the Four Corners area bears a close relation to this element geographically and geologically. Because of Kaibab-Zuni tectonism, only the northern third of the Black Mesa basin appears favorable for hydrocarbon accumulations in Pennsylvanian rocks.

The Emery spur projected into the northwestern Paradox basin and affected depositional patterns of sediments from Des Moines into Wolfcamp time. Geologic conditions east of the Emery uplift, and adjacent to its southeastern spur, appear more favorable for hydrocarbon accumulations in Pennsylvanian sediments than those present in the producing part of the Four Corners area. Recent discoveries on the western Paradox Basin shelf prove the presence of oil in marine sandstone stringers and reef-type build-ups within the Hermosa formation. Regional lithologic analyses indicate that this trend may be extended from the southern Emery flank to the northern Kaibab flank.

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