Information obtained from deep oil tests drilled in the past 5 years has disclosed that the Anadarko basin of western Oklahoma is separated from the central Oklahoma platform by a zone of buried large-scale faulting.

The major displacement in Cleveland and McClain counties is a fault zone, herein named the McClain County fault zone, which extends through the two counties from north to south, approximately bisecting them. The total throw of the zone reaches a maximum of more than 2,300 feet. The fault is considered to be a zone of shearing due to differential vertical uplifts between the positive central Oklahoma platform on the east, and the negative Anadarko basin on the west.

Numerous secondary faults are associated with the major fault zone.

Structural differentiation of the two structural provinces was established at least by late Ordovician time, and may possibly date from the pre-Cambrian. However, the major movements were concentrated in two periods of diastrophism in pre-Des Moines Pennsylvanian time.

Structural adjustments were in general continuous into Des Moines and later Pennsylvanian time; however, all faults pass upward into monoclinal folds in the lower part of the Deese group.