A system of faults in southwestern Arkansas extends from the faulted Irma field in southern Nevada County, Arkansas, southwestward across Lafayette and Miller counties, nearly to the Texas state line. The grabens range in width from 2 to 3 miles and have a total length of 50 miles. This series of faults follows the strike of the Wilcox-Claiborne contact along the northern part of the alignment, but along the southwestern part the line of weakness advances down-dip until this faulted zone lies entirely within the area of the Claiborne outcrop.

The Falcon fault, outlined at the surface by the division of non-marine beds of the Wilcox and Claiborne formations into lithologic units on the basis of their typical ferruginous concretions, was later verified by geological test wells. From the Lewisville fault in Lafayette County, westward, the faulted zone is obscured by a mantle of alluvium and Quaternary sand and gravel and was outlined by shallow geological test wells.

Thirty-seven geological test wells were drilled along the faulted zone, disclosing three closures against the southern boundary of the grabens. One deep test on the Falcon closure tested all of the sands of the Upper Cretaceous and 1,300 feet of the Lower Cretaceous. This well, which was favorably located with reference to the geological structure, yielded only showings of oil and gas. As the result of this work it is felt that although seemingly the most promising areas along this fault zone have been carefully tested, there still remains some possibility of opening deep commercial pools between the Irma field and the Texas state line.