The Fox structure is an irregular domal anticline of low relief separated from the elongated northwest-southwest trending Graham anticline by a deep seated fault.

The gently folded Permian rocks unconformably overlie a highly faulted, folded, and truncated Pennsylvanian section.

API gravities of the oil produced increase with depth, ranging from 19 degrees at 75 meters to more than 40 degrees at 1030 meters. As of 1955 there were 742 producing wells.