The area extends from the steep south flank to the gentle north flank of the Anadarko basin. The stratigraphy and tectonics are related to the orogeny of the Wichita Mountains. Normal marine beds were deposited from Arbuckle through Springer time. From Atoka through Wellington time the mountains were the source of much of the sediments. These sediments, predominantly arkosic, fingered into marine beds on the north. The arkosic material forms reservoir beds for most of the production in the area. The Pennsylvanian and Permian beds remain relatively constant in thickness in spite of the variability in the types of sediments. The Anadarko basin is an asymmetric syncline with the trough near the south edge of the basin. A structure of the Missouri series shows that Elk City f eld, the largest field in the area under discussion, is on a small closure in the trough. In this area the deepest part of the basin is in a syncline just west of Elk City field. Structure maps of younger beds show that the syncline gradually expanded until in Wellington time the field was incorporated within it.