The Cushing oil and gas field has produced nearly 300,000,000 barrels of oil since the completion of the discovery well in 1912. This amount is exceeded only by two other continuous fields in the United States. Accumulation of oil in the field is due to the presence of an anticline 20 miles in length. The producing area comprises 34 square miles. The average yield per acre to January 1, 1928, was 12,993 barrels. Previous publications relative to the Cushing field have not discussed in detail the unconformable relation between the Pennsylvanian strata and underlying rocks. At the Dropright dome, the Bartlesville sand (lower Pennsylvanian) rests on the Arbuckle limestone (lower Ordovician). This unconformable condition is present but less pronounced throughout the entire fi ld. The pre-Pennsylvanian rocks on the east limb dip at a rate of 15°. The west flank dips at a rate of less than 2°. Several erosion cycles have affected the rocks in the Cushing district. The fold was probably present as an anticline at the end of Arbuckle time. Local history of movement cannot be traced during Ordovician, Silurian, Devonian, or Mississippian time. In early Pennsylvanian time the Cushing anticline was again uplifted. Subsequent erosion of the newly formed anticline resulted in the typical concentric distribution of outcrops about the anticlinal axis. The base-leveled anticline was later covered by the advancing early Pennsylvanian sea. Gentle uplifting occurred contemporaneously with the deposition of the Pennsylvanian rocks. The predominant west dip of surface beds throughout the region suggests a westward tilting of the Cushing anticline at some time after the deposition of the Pawhuska formation, outcroppings of which occur in the Cushing field.