Young County, located in the belt of Pennsylvanian and Permian formations of north-central Texas, is one of the important oil-bearing counties in the State. In 1930, a geologic map of the county was issued by the Bureau of Economic Geology of The University of Texas in cooperation with the American Association of Petroleum Geologists. In the southern part of the county, the formations were mapped at that time in considerable detail, but in the northern part, where the formations are difficult to follow owing to changes in facies, the mapping is less satisfactory. The principal purpose of this project was to add to the accuracy of geologic mapping in the county, and for this purpose, a limestone of the Harpersville formation was selected.

The detailed mapping of this limestone begins at a point approximately 3 miles southwest of Ft. Belknap near the northeast part of Texas Emigration and Land Company Survey, Block 3410, Fractional "B", and extends northward to New Castle, thence northeast along the outcrop of the Harpersville formation, passing about 4 miles south of Jean, thence in an easterly direction past Loving to the Jack County line.