The Big Sinking field is located high on the eastern side of the Cincinnati anticline and only 20 miles or so east of the outcrop of the Chattanooga shale and the Devonian limestone. The Silurian Lockport and Cayugan dolomites thin westward from about 600 feet in Magoffin County to extinction before the outcrop is reached, and the Devonian Hamilton limestone which is present at the outcrop thins eastward, is gone in the main part of the Big Sinking field, and if present at all west of Magoffin County is represented only by thin outliers. About 60 feet of strata are present between the Chattanooga shale and the green Silurian shales on the western edge of the field, perhaps a third of it being Hamilton and the rest Lockport, while 80-100 feet of strata occupy this position in the main part of the field, all of which is Lockport. Pre-Hamilton movements in the Cincinnati arch, with consequent stripping and leaching of the Silurian dolomites together with post-Hamilton erosion, were responsible for the creation of reservoir beds. This was not a case of oil accumulating on the side of a structure, but rather of the structure being responsible for the initial porosity and permeability of the formations lying unconformably below the Chattanooga shale. Silurian, and in some places even Ordovician, beds occupying this unconformable position have produced in various places around the Jessamine dome of the Cincinnati arch.

The wells are long-lived and respond readily to repressuring with air and gas, although acidization, perhaps due to the dolomitic character of the reservoir rock, has been less successful.