Natural Athens Page

Geology of Athens County, Ohio

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This page was last revised on November 20, 2017.

Athens County is located in extreme southeastern Ohio, in the Appalachian Plateau area, which is the unglaciated band of lands that run across the southern and southeastern parts of the state. Unlike the flatter and smoother north, west and interior of Ohio, the unglaciated area is typified by hills and valleys, often with steep slopes, usually of 45-120 meters elevation change (150 to 400 feet).

Although this area may be unglaciated, it was heavily modified by the drainwaters from the glaciers. The Ohio River originally formed as a drainway near the southern boundary of the ice sheet, and rivers such as the Hocking in Athens County and the Scioto sixty miles west carried huge amounts of drainwater from these massive ice rivers. In fact, both the Hocking River and the Scioto River figured as part of the Teays River system, a large prehistoric river preceding the glaciers.

The rock strata underlying Athens are mostly sandstone and shale, with both large and small coal seams, "redbeds" (which are mostly shale), and some clay and some limestone. The sandstone often makes large outcrops and even small bluffs.

Probably the most commonly-noticed of these layers is the Connelsville Sandstone of the Conemaugh Group of the upper Pennsylvanian, which can readily be seen from Ohio Route 32/US Route 50 on the east side of Athens, particularly from the University Mall east to Stroud's Run dam, where the beds are the thickest known in the area. Through the county, the Connelsville Sandstone ranges from about twenty to about one hundred feet in thickness. This sandstone can also be readily seen along Long Run in the eastern county. To get to Long Run, turn off Stimson Avenue in Athens onto the US50/OH32 west ramp, then turn left on Rock Riffle Road just before the actual highway ramp. Take Rock Riffle Road to the stopsign at Long Run Road and turn right. After about 1/4 mile, you'll start noticing sandstone exposures along the creek, and they continue the length of the creek until it flows into Shade River. The creek dips at only a very slightly faster rate than the sandstone stratum.

Another sandstone that makes interesting outcrops is the Pomeroy Sandstone, but it's only prominent in the south-central county. There, it may reach thicknesses of up to fifty feet, but it's absent in much of the north county. This sandstone is stratigraphically above the Connelsville Sandstone, and is placed in the Monongahela Group of the uppermost Pennsylvanian.

There are also two sandstone strata that form significant outcrops in the western part of the county, both part of the mid-Pennsylvanian strata. In the extreme west of Athens County is the Lower Freeport Sandstone, ranging from eleven to sixty-six feet thick, and may be seen along the Hocking River just inside the county. Farther into the county is the Lower Mahoning Sandstone, ranging from five to over eighty feet thick, which makes some nice outcrops along the upper part of the bikeway.

Then, in the far-eastern part of Athens County, along the Hocking River, may be seen sandstone cliffs that are a combination of the Waynesburg, Mannington, and Washington Sandstones. These are of the lowermost Permian, and are among the youngest outcrops in the county.

All these strata are, on average, dipping down to the west, so that the oldest strata are exposed on the west side of the county and the youngest are exposed on the east. However, the slope of the strata is not great. This inclination is part of the eastern side of the Cincinnati Arch, a long anticlinal (upfolded) structure that has an axis approximately centered on Cincinnati, Ohio, and Lexington, Kentucky.

Because of the once-extensive coal underlying Athens County, coal-mining used to be an extensive industry here, both deep mining and strip mining. The County is still seriously suffering from the aftereffects of mining, with acid mine drainage from both kinds of sites, open mineshafts, and unreclaimed strip sites.

The most important coal seam in the county was the Middle Kittaning, also known as number six coal, of the middle-Pennsylvanian. This seam reached a thickness of some sixty-six feet in a large area of the county, though much less thick in most areas. The extensive mining of this seam, which is the principal seam that was involved in the mines along Sunday Creek, means that much of west-central Athens County is now sitting on an underground lake. The strata over this lake are gradually subsiding, forcing the acid water to the surface under pressure. Several artesian springs are now known, bleeding off this mine water.

Other coal seams of note are the Lower Kittaning (#5 coal), the Lower Freeport (#6a), and the Upper Freeport (#7), all in close proximity to the Middle Kittaning; all these seams are of the Allegheny Series of the Pennsylvanian. The Upper Freeport was formerly up to fifty-four feet thick in one area.

One other coal seam in Athens County was mined extensively: the Pittsburgh (#8) seam, of the Monongahela Series of the upper Pennsylvanian. In some places, this seam, too, reached sixty-six feet, but not nearly as extensively as the Middle Kittaning.

These thick areas in the seams were only in localized areas. In most areas, these seams were only a few feet thick.

Limestone in Athens County is usually present only in very thin strata or even only as nodules, but one seam is better developed than others. The Ames limestone has many outcroppings in central Athens County, and is even quarried somewhat, but is generally not very thick.

Another geographical note: the Hocking River once flowed through the Ohio University Campus in Athens. Some years ago, a new channel was dug on the far side of the flood plain, and the old channel was mostly filled in. The old channel does still carry a stream that drains stormwater. The Hockhocking Adena Bikeway follows the Hocking River from Athens to Robbins Crossing on the Hocking College campus outside of Nelsonville.

Geological Formations in Athens County

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