Ohio River Bluffs

Natural History


Rooted in the Silurian.
To grasp the Bluffs region, imagine you are the Ohio River, heading west out of Pennsylvania and West Virginia. Sliding ever westward, you carve your wide floodplain through the sandstones and shales of the Appalachian foothills dropping down into older and older bedrock formations as you move across southeastern Ohio. These old bedrocks, and their associated acid soils, are actually the erosional residues of ancient and numerous uplifts of the Appalachian foothills over the mountain range’s incomprehensibly long history.

As you pass Portsmouth and the mouth of the Great Scioto, you approach a region known as Sandy Springs and the location of the Arc’s Rock Run Wilderness Preserve. Here a wide sinuous turn of the Ohio River marks the transition zone between the Devonian-age shales and sandstones and even older bedrocks – Silurian-aged limestones and dolomites which were formed by ancient seas 416 to 443 million years ago.

As you confront these more erosion-resistant limestone formations, your channel narrows. Your waters – now slowing down – dump large quantities of sand that characterize the Sandy Springs region we know today, with its sand dunes and vast sand flats. moving on through the Silurian-aged limestones and their associated neutral and alkaline soils, is where the wildflower magic happens.

For whatever reason, Silurian bedrock, compared to younger sandstones and shales of the Devonian and Permian ages, and compared to the older Ordovican limestones of Cincinnati, supports an astonishingly richer density of wildflowers. Consider that the exposed Silurian bedrocks and stream valleys in Ohio include such renowned wildflower sites as the Ohio River Bluffs, Whipple State Nature Preserve, the floral showcases of Adams County prairies, the Highlands Nature Sanctuary, and even north of the glacial advance, Glen Helen. Perhaps the Silurian bedrocks have the perfect concentration of minerals; perhaps there is something about the physical rock structures and how water permeates through them…We don’t know; but whatever the reason these bedrocks grow flowers with ease and abandon.

Ohio River Bluffs – one of a kind. The Silurian-aged bluffs along the Ohio River seem to want to bloom and they will overcome significant adversities to do so. Nevertheless, most of the Ohio River Bluffs’ floral displays have been destroyed by the agricultural clearing practices that began in earnest back in the 1800’s. Although most of the bluffs lining the river are now back in young forests of honey locust, black locust, redbud, cedar and hackberry, the understory has filled in with invasive bush honeysuckle. Native wildflowers are essentially absent. The small stretch of land between Gilkison Hollow and Owl Hollow Roads, where the Ohio River Bluffs Preserve is located, lays clam to being the most intact remnant of what was once an uninterrupted 25 mile long wildflower corridor on the Ohio River’s north shore.

Geological map of Ohio showing the area of Silurian bedrock along the Ohio River Corridor.
View of the Ohio River from the ridgetop at Ohio River Bluffs.