Roadside Geology of Scioto County, Ohio: A Traveler’s Guide

Nestled in the foothills of the Appalachian Plateau, Scioto County offers more than just scenic beauty—it’s a living laboratory of Earth’s dynamic history. From ancient oceans to Ice Age floods, the rocks and landscapes here tell a fascinating geologic tale. If you're a geology buff, nature lover, or curious traveler, this guide is your roadmap to exploring some of Ohio’s most compelling natural features.

A Geologic Map of Ohio (ODNR)

A Journey Through Deep Time: Scioto County’s Geologic Story

The bedrock of Scioto County is a record of over 450 million years of geological evolution. Starting in the Ordovician Period, shallow inland seas deposited layers of limestone, sandstone, and shale, forming the foundation of the region. These layers are rich in marine fossils—remnants of a time when southern Ohio lay near the equator beneath warm, tropical waters.

During the late Paleozoic Era, mountain-building events like the Alleghenian orogeny uplifted and folded these sediments. Fast forward to the Pleistocene Ice Age, when massive glaciers swept across Ohio, reshaping ancient rivers and leaving behind a patchwork of moraines, outwash plains, and glacial lake deposits. One such glacial lake—Glacial Lake Tight—once covered a vast part of the county, dramatically altering its topography.

Top Geological Destinations (Now with Deeper Science!)

1. Shawnee State Forest – Ohio’s Little Smokies

Shawnee State Forest sits atop Mississippian-aged rocks, including the Borden Formation and Maxville Limestone (~330 million years old). These formations represent deltaic and shallow marine environments, with occasional limestone lenses formed in clear, warm seas. You can also find evidence of ancient karst features like small caves and sinkholes in the Maxville Limestone, which was dissolved by groundwater after deposition.

🧠 Did you know? The Borden Formation’s greenish-gray shale contains fossils of crinoids and brachiopods, animals that once lived on the seafloor.

View point from the gazebo at Shawnee State Park Lodge and Conference Center. Notice the layer of fog atop the mountains in the distance.

2. Scioto River Valley

This wide, fertile valley was shaped during the Wisconsinan glaciation (~20,000 years ago). The current Scioto River follows a reorganized path after the Teays River—a preglacial river system—was buried by glacial till. Beneath the valley lies up to 400 feet of unconsolidated sediment, including sand, gravel, and clay, making it one of the best spots in Ohio to study glacial and post-glacial hydrology.

🧠 Did you know? Boreholes in the valley show that ancient river gravels lie directly atop bedrock, under thick glacial lake deposits left by Lake Tight.

Kayak launch point on the Scioto River near Lucasville, OH.

3. Raven Rock Natural Arch

This arch, formed in the Pennsylvanian-age Conemaugh Group, was shaped by differential erosion. Harder layers of sandstone resisted erosion, while underlying shale and siltstone were worn away, leaving behind the arch. These rocks were laid down about 310 million years ago in a fluvial system of swamps, rivers, and floodplains, occasionally punctuated by marine incursions.

🧠 Fun fact: The sandstones here often exhibit cross-bedding and iron oxide staining, indicators of ancient river channels and oxidation processes.

Raven Rock. Raven Rock State Nature Preserve, West Portsmouth, OH

4. McDermott Quarry & Berea Sandstone Outcrops

Just west of McDermott, along the railroad tracks, you’ll find outcrops of the Berea Sandstone, a late Devonian to early Mississippian unit (~360 million years old). These sandstones were deposited in a tidal delta environment, and many outcrops exhibit soft-sediment deformation, where wet sand was slumped or folded before fully lithifying.

🧠 Look closely! You might spot ripple marks, planar bedding, and ball-and-pillow structures—all signs of ancient sediment dynamics.

Cook's Photography, Portsmouth, Ohio, “Taylor Stone Stockyard McDermott, Ohio,” Scioto County Public Library Local History Digital Collection, accessed June 4, 2025, https://www.sciotolibrary.org/history/items/show/5362.

5. Glacial Features & Glacial Lake Tight Deposits

Lake Tight was formed when glaciers dammed the ancient Teays River, flooding valleys and depositing varved clays, silts, and fine sands in the still water. These sediments are still visible in stream cuts and roadside exposures. As the glacier retreated, it left behind kames (gravel mounds), terraces, and outwash plains, especially visible north of Portsmouth.

🧠 Geology in action: The modern drainage system of Scioto County is a product of this glacial interference, showing how climate change shaped local hydrology.

Figure 1—A GIS model showing Lake Tight in blue. Islands that would have existed above the lake’s estimated water level are shown in brown, and yellow areas denote exposures of paleomagnetically reversed sediments. The red line shows the Teays River’s path prior to glacial damming. The green line shows the limit of glaciation, marking the southernmost glacial advancement and where the natural impoundment of the Teays River occurred. Image reprinted from “A New Map of Pleistocene Proglacial Lake Tight Based on GIS Modeling and Analysis,” by James Erjavec, 2018, Ohio Journal of Science, Vol. 118, pg. 61.

6. Route 823 – Portsmouth Bypass Corridor

This modern highway slices through sedimentary layers from the Mississippian and Pennsylvanian periods, exposing excellent roadcut geology. You’ll see shale, siltstone, sandstone, and even thin coal seams. The layers often contain marine fossils such as brachiopods, bryozoans, and crinoid columnals.

🧠 Field tip: These roadcuts are textbook examples of cyclothems—repeating sequences of marine and non-marine sedimentation, common in the Pennsylvanian.

An aerial view of Route 823 Bypass overlooking the Ohio River in the background. In order to make the road, they had to blast their way through the hills and mountains. The geologic formations can be easily seen as you travel along the roadway.

7. Route 52 – Ohio River Scenic Byway

Running parallel to the Ohio River, Route 52 shows off river terraces, loess deposits, and glacial outwash. The terraces represent multiple stages of river downcutting following glacial retreat. Loess, a fine windblown silt, caps many of the bluffs and is a direct indicator of Pleistocene climate conditions.

🧠 At the bluffs: Look for exposed stratified sands and gravels below loess layers—each represents a past episode of high river flow or glacial meltwater surges.

🗺️ Suggested Roadside Stops

• Shawnee State Forest Trails – See Mississippian formations and karst features.

• Scioto River Overlooks – Study valley fill and glacial outwash.

• Raven Rock Trailhead – Observe sandstone arch formation processes.

• McDermott Quarry Site – View tidal and deltaic bedding structures.

• Route 823 Roadcuts – Examine Paleozoic fossil-rich strata.

• Route 52 Pull-Offs – Investigate terrace stratigraphy and loess caps.

Top Hiking Trails & Sites to Explore Geology in Scioto County

1. Tremper Mound and Earthworks

• Location: Near Portsmouth, along the Scioto River

• Highlights: Tremper Mound is a significant Hopewell culture site, built around 100 BCE–500 CE. While primarily archaeological, its setting provides an excellent example of the Scioto River Valley’s alluvial and glacial geology. The mound sits on fertile glacial outwash plains, which made it a prime location for early human settlement.

• Geological Significance:

  • Positioned on an elevated terrace above the floodplain.

  • Near exposures of Quaternary sediments and buried glacial channels.

  • Provides views of pre-glacial valley alignment along the former Teays River drainage system.

• Access: While there is no formal hiking trail, you can walk around the mound site and along the riverbank to observe its geologic setting.

• More Information: Arc of Appalachia – Tremper Mound

Tremper Mound. Photo by Brian Prose

2. Shawnee State Forest

• Location: Western Part of Scioto County

• Highlights: Known as “Ohio’s Little Smokies,” this vast forest lies on Mississippian-age sandstone and shale, forming steep ridges and deep hollows characteristic of the unglaciated Appalachian Plateau.

• Recommended Trails:

  • Shawnee Backpacking Trail (35 miles) – A multiday trek through varied terrain, ideal for serious hikers and geology enthusiasts.

  • Lampblack Trail & Day Hikes – Shorter options through ridge-top and valley exposures, often cutting through Berea Sandstone outcrops.

• Features: Fossiliferous layers, iron ore seams, ancient weathering profiles.

• More Information: ODNR Shawnee State Forest or ODNR Shawnee State Park

3. Raven Rock State Nature Preserve

• Location: West Portsmouth, above the Ohio River

• Highlights: A dramatic overlook from a natural sandstone arch, formed through weathering and stream erosion of the Upper Mississippian sandstone.

• Trail: Short but steep hike (permit required) to the top of the cliff, offering spectacular views of the Ohio River Valley—a landscape shaped by glacial meltwater and ancient river courses.

• More Information: Raven Rock Preserve Info

4. Ohio Hanging Rock Preserve

• Location: Near Wheelersburg, OH

• Highlights: Unique sandstone cliffs and overhangs, ideal for studying erosion features, jointing, and rock shelter formation.

• Geological Features: Part of the Pottsville Group, the Hanging Rock area displays sedimentary sequences with cross-bedded sandstones, once part of ancient river deltas.

• Access: Maintained trails through the preserve by the Arc of Appalachia nonprofit.

• More Information: Arc of Appalachia – Ohio Hanging Rock

Hiking through Ohio Hanging Rock Preserve reveals these giant sandstone cliffs and overhangs.

🧭 Tips for Roadside & Trailside Geology Exploration

• Bring binoculars and a notebook to record your observations.

• Use topographic maps or GPS apps with geology layers like Rockd or USGS Topo Maps.

• Check Permits: Raven Rock and some preserves require advance permission.

• Layer Up: Many trails go from valley to ridge, so temperatures can vary.

• Watch for Fossils: Particularly in the shale layers of Shawnee Forest and near stream beds.

• Stay safe: Use designated trails, and do not collect fossils or disturb natural outcrops unless permitted.

  
  

Final Thoughts

Scioto County offers more than just scenic drives—it’s a living textbook of geological processes, from ancient seas to glacial floods and Appalachian uplift. Whether you’re hiking to an overlook or cruising along Route 52, the land tells a story carved in stone.