Summer 1996

It's those d----d redbeds. A redcoat, General Edward Braddock, may well have been the first to utter these words. As the first road builder across the Appalachian Plateau, his wagons may have slipped, slid, and become mired in the plastic mud of wet redbeds that are so conspicuous in the Plateau.

Distribution of landslide-prone redbeds in Ohio.

Red rock is well known and renowned in the American West through the images portrayed in films set in the midst of towering red cliffs and dramatic still photographs of scenes in Arizona, Utah, and neighboring states. But red-colored sedimentary rocks--known to geologists as redbeds--are found not just in our West, where they measure hundreds to thousands of feet in thickness, but throughout the world, including eastern Ohio and adjacent parts of the Appalachian Plateau. However, instead of majestic sandstone cliffs, the redbeds of the Appalachian Plateau are soft shales that weather rapidly and slip, slide, and flow to form gentle contours that are quickly grassed over. They are, in fact, barely, if at all, noticed by the casual observer, and outcrops are difficult to find, even by an experienced geologist who is looking for them.

Ohio's redbeds and those throughout the Appalachian Plateau are sedimentary rocks that consist primarily of clay-sized particles but contain some silt and sand. They are commonly calcareous and may be associated with limestone. Redbeds may lack any order or structure such as smooth layering or bedding planes and may appear as a simple, poorly bedded mass of rock.

Redbeds interbedded with light-colored nonmarine limestone of the Monongahela Group (Pennsylvanian) along I-77, near Macksburg, Washington County.

The thickness of individual Ohio redbeds ranges from a few to tens of feet, and they are commonly sandwiched between drab-looking shale and sandstone. As the term "redbed" suggests, they are typically brick red but vary in color, and have been described by Ohio geologists as pink to red, chocolate red, reddish brown, maroon to purple, and purplish red. They may also be variegated or mottled gray and red, and locally may even be partly green. They are particularly common in Ohio in the upper half of Pennsylvanian-age rocks (Conemaugh Group and Monongahela Group) and in the Dunkard Group of Early Permian age.

The red coloring is the result of oxidation of iron-bearing minerals to iron oxide--rust. Concentrations of as little as 4 percent iron minerals (iron oxide) can effectively stain the rock red. Historically, two major hypotheses have been developed to explain the red color of these beds. One theory holds that the red staining was acquired in a tropical or semitropical environment and the red materials were then transported to an area of deposition. The opposing hypothesis contends that the red color of the sediments was obtained after deposition, through weathering, and that many redbeds represent ancient soils, known as paleosols. Recent studies suggest that Appalachian Plateau redbeds represent delta-plain sediments that have been subject to seasonal wetting/drying cycles.

This landslide in redbeds in the Conemaugh Group (Pennsylvanian) in 1986 destroyed the westbound lanes of I-70 near New Concord, Guernsey County. Repairs took 30 days and cost more than $600,000.

Redbeds are a significant economic detriment throughout the Appalachian Plateau because of their propensity for forming landslides, although they may be useful in the future as landfill bedliners. These soft rocks composed mostly of clay deteriorate quickly when wet, becoming a sticky, gooey, plastic mud that can mire anything from beasts to vehicles of all kinds. Many years ago, while doing field work for the Survey, I found a man mired hip deep in a redbed spoil pile in a strip mine. The man's companion, surveying the stuck victim, was holding an impotent-looking spade and appeared ready to start rescue operations. The victim, to repeat a worn cliché, "was not amused" with the epithet "old stick-in-the-mud." An offer for assistance was dismissed as unnecessary, and apparently so, for an hour later when I passed the site again both were gone. I might add that this is the only instance I have witnessed where a "beast" has become entrapped in a redbed quagmire.

But landsliding, not entrapment, has been the bane of those building roads or structures resting on redbeds. Even in undisturbed areas, these beds readily slip, slide, and flow downhill. In fact, the translation for the Native American name Monongahela means "river of the caving bank." However, any cut exposing redbeds enhances conditions favorable to landsliding, as many builders have learned. Regionally, the Appalachian Plateau is second only to California in losses from landslides. So, as long as we inhabit the Appalachian Plateau, we will continue to hear the re-echoing of the statement, "it's those d----d redbeds."

--Richard M. DeLong

Editor's note: Richard M. DeLong retired from the Survey in 1988 after 34 years of trudging across the redbeds of eastern Ohio.