Explorers Club

On Saturday, May 23, 2009, the Explorers met for a sunny morning hike through scenic Clifton Gorge near Yellow Springs, Ohio.

Clifton Gorge is a state nature preserve that encloses one of the most impressive geological sites in western Ohio. The gorge is the result of water flowing from melting glaciers to the north of the site at the end of the last Ice Age. This water began cutting a channel through the top layers of rock, and it is the nature of this type of rock that gave Clifton Gorge its current appearance.

The bedrock underlying this entire region is composed of various types of sedimentary rock, all laid down in layers during long-ago cycles when the area was covered in shallow seas. Different types of rock have different hardnesses, and flowing water finds it much easier and quicker to weather away and carve a channel through a softer type of rock than through a harder rock. In a softer rock, the water is able to not only carve its way downward, but it also wears away rock horizontally (to the sides), resulting in a broad valley through which a stream flows.

The stream flowing over the future Clifton Gorge, however, encountered a much harder type of sedimentary rock known as dolomite. A harder rock such as this means that once the flowing water has started a channel, it mostly can only carve down, with very limited horizontal cutting action. Rather than a broad valley, what results is a much narrower and deeper cut in the land--which is exactly what the Explorers discovered at Clifton Gorge.

The club members first hiked along the top of the gorge's rim. Stopping at several overlooks, they could easily see the layers of the dark dolomite rock on the opposite wall of the narrow gorge, with the Little Miami River flowing an impressive distance below. They next descended a steep staircase and trail in order to walk along the river at the bottom of the gorge.

As they walked downstream, Mr. Ramsey told the Explorers to watch for the changing character of the gorge. It shortly became apparent, as the walls grew increasingly further apart and the gorge became wider and wider. The rocks at ground level also began changing character, becoming lighter in color and much more broken and gravelly underfoot.

This is because below the layers of hard dolomite rock are layers of much softer sedimentary rocks. Once the stream managed to cut its way through the dolomite it encountered these softer layers and was once again able to begin cutting more aggressively in a horizontal manner. Once that happened, the dolomite began to be undercut. Mr. Ramsey had the club members imagine digging sideways into a wall of dirt to understand what this means--sooner or later you would dig far enough back that the dirt hanging above would collapse on top of you.

This is what has happened in the lower reaches of Clifton Gorge. As the stream cuts sideways into the softer rocks below, the hard layers above eventually collapse under the strain of their own weight. Several types of evidence for this can be found at Clifton Gorge, the most obvious of which are huge blocks of rocks, many far larger than a house, which have tumbled down from the walls above into the stream.

The Explorers soon encountered the second type of evidence of undercutting. In numerous spots, chunks of rock that have broken and slipped down the wall have formed what are known as slump-block caves. These are recesses along the wall where big pieces of rock are lying against and in front of the wall, with narrow passageways and spaces in between. The Explorers investigated a set of these caves, which was one of the highlights of the day's outing.

Leaving the slump-block caves behind, the Explorers soon reached a foot bridge spanning the Little Miami River. At this spot the state nature preserve ends, but the trails continue into the adjoining John Bryan State Park. This spot, though, marked the turn-around point for this particular hike. The Explorers spent some time searching for interesting rocks and shells along the stream's edge, and then it was time for the walk back upstream to the trailhead.

For photos of the hike through Clifton Gorge, click on the gallery link below.

Gallery

For information on visiting Clifton Gorge and the adjacent John Bryan State Park, click on the links below.

Clifton Gorge State Nature Preserve

John Bryan State Park