The Gorge
As you look down into the gorge you can see two distinct types of rock, even if you can't tell them apart from here. The bottom layer is known as Blackhand Sandstone, a sulfur and quartz-rich rock found almost exclusively in the Hocking Hills region. Blackhand Sandstone was first identified in Blackhand Gorge in Licking County, named after a “hand”- shaped petroglyph believed to have been carved by Native Americans to guide travelers. The top layer of rock is Logan Shale, a geologic formation composed mainly of sandstone, siltstone, and other types of shale. It's noticeably softer and lighter in color than the sandstone and was allegedly named in honor of Chief Logan, a Native American leader. But why is this dramatic gorge here? In the middle of gentle rolling hills?
Power From the Past
Ohio’s last ice age occurred during the Pleistocene Epoch, which spanned from about 2.5 million to 11,000 years ago. During this time, the Wisconsinan Glacier advanced into Fairfield County, carving out much of the landscape. The gorge, however, was not created by the glacier's advance, but by its retreat. As the glacier slowly melted, the hills just to the notrth and south funneled the melt water here between them. The rushing current of frigid water from ice a mile thick is what carved the gorge and pit at its bottom on its way south to the Ohio. The glacier also caused the giant crack you can see running from one side of the gorge to the other as the immense weight of ice broke apart the rock beneath. This crack may also be why there are many natural springs in the gorge, as it provides a path for ground water through the rocks above it. When the mill is open, visitors can take a path down into the gorge where you may be able to see water coming from the rocks yourself.
The Gorge Today
As you can see though, the power of water didn't stop 10,000 years ago. Rock Mill still harnesses the great power of the Hocking River to turn stones and grind corn. The mill's original constructors of the mill also carved the straight channel in the rock above the falls to the left. A reminder that humans too make their mark in Earth's geologic record.
Now the gorge is reletively quiet. Free from the industrial work of the 1800s and the rushing torrent of melting glaciers. Now the next chapter of the gorge will be written by the plant and animal life that lives here. Northern Rough Winged Swallows nest within the crevices in the sandstone next to the plethera of ferns. Aquatic turtles and a variety of fish inhabit the pools below the falls. Logs rolled into the gorge by storms create new pools and rapids depending on where they land. Even in the fastes riffles aquatic insects, salamanders, and crayfish can be found.
Logging Tasks
Now that you have learned more about the area, answer the following questions to log this EarthCache:
- Based off your observations does the Blackhand Sandstone or the Logan Shale seem more easily erroded?
- Describe the color of the Hocking River. Do you think it looks different than it did when its source was glacial meltwater?