If you stood at the Cleland Rock Vista 200,000 years ago, you would be standing on a ridge at a drainage divide. Water to the north flowed north and water to the south flowed south.
If you stood at the same location about 140,000 years ago, you would be standing at the edge of a small lake dammed by several hundred feet of ice. The ice was the edge of a continental glacier that covered most of North America north of Cleland Rock. The glacier dam created small Lake Prouty by Cleland Rock. To the north was larger Lake Watts (modern Lake Arthur is a small re-creation of Lake Watts) and further north was giant Lake Edmund.
Eventually Lake Prouty spilled over the ridge near Cleland Rock and began carving Slippery Rock Creek Gorge. As the glacier retreated, Lake Watts drained into the channel, enlarging and deepening the gorge.
Lake Edmund swiftly poured into the channel, scouring the gorge to over 400 feet deep. When the glacier finally retreated back to the north, Slippery Rock Creek Gorge was so deep that streams that normally flowed north, now flowed south, as the streams do today.
The rapid erosion of the gorge created its swift water and exposed the many boulders that offer great challenges to modern whitewater boaters.
Detailed information about the glacial geology of the area is available from:
Trail of Geology - Moraine and McConnells Mill State Parks Guide (PDF)
This driving tour brochure corresponds to numbered posts throughout the park and surrounding area.
Which Rock is Slippery Rock?
Slippery Rock Creek is 49 miles long and full of slippery rocks, yet is named for one exceptionally slick rock below the Armstrong Bridge. It is believed that an Indian trail forded the creek at a shelf of sandstone near a natural oil seep, which made the rock exceptionally slippery, and gave its name to the creek, a town, a university, a rock formation and many local businesses.
During the late 1800s, oil wells briefly flourished in the valley, but the oil was swiftly invaded by groundwater and the wells were abandoned. The oil wells drained the oil seep and the Slippery Rock is no longer covered in oil.
Slippery Rock Gorge Natural Area
The 930-acre Slippery Rock Gorge was designated a National Natural Landmark by the U.S. Department of the Interior in 1974 and became a State Park Natural Area in 1998. The steep-sided gorge contains numerous rocky outcrops, boulders, old growth forest, waterfalls, and rare plants.
Cleland Rock Vista is a great place to view the gorge.
Also part of the natural area, Hells Hollow has a wide array of wildflowers, waterfalls, and habitats in addition to what can be found in the Slippery Rock Creek Gorge. A one-half-mile hiking trail leads to a cascading waterfall and an old limekiln.