A short hike along the Hells Hollow Trail toward Hells Hollow Falls passes a number of features related to the Vanport Limestone and the old iron industry that flourished in the valley of Slippery Rock Creek during the mid-1800s.
In the streambed adjacent to the parking lot, sharp distinct fractures cut the Vanport Limestone. During dry periods, no water flows in the stream here, but flows in a small cave, formed by dissolution of the limestone.
The Lawrence Iron Furnace was a few hundred feet upstream from the third bridge of the Hells Hollow Trail. All that is visible today are some of the slag piles from the furnace.
After you cross the third bridge, a small coal mine entrance, abandoned for over 100 years, may be visible high on the hill across Hell Run.
Farther along the trail toward the falls, you pass a spot where Hell Run flows in a narrow flume in the limestone that was originally a cave. With time, the roof collapsed and exposed the hidden channel.
Small depressions near the trail along this section are sinkholes, also formed by limestone dissolution.
Just upstream from the falls, you encounter a small quarry where iron ore and limestone for flux were probably mined for the Lawrence Furnace.
Shortly beyond this, the trail ends at Hells Hollow Falls, a picturesque cascade over resistant sandstone in the Clarion Formation.
The Vanport Limestone is now visible as ledges along the gorge walls.
To the right of the falls is a brick-lined vertical shaft cut into the rock. This is a lime kiln that burned limestone, probably from the quarry, to produce lime.
Another longer and more rugged trail, the Slippery Rock Gorge Trail, follows the north side of Hells Hollow. It also has geologic features, including old coal mine entrances, Vanport Limestone outcrops, natural limestone bridges, small caves, and emerging underground streams (see map above).