Vanport Limestone Ledge
By the time Hell Run flows over Hells Hollow Falls, it has eroded through the Vanport Limestone into the underlying Clarion Formation. The Vanport Limestone can be seen as picturesque ledges in the walls of the gorge above the falls. Groundwater flowing through fractures and small caves discharges from these ledges. In the winter, the groundwater discharge forms large icicles and ice columns below the ledge.