The sedimentary rocks of the canyon walls are believed to be the remains of the ancestral Appalachian Mountains. These mountains were eroded into inland seas during the Devonian Period 350 million years ago. Along the course of the Genesee River, on its three-day journey from Pennsylvania to Lake Ontario, over 100 million years of deposition are revealed in the rock layers, like pages of geologic time.
Alternating strata of sandstones and shales offer a variety of soft-colored hues in the vertical cliff in front of you. Some shales are dark from highly organic clays, which have a fuel-oil odor caused from decayed plants and animals. Other rusty-brown bands contain oxidized minerals, such as iron.
Midway down this 350-foot cliff, a year-round spring is creating a huge stalagmite weighing several tons. This centuries-old rock, "growing" from precipitated lime mixed with algae and moss, is called tufa.