The 390-million-year-old fossil beds are among the largest, naturally exposed, Devonian fossil beds in the world.The "Falls" was originally a series of rapids allowing the Ohio River to drop 26 feet over a distance of two and a half miles. This was the only navigational hazard over the 981 mile-length river formed by rock outcrops. Today much of the original falls have been flooded behind the McAlpine dam.