Hemmed-In-Hollow Falls is a 209-foot single-drop waterfall in the Ponca Wilderness of the Buffalo National River in northern Arkansas, regarded by the National Park Service as the tallest waterfall between the Rockies and the Appalachians. It drops into Hemmed-In Hollow, a small valley ringed on three sides by high bluffs that give the place a canyon-like enclosure. The flow is often light and can nearly disappear in dry weather, but after heavy rain, especially in late winter or early spring, the falls become much more powerful. Reached only by trail or from the Buffalo River, the site is known for both its dramatic setting and strenuous climb.