Past and current hydrothermal activity at Yellowstone National Park altered and weakened the rhyolite, making the rocks softer. The Yellowstone River eroded these weakened rocks to deepen and widen the canyon, a process that continues today. The current canyon begins at Lower Falls and ends downstream from Tower Fall. Here is a view of the Lower Falls.
A stone engraving at the New Castle Historic Society building, New Castle, Delaware, depicting a hawk and a canyon, possibly signifying strength during war