09/06/2026
Did you know that some canyon walls hold the secrets to ancient, vanished rivers?
Take a close look at the cliff line in this photo from Washington’s Grand Coulee. See that distinct dip along the top rim that just stops in mid-air? That is a geological feature known as a hanging valley.
During the last Ice Age, catastrophic megafloods from Glacial Lake Missoula tore through this region. The immense hydraulic force rapidly plucked away massive layers of dark columnar basalt, dropping the main canyon floor by hundreds of feet in a matter of days. This left smaller, pre-existing side valleys stranded high up on the new cliff walls.
When geologist J Harlen Bretz used these perched channels to argue for a massive ancient flood in the 1920s, his peers were highly skeptical. Decades later, modern science proved him right, turning these volcanic cliffs into a masterclass in Earth history.
Have you ever spotted one of these unique formations while exploring the Ice Age Floods National Geologic Trail? Let us know in the comments!
NPS Image
