Monument Valley, the Grand Canyon, Niagara Falls: these ancient wonders show how nature’s forces have shaped the face of our planet on a vast timescale, how great landmarks are the work of millions of years of slow, imperceptible erosion by wind and water.

But here, across 16,000 square miles of Washington State, abrupt rips and scars in the landscape defy this explanation. What could have formed these tall canyons and immense dry waterfalls? What could have gouged out these gigantic potholes? Whatever happened, the forces unleashed here created one of the Earth’s most enigmatic landscapes.

For more than a century, scientists have been grappling with this geological mystery, descending through thousands of years of Earth’s history in a struggle to uncover, layer by layer, how this landscape was formed. Now the clues point to a sequence of events culminating in a massive natural catastrophe.

Explore the features and reasoning that lead to the recognition of the “Missoula (Outburst) Floods” and helped to solve “The Mystery of the Megaflood (Spokane Floods or the Bretz Floods)”