In 1959, a 7.3 quake hurled a landslide across Montana’s Madison River: 67 years later Earthquake Lake still floods the valley west of Yellowstone

An earthquake struck southwestern Montana late on August 17, 1959, with a force that would permanently alter part of the landscape west of Yellowstone National Park. The Hebgen Lake earthquake, now officially described by the U.S. Geological Survey as magnitude 7.3, occurred at 11:37 p.m. local time near the western boundary of Yellowstone. A huge section of the canyon's south wall broke loose and crashed into the valley below. The debris crossed the Madison River, surged partway up the opposite canyon wall and formed a natural dam, and water soon began collecting behind it. That newly blocked stretch of river became Earthquake Lake, which remains in the valley today. The USGS says the earthquake caused 28 deaths, most associated with the massive landslide in Madison Canyon.

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