June 7, 2025
June 23, 1925, the north slope of Sheep Mountain, aka Sleeping Indian, collapsed and sent 50,000,000 cubic yards of debris hurtling down its flanks. Today, the scar is still fresh enough to be seen from miles away. The Gros Ventre Slide, which is in the Jackson Ranger District of the BTNF, was one of the largest, fastest-moving landslides in the world. In just three minutes, 50 million cubic yards—enough to cover the entirety of Washington D.C. six inches deep—of rock, soil, and other debris slid down from an altitude of 9,000 feet. State Surveyor W.O. Owen estimated that the builders of the Panama Canal could have gotten their jobs done in 54 minutes had they been able to move earth at the speed of the Gros Ventre slide. The Gros Ventre debris made it to the bottom of the mountain, dammed the Gros Ventre River, and continued 400 feet up the opposite slope. This new dam—2,000 feet wide, a mile long, and 225 to 250 feet high—on the Gros Ventre created a five-mile long lake, Lower Slide Lake.
Although engineers, geologists and various scientists pronounced this natural dam safe, it was breached in May, 1927 and flooded the community downstream, Kelly, with 15 feet of water. Six people died and most buildings were washed away. The floodwaters were massive enough to even wet Jackson’s streets, 12 miles distant.
Today the foot of the slide is the Gros Ventre Slide Geological Area. To celebrate National Trails Day and mark the 100th anniversary of the slide, the BTNF is looking for volunteers from 9 a.m.–12 p.m. at this site to help rehab trails and signs and, working with Teton County Weed + Pest, pull invasive species.
Lunch and speakers start at the site at noon.
If you’re able to help out, please RSVP to Hannah Jacobson by May 26: hannah.jacobson@usda.gov or 307/739-5587
