It took but a few minutes on June 23, 1925, for part of the side of the mountain to come sliding down. The location was just south of the Gros Ventre River in Teton County. The rockslide happened after a prolonged period of exceptionally heavy precipitation.
An estimated 50 million cubic yards of sandstone from the Tensleep formation roared down, blocking the Gros Ventre River, and forming a dam and what was to become Lower Slide Lake.
Less than two years later, again after heavy rains, a second disaster struck. The top sixty feet of the earthen dam created by the Gros Ventre rockslide gave way, and flood waters poured into the small town of Kelly. The torrent killed six people and flood waters reached nearby Wilson. A 50-ton steel bridge was sent downstream, twisted like spaghetti. Some people caught up in the floods were swept up into trees. Kelly was decimated. Only a few buildings survived.
Learn more about the 1925 Gros Ventre Slide and the 1927 Kelly Flood in the Orrin and Lorraine Bonney papers at UW’s American Heritage Center.