Gravel Mountain, north of Granby, is a popular area for snowmobiling. Numerous riders from multiple groups had been riding in the area. There were many snowmobile tracks on the slope that later avalanched. There were three different groups of riders in the immediate area at the time of the avalanche. Group 1, a group of four snowmobilers, were climbing one at a time from the bottom up onto the cornice, turning around, and then riding off the cornice. Group 2 was riding on the slope to the north. Group 3 was watching from the bottom of the slope.

Three riders from Group 1 were sitting on their snowmobiles about 10 to 15 feet back from the edge of the cornice, waiting for the fourth rider to join them on the top. The fourth rider had just crested the top of the cornice when they felt a collapse. The snow under their machines fell away, and three of the riders fell over the edge as the cornice broke and the slope below avalanched. One of the riders in Group 1 was caught in the flowing avalanche debris and pulled his avalanche airbag. When the debris came to a stop, he was partially buried with his head above the snow. The other two riders from Group 1 managed to self-arrest on the bed surface below the cornice, but their snowmobiles were pulled downhill by the debris.

A rider in Group 2 jumped off the cornice, likely not seeing the avalanche on the slope below. He inadvertently rode into the flowing debris. When the avalanche came to a stop, he was partially buried with his head above the snow. Riders from Group 3 at the bottom of the slope scattered and rode away as the avalanche ran toward them. No one in Group 3 was caught. Four riders from two different groups were caught. Two were partially buried, but luckily, nobody was injured.

Grand County Sheriff's Office received a call about a "massive avalanche.” They initiated a search and rescue response. Grand County Search and Rescue team rode to the site and interviewed bystanders.