Eight snowmobilers were riding on Forest Service road 311, north of Dumont Lake, near Rabbit Ears Pass. All the riders were carrying avalanche rescue gear as well as BC-Link two-way radios. Almost all wore avalanche airbag backpacks.
As they approached a steep south-facing slope, the last two riders stopped and waited to hear confirmation that the first six had crossed safely. Riders 7 and 8 saw the avalanche occur. They were unable to assist the rest of the party immediately, as they both got their snowmobiles stuck attempting to cross through the avalanche debris.
The Riders 1 and 2 crossed the slope first. The avalanche did not hit them. The avalanche hit Rider 3, who was partially buried and able to self-rescue. Riders 3 communicated with the rest of the party and determined that Riders 4 and 5 were missing. Rider 3 organized the rescue with Riders 1, 2, and 6.
The group performed an effective beacon search. They located, probed, and dug out Riders 4 and 5 in 10 to 15 minutes. Rider 4 had been pinned under their sled. Rider 4 was able to move enough under the snow to maintain radio contact, letting the group know they was able to breathe. Rider 4 had been unable to deploy their avalanche airbag. Rider 5 was buried face down in a tree well, with their airbag deployed.
The avalanche was a soft slab, unintentionally triggered by a snowmobile. It was medium relative to the path, capable of burying a person, and broke at the ground (SS-AMu-R3D2-G). The avalanche was between 600 to 800 feet wide, averaged 3 feet deep, and ran 200 vertical feet. It started at an elevation of 10400 feet, below treeline, on a south aspect.
The reporting party's original observation.