The party was in Bells Canyon, they determined a safe spot, which 3 members of the party had stopped by, as the 4th member came into the chute, the entire thing slid. Two of the members got off the slab and ended up right at the crown, one of the other members grabbed hold of a tree, the other slid quite a ways down, grabbing onto a tree, until a rather large block came down and smashed him off the tree. After sliding down a little bit further, he was able to dig into the bed surface. This was reported to me by the member of the party who had to grab onto a tree and was hit off by a large block. He reported the crown being 2 feet deep and approximately 50 feet wide.