Snowmobilers rode up Ephraim Canyon mid day and the avalanche had not occurred yet. They did some riding and were working their way back down in adjacent terrain to the avalanche path. They were a few hundred yards away. They worked their way down through the trees and when they came to the run-out zone of the path, it was filled with fresh debris. There was no wind loading or heavy snowfall so the most likely trigger was the snowmobilers when they were in the adjacent terrain to the path.