Just out of the gate from 9990, ~200 yards North of the gate along to top of the ridge. Appeared natural, no tracks leading into it and we saw no skiers near it as we watched each other ski down on opposite sides of the slide some distance away. It seemed to have occurred while we were doing our runs nearby on opposite sides. I may have triggered it remotely skiing along the top of the ridge. Called it in to Alta Central and asked them to tell Canyons Ski Patrol.