Inbounds within the ski area boundary. Groomed trails are generally safe from this. But watch for these small trees on the sides of the groomers; several fatal accidents have occurred within a few yards of groomed trails. I had an encounter with a snow bridge at Timberline one night early in the season. To the right of Vicky's Run is a small bluff that makes for a great natural kicker. I hit it hard and launched myself out into what looked like soft deep pow. What it turned out be was a giant snow bridge supported by thick, tangled 3 to 4 foot high pine saplings. I was tangled up in them that it took me forever to get out. I was in sight of the main trail and not more than 20 feet from it. Had I landed on my back, I could have gone in upside down easily.
On mount washing
I've once fallen into a 15 foot hole on the side of a groomer, but still within the runs boundries. It didn't make any sense how or why it was there, it was just a big open hole about 12 foot across 15 feet deep that went down to rock. There was i think 620cm base at that time. I fell into it because i was turning to head into the glades and i followed some ski tracks that went over a tiny roller, i got to the top and it was just like a small cliff.
another time I was going down a different run with some buddies and suddenly my friend did what looked like someone jumping for their life, and we stop and there's this black hole that went straight down about 4 foot across that my friend jumped over, no marking or anything, so we start riding a little more cautious and we come across 4 more of these holes that go down however many feet, like i said the snow base at that time was between 600-700cm. These where in the middle of a double black groomed run.