If it was a 70 degree slope they needed rock climbing gear for winter
My guess is they were somewhere by mistake or should have turned back
I knew someone who died in an ice chute fall in the same area. He took a pack of young Scouts up to the mountains over a winter break. One of the kids stepped off of a trail and began to slide, the Scoutmaster went to rescue him and stepped on an ice chute and fell to his death
Wrightwood is a town up in the mountains that I know a bit. My guess is that these people were hiking rather doing anything like mountain climbing. The 70% slope would likely have been next to their trail rather than something they were climbing. The ice chute is what made it deadly, especially in the weird weather that we have had here lately. Maybe atc23 has an idea of what their trail was like.