Great idea Charlie. For that trailhead, it is worth mentioning that you can simply continue on the Pratt Lake trail, rather than going up Granite Mountain. Pratt Lake wasn't safe yesterday, but it was a lot safer.
Fred Beckey's book specifically mentions the dangerous nature of Granite in the winter. He also mentions that if you decide to go, you should stick to the ridge. I'm afraid these folks were ignorant of this advice. My guess is that they just looked at a map and decided to go.
The Commonwealth Basin accident is, in many ways, more alarming. Commonwealth Basin would probably be one of those places on that sign that would be recommended. Of course, just about any snowshoe or ski book will tell you not to go too far towards Red Mountain if the snow is unstable. It is like Gold Creek Basin -- a great place for kids and novices to play in the snow but you need to know when to turn around.
My advice to people when they ask about getting out in the snow is to buy a guide book and stick to those spots. It isn't like the summer when you can just grab a Green Trails map and go. The books do a good job of explaining where the likely avalanche spots are. If a route (like Granite) is not mentioned in a snowshoe book, chances are it is dangerous. Of course you don't want to rely too much on the books (and assume a spot is safe because the route says so) but the books also mention that as well.
