I just did the CB-Aspen race, called the Elk Mountain Grand Traverse. 40 miles, 7000+ feet of vertical, starts midnight. The winners do it in 8 hours, others take up to 16 hours.
It was a great event. Neat course. Well organized. For people who are into back-country skiing, I recommend this. But, make sure you are ready.
It's at the end of March every year. More info here: Grand Traverse