From the event website:
This unique mountain bike race combines the four ski areas of Aspen/Snowmass (Snowmass, Buttermilk, Aspen Highlands and Aspen Mountain) into one amazing mountain bike race. The diversity of the terrain and tackling our four distinct mountains has placed this race in a category all its own.
The field consists of solo racers and relay teams (of two or four) from the avid bike community that exists in Aspen/Snowmass, Colorado and beyond. Racers will start at the base of Snowmass and finish at the base of Aspen Mountain in Gondola Plaza. With 9,000′ vertical gain and drop over 36 miles on top-rated single track, demanding double track ascents and coverage on each of our four mountains this race will challenge even the fittest riders. Experience the Power of Four!