The Audi Power of Four Race Series, which takes place tomorrow, March 2, is not for the faint of heart. It is a punishing endurance race series utilizing the unique terrain of each of the four Aspen Snowmass mountains. The race is designed to test the limits of both elite and recreational athletes, with two races geared for each level of participation. This year for the first time, the race is the United States Ski Mountaineering Associations's national championship. That's a real feather in everyone's cap. With the heavy snow expected to continue through Sunday, conditions should be especially challenging for participants.