The event starts at 10 PM on a bridge over the Arkansas River at 7,000 feet elevation. Participants ride through the night, and most of them through the entire next day never dropping back below 9,000 feet until the last 8 miles. The course draws a large circle through some of the highest mountains in North America. There are multiple high points near or above 12,000 feet. There are six long sustained climbs that each can take 2 hours or more to complete.