Trail running enthusiasts will find the Colossal Vail 50/50 an exceptional desert ultrarunning experience in southern Arizona’s high desert. Organized by Fleet Feet Tucson and the Arizona Trail Association, this December event takes place in Colossal Cave Mountain Park, 24 miles southeast of Tucson, and forms part of the prestigious Arizona Triple 50 series.

The event offers three distances: 50-mile, 55K (34 miles), and half marathon options including a unique nighttime version. All courses follow out-and-back routes along the Arizona Trail, starting and finishing at La Posta Quemada Ranch. The terrain showcases the Southwest’s varied desert landscapes, from saguaro-studded flats to limestone canyons and riparian zones along Cienega Creek.

The 50-mile course features 4,000 feet of elevation gain, reaching a high point of 4,200 feet with expansive Santa Rita Mountain views. Runners pass through dramatic limestone formations and navigate tunnels beneath I-10 and Highway 83. The 55K shares much of this route with 3,000 feet of climbing, while both half marathon distances offer faster, more accessible terrain.

What distinguishes this event is its runnable desert trails and strategic aid station placement every 4-6 miles, stocked with Tailwind Nutrition, real food, and hydration. The course design emphasizes speed over technical difficulty, making it ideal for personal records or first-time ultra attempts.

The intimate 300-runner field limit creates a community atmosphere enhanced by the post-race celebration at the ranch. Cutoff times are generous: 14 hours for the 50-mile, 11 hours for the 55K. The December timing provides ideal desert running conditions with cool temperatures and clear skies.