Boulder Rez Marathon 2026

The Boulder Rez Marathon takes place in August at Boulder Reservoir in Boulder, Colorado. The race starts and finishes at the reservoir park area on 51st Street. This event is a trail-and-dirt-road race series, offering marathon, marathon relay, three-quarter marathon, half marathon, and 10K distances. The full marathon begins first in the early morning, with shorter races starting shortly after. The course remains open until early afternoon. Most of the route follows dirt roads, packed-dirt trails, some singletrack, and paved park roads near the start and finish, running beside or around Boulder Reservoir. The course is notably flat for Boulder, featuring approximately 200 feet of elevation gain. The primary challenge lies in maintaining a steady pace over mixed surfaces, rather than significant climbing. The race is USATF sanctioned, with measured and marked courses. Participants receive finisher medals and shirts, along with overall and age-group awards. Post-race activities include music, awards, beer, and food. Volunteers can be of any age, though those under 13 require adult supervision.