Boulder Rez Marathon

On a spring morning in Boulder, roughly 300 runners gather at the Boulder Reservoir for a half marathon that showcases the best of Colorado's Front Range. The course, mostly on packed dirt trails, hugs the shoreline and offers constant views of the Flatirons and the Continental Divide. At just 200 feet of total elevation gain, it's a flat, fast loop—runners complete two circuits for the half, while a 10K does one loop and a 5K takes a separate route. Temperatures average a crisp 33°F start rising to 61°F, with low humidity and scant rain, ideal conditions for a PR attempt.

The race has grown steadily since its 2015 debut, drawing athletes from four states and earning a loyal following—about 6 percent of runners return each year. The atmosphere is low-key but spectator-friendly, with clear views of the course from the shore. The finish line treats runners to a glamorous medal and the chance to explore Boulder's famous restaurants and trails. USATF certified and perfectly paced, it's a hidden gem that delivers big scenery without the big crowds.