Blue Sky Trail Marathon & Half Marathon 2026

The Blue Sky Trail Marathon & Half Marathon is a September trail-running series held near Fort Collins, Colorado. It offers half marathon, marathon, and 50K distances. All races begin in Horsetooth Mountain Open Space in Larimer County. The marathon starts and finishes at the Blue Sky Trail trailhead. The majority of the course is on singletrack, with sections of gravel paths and rough, rocky terrain. The route crosses Horsetooth Mountain Park and Devil's Backbone Open Space, providing a foothills environment instead of a road-race atmosphere. The marathon has a 9-hour time limit, and this series has been held annually since 2008.