Trail Running calendar near Boulder 2025-2026

The Greenland Trail Races, held annually in May at Greenland Open Space in Larkspur, Colorado, offer four trail running distances: 4 miles, 8 miles, 25K, and the 50K ultramarathon, known as Colorado's fastest 50K. The course features wide, smooth dirt trails through native grasslands, ponds, oak hil..

Endure Trail Runs, the 6th annual Mueller State Park event in Divide, Colorado, centers at the Pisgah Point Group Campground. It features a unique 12-Hour Endure timed challenge, where runners draw colored balls to decide the next loop and accumulate miles within the allotted time. In addition, 10k,..

The Weld Your Mettle Running Festival, held in Eaton, Colorado, is a multi-day event featuring a variety of running challenges for all levels. Participants can choose from solo or relay races lasting 3, 6, 9, 12, 24, or 36 hours, including a 100-mile ultra with a 36-hour limit. Unique formats like t..

North Fork 50 Mile/50K is an ultramarathon set in the Colorado mountains just southwest of Denver, near Buffalo Creek. The event offers two distances: 50 miles and 50K. The course is 100% soft-surface, comprised mostly of singletrack trails with a few short sections of double-track road.Runners clim..

Crazy Legs 10k+ Trail Run takes place at Devils Backbone Open Space in Loveland, Colorado. The six-mile loop uses mostly single-track and includes a few doubled sections to limit backtracking. Runners traverse Hidden Valley, Hunter Loop, Laughing Horse Loop, and Wild Loop before finishing in the Dev..

The Summits Trail Runs, held at Granby Ranch Resort in Colorado's Rocky Mountains, offer a challenging and scenic trail running experience with distances from 6 miles to ultra distances including a 50k and a 12-hour Elevation Challenge. The courses feature rugged alpine terrain, single-track trails,..

The Timberview Trail Run is an annual trail running event held at Lory State Park in Bellvue, Colorado. Celebrating its 7th year in 2026, the race offers three distances: 5K, 5 mile, and 10 mile, catering to all levels from beginners to experienced trail runners. The scenic course features trails th..

Silverheels Trail Runs, the 12th annual event from the Human Potential Running Series, unfolds in Colorado, with races including 100k, 100-Mile, 50-Mile, 60k, 19-Mile, and 10-Mile. The revamped format places the main event at the Como Roundhouse in Como, CO, while the 100-Mile and 100k start at Burn..

The Summit 200 is a single, non-repetitive 200‑mile loop around Summit County, Colorado, centered near Frisco. The mostly non-urban route uses single-track trails, forest roads, and some rec paths and pavement, with the lowest altitude above 9,000 ft and sections climbing toward 12,800 ft, plus 12 f..

Sheep Mountain Trail Runs, part of the Human Potential Running Series, takes place near Fairplay, Colorado on the western slope of the South Park Valley. The 12th annual event offers 50-mile, 50k, and Half Marathon distances, with a 16-hour time limit and a 300-runner cap. The start/finish is at the..