Denver’s running scene is defined by altitude, mountain backdrops, and a fiercely passionate community of runners who embrace the challenge of racing at 5,280 feet above sea level. From the iconic Colfax Marathon — the only race that sends runners through Denver Zoo with elephants and giraffes watching — to the 50,000-person BolderBOULDER 10K in Boulder and legendary trail ultras in the Rocky Mountains, Colorado delivers some of the most spectacular racing in the country. The mild, sunny winters also make Denver a year-round running destination, with strong club culture and a race nearly every weekend.
Road Races in Denver
Horsetooth Half Marathon
The 53rd Annual Horsetooth Half Marathon is Fort Collins’ premier spring race — a point-to-point course dropping 1,154 feet from the canyons above Horsetooth Reservoir to the finish at New Belgium Brewing, with $12,000 in prize money and one of Colorado’s most competitive half marathon fields.
Date: Apr 19, 2026 | Distances: Half Marathon (13.1 mi) | Location: Fort Collins, CO | Official Site
Slacker Half Marathon
Colorado’s legendary all-downhill half marathon starts at 10,630 feet at the base of Loveland Ski Area and drops nearly 2,200 feet through enchanting wetlands, historic mining ruins, natural waterfalls, and Continental Divide views before finishing in charming Georgetown.
Date: Jun 27, 2026 | Distances: Half Marathon (13.1 mi), 4 Mile, Relay | Location: Georgetown, CO | Official Site
Georgetown to Idaho Springs Half Marathon
One of Colorado’s oldest half marathons, the 48th Annual Georgetown to Idaho Springs Half Marathon follows the historic Argentine Central Railroad corridor through Clear Creek Canyon, connecting two iconic Colorado mountain towns with 13.1 miles of scenic mountain valley running.
Date: Aug 08, 2026 | Distances: Half Marathon (13.1 mi) | Location: Georgetown, CO | Official Site
Colorado Marathon
Billed as Colorado’s fastest downhill marathon, the Colorado Marathon follows the stunning Poudre River Canyon from the Rocky Mountain foothills into downtown Fort Collins — a scenic point-to-point course beloved for its waterfalls, canyon walls, and strong finishing atmosphere at Washington Park.
Date: May 02, 2027 | Distances: Marathon (26.2 mi), Half Marathon (13.1 mi), 10K, 5K | Location: Fort Collins, CO | Official Site
Colfax Marathon
Denver’s only marathon and biggest race weekend takes runners along the legendary Colfax Avenue — America’s longest commercial street — through Empower Field at Mile High, a full mile inside Denver Zoo, and a spectacular City Park finish with 25,000 fellow runners.
Date: May 16, 2027 | Distances: Marathon (26.2 mi), Half Marathon (13.1 mi), Urban 10 Miler, Marathon Relay, 5K | Location: Denver, CO | Official Site
BolderBOULDER 10K
America’s most celebrated 10K and one of the largest Memorial Day running events in the world, the BolderBOULDER finishes inside CU’s Folsom Field stadium with a soaring military tribute and pro race finale beneath the Flatirons.
Date: May 31, 2027 | Distances: 10K | Location: Boulder, CO | Official Site
Cherry Creek Sneak
Denver’s beloved springtime tradition held the last Sunday of April in the upscale Cherry Creek North neighborhood, the Cherry Creek Sneak is a festive multi-distance event with costumes, live music, a craft beer garden, and courses winding through the boutique shopping district.
Date: Dec 31, 2027 | Distances: 10 Mile, 5 Mile, 5K, 1.5 Mile Sprint, Kids’ Fun Run | Location: Denver, CO | Official Site
Trail Races in Denver
Quad Rock 50 & 25 Mile
The Quad Rock 50 and 25 mile trail races in Lory State Park west of Fort Collins are a beloved Front Range test of mountain fitness — 85% technical singletrack through the northeastern Rockies with stunning views from the Great Plains to Longs Peak, put on by trail runners for trail runners.
Date: May 09, 2026 | Distances: 50 Miles (11,000 ft gain), 25 Miles (5,500 ft gain) | Location: Bellvue, CO | Official Site
Vail Hill Climb
The 50th Annual Vail HillClimb is a legendary alpine race that climbs 2,128 feet from Vail Village to the Mid-Vail gondola station at 10,254 feet on July 4th weekend, following the same historic gravel service road used since the event’s founding in 1976.
Date: Jul 05, 2026 | Distances: 12.2K (7.6 miles) | Location: Vail, CO | Official Site
Aspen Backcountry Marathon
Set amid the spectacular Elk Mountains above Aspen, this Aravaipa Running event offers three trail distances — 50K, marathon, and heavy half — almost exclusively on dirt trails with jaw-dropping views, challenging ascents and descents, and a festive post-race celebration in Rio Grande Park.
Date: Aug 01, 2026 | Distances: 50K, Marathon (26.2 mi), Heavy Half Marathon (~15 mi) | Location: Aspen, CO | Official Site
Leadville Trail 100 Run
The legendary ‘Race Across the Sky,’ the Leadville Trail 100 is one of the most iconic ultramarathons in the world — a brutal 100-mile out-and-back through the Colorado Rockies at an average elevation above 10,000 feet, with a 30-hour cutoff and iconic silver belt buckle finisher awards.
Date: Aug 22, 2026 | Distances: 100 Miles | Location: Leadville, CO | Official Site
Telluride Mountain Run
A challenging and technical mountain race in the awe-inspiring San Juan Mountains above the historic mining town of Telluride, the race sends runners over mountain passes, exposed ridgelines, and high summits on old mining roads and alpine singletrack above 13,000 feet.
Date: Aug 22, 2026 | Distances: 65 Mile, Plus additional shorter mountain routes | Location: Telluride, CO | Official Site
Imogene Pass Run
The 53rd Annual Imogene Pass Run is one of Colorado’s most iconic mountain running events — a 17.1-mile point-to-point sufferfest crossing the 13,114-foot Imogene Pass through the heart of the San Juan Mountains from Ouray to Telluride.
Date: Sep 12, 2026 | Distances: 17.1 Miles (point-to-point, Ouray to Telluride over Imogene Pass) | Location: Ouray, CO | Official Site
Run Rabbit Run 50 & 100 Mile
The Run Rabbit Run 50 and 100 mile ultramarathons circumnavigate Steamboat Springs’ spectacular ski mountain and surrounding wilderness, crossing the Continental Divide to Rabbit Ears Pass, climbing Mount Werner, and traversing Emerald Mountain in one of Colorado’s most beloved fall ultra weekends.
Date: Sep 18, 2026 | Distances: 100 Miles, 50 Miles | Location: Steamboat Springs, CO | Official Site
Pikes Peak Marathon & Ascent
Billed as ‘America’s Ultimate Challenge,’ the Pikes Peak Marathon and Ascent are among the most demanding mountain races in the world, climbing 7,834 feet from Manitou Springs to the 14,115-foot summit of Pikes Peak and back on a relentless high-alpine route.
Date: Sep 20, 2026 | Distances: Marathon (26.2 mi, out-and-back to summit), Ascent (13.32 mi, to summit only) | Location: Manitou Springs, CO | Official Site
Crested Butte Ultra
The Crested Butte Ultra sends runners through the Gunnison National Forest on lollipop-loop courses with stunning wildflower meadows, mountain ridges, and epic fall foliage — one of Colorado’s premier mountain trail events set in one of the state’s most beautiful towns.
Date: Sep 26, 2026 | Distances: 50 Mile, 55K, 35K | Location: Crested Butte, CO | Official Site
Sage Burner Trail Race
The Sage Burner Trail Race in Gunnison’s stunning Hartman Rocks Recreation Area offers a unique high-desert trail running experience with technical slickrock, smooth singletrack, punchy climbs, and 360-degree views of the Maroon Bells, San Juan Mountains, and Gunnison Basin.
Date: Oct 03, 2026 | Distances: 50K, 15K | Location: Gunnison, CO | Official Site
HRCA Backcountry Wilderness Half Marathon
The 18th Annual HRCA Backcountry Wilderness Half Marathon winds 13.1 miles through the Highlands Ranch Backcountry Wilderness Area on singletrack trails and hills with breathtaking views of the Front Range, making it one of the Denver metro area’s premier fall trail races.
Date: Nov 07, 2026 | Distances: Half Marathon (13.1 mi) | Location: Lone Tree, CO | Official Site
Relay Races in Denver
Colorado Marathon Relay
The Colorado Marathon Relay runs teams through the spectacular Poudre Canyon — Colorado’s fastest downhill marathon course — from the Rocky Mountain foothills into Old Town Fort Collins, combining team camaraderie with one of the most scenic running corridors in the state.
Date: May 02, 2027 | Distances: Marathon Relay (26.2 mi, team format through Poudre Canyon) | Location: Fort Collins, CO | Official Site
Colfax Marathon Relay
The Colfax Marathon Relay is Denver’s premier team running event — five runners share 26.2 miles through the city’s most iconic landmarks including Empower Field at Mile High, Denver Zoo, and City Park in Corporate, Government, Public School, and Open relay divisions.
Date: May 16, 2027 | Distances: Marathon Relay (26.2 mi, 4 legs, teams of 5) | Location: Denver, CO | Official Site
From road races along Colfax Avenue to single-track mountain ultras, Denver and the Front Range offer one of the most exciting race calendars in the country. We keep this guide updated regularly at What Race To Run — click any event for full details, course maps, and registration links. Bookmark this page to track new additions and updated 2026-2027 dates.