Marathons in Colorado

In Colorado, altitude is the marathon — from Mile-High Denver's rolling Colfax to the brutal 14,115-foot Pikes Peak ascent, every start line sits in thinner air. The three races are listed below in date order, each with a live countdown.

Updated 2026-07-13 Sorted by race date. Field sizes and course data are checked against each race's official source.

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About marathons in Colorado

Air and gradient. Colorado's three marathons run one spectrum: thin air and climbing. Two spring road races sit at city elevation, where oxygen is the adjustment, not the hills — the canyon-fast Colorado Marathon in Fort Collins (early May) and Denver's flagship Colfax Marathon (mid-May), an out-and-back along East Colfax through City Park, past Empower Field at Mile High twice. September's Pikes Peak Marathon is another animal, climbing Barr Trail from Manitou Springs to the 14,115-foot summit and straight back down.

Altitude first, calendar second. Build any plan around elevation. Chasing a Boston qualifier or a PR? Fort Collins is the surprise — a net-downhill point-to-point through Poudre Canyon that the organizers bill as the state's fastest, dropping out of the high country before it flattens into town. It's the BQ-eligible pick here, so check your target with the Boston Qualifying calculator. But thin air still taxes the engine: sea-level runners should arrive several days early to acclimate, or race on arrival day before altitude fatigue sets in.

Treat the mountain as its own objective. Pikes Peak is a summit, not a time trial — train your downhill quads hard and respect the high-alpine weather. Each race uses its own official registration, and the bigger road events fill, so plan ahead. Denver and Fort Collins are an hour apart on I-25, so a single trip can stack both spring races; the page's live countdown cards and 'Updated' line keep dates checked against official sources.

Frequently Asked Questions

Which is the biggest marathon in Colorado?

The Colfax Marathon in Denver is the state's flagship event and its best-known city race, run each May along East Colfax Avenue through City Park and past Empower Field at Mile High. It draws the largest, most festival-like crowd of the Colorado races and serves as the natural starting point for most runners new to racing in the state.

Which Colorado marathon is fastest or best for a Boston qualifier?

The Colorado Marathon in Fort Collins is the standout. It's a net-downhill point-to-point that starts high in Poudre Canyon and descends roughly 1,200 feet before flattening into town — the organizers bill it as the fastest marathon in the state, and it's the BQ-eligible course on this page. The rolling Colfax Marathon is the next-best PR option, though Denver's roughly 5,280-foot start means the thinner air, not the terrain, is the real obstacle. Check your standard with the Boston Qualifying calculator. By contrast, the Pikes Peak Marathon is one of the hardest courses in the country and is never a place to chase a fast time.

When is the Colorado marathon season and how do I enter?

Colorado road marathons cluster in spring: Fort Collins in early May (around May 2) and the Colfax Marathon in mid-May (May 16). The mountain classic, the Pikes Peak Marathon, runs in September (around September 20), when high-alpine conditions are most manageable. Entry for each race is through its own official registration page; the larger events can sell out, so sign up well in advance rather than relying on race-week entry.

How does Colorado's altitude affect race day?

Every Colorado start line sits at elevation, so thin air is the defining factor. Denver and Fort Collins both start above a mile high, where there is meaningfully less oxygen than at sea level. The practical advice is to either arrive several days ahead to begin acclimating or, if you cannot, race on your arrival day before altitude fatigue and dehydration accumulate. Pace conservatively in the early miles, hydrate more than you would at home, and treat any predicted-finish target as optimistic until you have run at altitude before.

Which Colorado marathon is best for a first-timer?

The Colfax Marathon is the friendliest debut — a city course with crowd support, a festival atmosphere and an out-and-back layout that's easy to spectate and crew. The Colorado Marathon is also beginner-friendly thanks to its downhill profile, though canyon descents pound the quads, so build in some downhill training. Save the Pikes Peak Marathon for after you have mountain and altitude experience.

Is there a half marathon in Colorado if a full feels like too much?

Yes. The major Colorado road events each pair their full marathon with a half on the same weekend, so you can downshift to 13.1 miles without changing your travel plans. Denver's Colfax and the Fort Collins Colorado Marathon both run popular half-marathon distances alongside the full, which is a sensible first step if you're new to altitude or to the distance.