⏵ Course guide · Fort Collins trail classic
The Blue Sky Marathon & Half runs between Horsetooth Mountain Park and the Devil's Backbone Open Space along Fort Collins' Front Range hogbacks, 3,500 feet of gain over 26.7 marathon miles on mostly dirt singletrack. I will walk you through the course and aid station structure first, then give you a pacing and fueling plan built for a generous, well-supported trail classic. There are free calculators along the way to dial in your own numbers.
These facts come from the official Gnar Runners event page. Check the current year details, cutoffs, and aid stations before you commit. Race logistics change year to year.
Blue Sky runs a north-south tour between Horsetooth Mountain Park and the Devil's Backbone Open Space, on the distinctive redstone hardpack of the Blue Sky Trail itself.
The course is 100% dirt and 90% singletrack, ranging from smooth dirt trail to technical rock gardens, with a small portion of dirt road and gravel trail thrown in. The marathon adds a rocky, technical stretch through the Indian Summer South and Hunter Loop section that the half marathon does not touch.
Gnar Runners publishes exact mile splits, gain, and descent for every marathon aid station: Towers (mile 4.4), Blue Sky Start/Finish (mile 9.2), Indian Summer North (mile 13.2), Indian Summer South (mile 15.6), Hunter Turnaround (mile 17.9), back through Indian Summer South (mile 20.3) and North (mile 22.7), to the finish (mile 26.7). That level of detail means you can plan your race almost turn by turn.
Marathon runners cannot receive crew assistance outside the Blue Sky Start/Finish area at mile 9.2, and pacing is not permitted for either distance. Plan your race as a solo effort between the designated support points.
With exact mile, gain, and descent numbers published for every marathon aid station, you have unusually precise data to build a real pacing plan against.
10:00 AM at Blue Sky Aid (mile 9.2), 12:30 PM at Indian Summer South outbound (mile 15.6), and 1:45 PM at Indian Summer South inbound (mile 20.3) give you three real data points before the 4:00 PM finish cutoff. A grade-adjusted pace target for the technical Hunter Loop section, the toughest stretch on the course, helps you hold honest splits through each checkpoint.
The stretch from Indian Summer South Aid through the Hunter Turnaround and back is the most rocky and technical part of the marathon. Run the earlier, smoother miles on the Blue Sky Trail itself at honest effort so you have legs left for that section rather than legs already spent.
⏵ Free tools to pace this course
With frequent, fully stocked aid stations and a generous 9 hour cutoff, Blue Sky gives you real room to dial in a standard trail marathon fueling plan.
Aim for roughly 60 to 90 grams of carbohydrate per hour, and sodium in the 300 to 700 mg per liter range. Aid stations stock Gnarly Nutrition Fuel2O, Hammer Gels, water, soda, and a range of salty and sweet bites, with GF and vegan options available on request, so lean on that support between your own carried nutrition.
Gnar Runners deliberately does not stock salt pills at aid stations, relying instead on electrolyte drink mix and salty real food. If concentrated salt caps are part of your usual plan, carry them yourself.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a Front Range October day with the free ultra fueling calculator. Browse the rest of the free running tools at the tools hub.
⏵ Train for it with Summit Line
Get a race-day plan built around YOUR fitness, this Blue Sky Trail climbing profile, and your projected splits. Summit Line reads your real training, builds a plan for the technical Hunter Loop section, and rehearses your fueling so race day is something you execute, not guess at.
The marathon climbs 3,500 feet over 26.7 miles, mostly on dirt singletrack with a rocky, technical stretch through the Devil's Backbone side of the course. Gnar Runners describes it as "designed to appeal to both veteran trail runners and those looking to experience their first trail racing adventure," backed by a 9 hour cutoff that gives most finishers real room. It is a serious trail marathon, but a genuinely approachable one by ultra-adjacent standards.
The marathon gains 3,500 feet over 26.7 miles, and the half marathon gains 1,800 feet over 13.4 miles. Course elevation ranges from 5,300 to 6,500 feet along the easternmost hogbacks of the Front Range. The published aid station table breaks the marathon climbing into clear segments, so you can see exactly where the steepest sections fall.
Mid-October in Fort Collins is usually mild but can vary, and marathon runners are on course up to 9 hours. Aid stations offer Gnarly Nutrition Fuel2O sports drink, Hammer Gels, water, soda, and a mix of salty and sweet bites, with GF/vegan alternatives available on request. Aim for roughly 60 to 90 grams of carbohydrate per hour, and sodium in the 300 to 700 mg per liter range, noting that Gnar Runners does not stock salt pills at aid stations, so bring your own if you use them. Build your numbers with the free ultra fueling calculator before race day.
The marathon has a 9 hour overall cutoff with three intermediate checkpoints: 10:00 AM at Blue Sky Aid (mile 9.2, 3 hours in), 12:30 PM at Indian Summer South outbound (mile 15.6, 5.5 hours in), and 1:45 PM at Indian Summer South inbound (mile 20.3, 6.75 hours in), before a 4:00 PM finish cutoff. The half marathon has a straightforward 6 hour cutoff with no intermediate checkpoints.
The course runs between Horsetooth Mountain Park and the Devil's Backbone Open Space, along the easternmost hogbacks of Northern Colorado's Front Range. It is 100% dirt and 90% singletrack, ranging from smooth dirt trail to technical rock gardens, with a short stretch of dirt road and gravel trail. The marathon's Hunter Loop turnaround section, past the Indian Summer South aid station, is the most rocky and technical part of the course.
Yes. Gnar Runners built this course to appeal to first-time trail racers as much as veterans, with generous cutoffs (9 hours for the marathon, 6 for the half), well-stocked aid stations every few miles, and a moderate elevation profile compared to true mountain ultras. The rocky Hunter Loop section still demands real trail-running competence, so do not treat it as road-marathon-easy, but it is a fair and honest first trail marathon.
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<a href="https://runsummitline.com/guides/blue-sky-marathon">The Blue Sky Marathon & Half course guide</a>This guide is independent and for planning only. The course details, dates, cutoffs, and aid stations come from public sources and can change year to year, so confirm the current specifics with the official race before you register or run. The fueling and pacing advice is general and not medical advice.