4 Expert-Level Colorado Trail Running Loops

Zirkel Circle, Mount Zirkel Wilderness

Length: 10.4 miles, round-trip loop
Vertical gain: 2,360 feet
Zirkel features a perfect vantage to take in deep blue Gilpin Lake, surrounded by the Mount Zirkel Wilderness’ jagged peaks, from the trail’s high point atop Gilpin Ridge. Pro tip: The loop is more approachable if you run clockwise, so the majority of elevation gain happens over the first half of the circle. The downhill finish is especially helpful when outrunning the thunderstorms that inevitably form in the afternoons.

Venable-Comanche Loop, Sangre de Cristo Wilderness

Length: 12.2 miles, round-trip loop
Vertical gain: 3,740 feet
With a sheer drop to one side, the Phantom Terrace, an exposed section of this trail about 12,700 feet up the Sangres, will make you question your life choices.
Pro tip: Keep right on the Venable Trail just before the Phantom Terrace for an extra challenge in the form of the Rito Alto Four Pass Loop, a separate, seldom-trafficked route that adds 23 miles.

Pawnee-Buchanan Loop, Indian Peaks Wilderness

Length: 26.5 miles, round-trip loop
Vertical gain: 6,632 feet
Don’t let the unbeatable wildflower viewing lure your eyes off this rocky route for too long. The majority of the trail is above treeline, meandering by Isabelle Lake and Cascade Falls and traversing Pawnee and Buchanan passes. Pro tip: Start early. The ideal takeoff point is Brainard Lake Recreation Area’s Long Lake trailhead, where parking is limited.

Four Pass Loop, Maroon Bells–Snowmass Wilderness

Length: 27.1 miles, round-trip loop
Vertical gain: 7,265 feet
There’s no shortage of incredible vistas when you’re summiting four 12,000-plus-foot passes, but the views of Snowmass Lake—a turquoise gem at the base of Snowmass Mountain—from the top of Trail Rider Pass will take away whatever breath you have left. Pro tip: Taking the counterclockwise route (hitting Buckskin Pass first) ensures a great photo op of Snowmass Lake bathed in morning light.

Buffalo Mountain Loop, Eagles Nest Wilderness

Length: 13.4 miles
Vertical gain: 2,976 feet
Circumnavigating Buffalo Mountain counterclockwise, this loop passes Willow Creek Falls, a 500-foot gusher, and, after a steep climb up Eccles Pass, has sweeping views of the Tenmile Range and surrounding peaks. Tip: If you have the energy, add bonus miles and elevation by tagging the summit of 12,777-foot Buffalo Mountain; you’ll climb 2,969 feet over 2.4 miles on Buffalo Cabin Trail, which connects to the main route.

Note: We verified the mileages and vertical gains with land managers when possible, but these figures can vary based on where you access each trail. Research your specific intended route ahead of time; trailrunproject.com and alltrails.com are good resources.