8 very adventurous loop runs & hikes in the Colorado Rockies

For the first time since 2013, this year I didn’t race and I won’t log at least 3,000 miles. Nagging injuries, lack of race entry luck, and a growing guiding program all played a role, as did an absence of desire — whatever I’d been running towards in my mid-30’s, I felt like I’d reached it.

Somewhat ironically, however, this year had a disproportionate share of favorite and memorable trail runs — out of my all-time Top 10-ish, this year scored five, which on this page I’ll highlight (and recommend three more). Since I wasn’t on a strict training plan or beat up from the last race, I was free to run where, when, and how far I pleased, and to do it at whatever pace felt right.

The commonality: Pfiffner Traverse

Due to their proximity and quality, I focused my efforts on Rocky Mountain National Park and the Indian Peaks Wilderness, both in the Colorado Front Range. From Boulder, the east-side trailheads are about an hour away; the west side trailheads are 2.5 hours, but conveniently my work put me in Grand Lake for a few September days.

Intentionally, these five loops included sections of the Pfiffner Traverse, which is a 76-mile high route that parallels the geographic Continental Divide between Milner Pass (on Trail Ridge Road in Rocky) and Berthoud Pass (on US-40 near the boundary of the James Peak Wilderness). The route is 40 percent off-trail, gains or loses 750 vertical feet per mile, and approaches Class 3 in difficulty. Four of the eight loops on this page are recommended section-hikes.

By including sections of the Pfiffner, I was able to edit my Pfiffner Traverse Guide, gather data for a potential FKT attempt, and elevate the difficulty of each outing, making them true adventure runs. But most importantly, the Pfiffner helped to create loops in a range that otherwise has very few.

1. Across Onahu



17.2 miles (3.5 miles off-trail) with 5,000 feet of gain+6.8 miles on Trail Ridge Road if you don’t shuttleStrava (with Tonahutu TH finish)

The heart of this run is between Timber Lake and Haynach Lakes, which are separated by two 11,800-foot passes that provide access to and out of upper Onahu Creek. Onahu is a gem: it’s one of just two trail-less valleys on the west side of the park, features a rarely visited alpine lake, and serves as a quiet refuge for elk and moose.

Several options exist for reaching and returning from Timber Lake and Haynach Lakes. A shuttle or hitch is necessary for all of them.

The shortest variation of this run starts at Timber Lake Trailhead and finishes at Green Mountain Trailhead, which are separated by seven miles along Trail Ridge Road. Alternatively, start at Milner Pass (which is about the same distance but has less climbing) and/or finish at North Inlet Trailhead (+2.4 miles). The net vertical uphill/downhill difference between running northbound and southbound is generally negligible, unless you start at Milner Pass.

Timber Lake, as seen from Timber Lake Pass, looking north







2. Continental Divide Trail Loop



25.8 miles (no off-trail) with 4,400 feet of gainStrava

The west side of Rocky Mountain National Park has just one all-trail loop — this one. Because of that, it’s already popular with backpackers and trail runners, and is actually the only route on this page with an established FKT (4 hrs 2 min), at least currently.

Start at the North Inlet/Tonahutu Creek Trailhead, and pick a direction. I prefer clockwise, so that the flat and boring 5.5-mile section along Big Meadows is at the start. If you have access to a shuttle or are willing to hitch, you can shortcut the route by 2.4 miles by starting or ending at Green Mountain Trailhead. Climb steadily to Ptarmigan Point (elev. 12,200+) and then descend into North Inlet and back to the trailhead.

A herd of cow elk at Sprague Pass, just off the Continental Divide Trail







3. North & East Inlets



21.3 miles (3.3 miles off-trail) with 6,100 feet of gain+1.4 miles without shuttle between North Inlet TH and East Inlet THStrava

The North Inlet and adjacent East Inlet both drain into Grand Lake, the largest natural lake in Colorado. Hiking trails go far up both valleys, but strangely do not connect. Fortuitously, however, they are separated by just 3.3 miles of off-trail travel, most of it Sound of Music quality.

I strongly recommend running this loop clockwise, entering the park from North Inlet Trailhead and exiting at East Inlet Trailhead, so that you have gravity on your side for the light bushwhacking between Beak Pass and Spirit Lake.

The trailheads are separated by 1.4 road miles, which can be used as a warm-up or skipped with a shuttle or hitch.

Run up North Inlet, and take a right/south turn towards Lake Nokoni and Lake Nanita. When this trail terminates at the latter lake, follow the Pfiffner Traverse to Spirit Lake, where you will intersect an unmaintained use trail. Turn right/west and follow this track to the mapped end of the East Inlet Trail, which will take you back to the trailhead.

Wildflowers and Ptarmigan Mountain







4. Triple Bypass



23.3 miles (3.1 miles off-trail) with 7,500 feet of gainStrava

The popularity of the 28-mile Pawnee-Buchanan Loop (aka Double Bypass Loop) is nearly on par with the famed Aspen Four Pass Loop. It gains 8,000 vertical feet and crosses two 12,000-foot passes on the Continental Divide, making it a fantastic long run or weekend backpack trip.

Triple Bypass is an adventurous play on this Colorado classic. Whereas the original loop drops to the 8,800-foot junction of the Buchanan Pass Trail and Cascade Creek Trail above Monarch Lake, the Pfiffner Traverse is used to “shortcut” up Thunderbolt Creek, adding three off-trail miles and a third high point, Paiute Pass.

This loop can be run in either direction, starting and ending at Brainard Lake. But by doing it counterclockwise, you can follow the guidebook description through this complicated valley and over this Class 3 pass.

Thunderbolt Creek, as seen from the Ooh La La Extra Credit route, north of Buchanan Creek. Paiute Pass is at the head of the valley and is still snow-covered.







5. Boulder Watershed



33.6 miles (4.7 miles off-trail) with 11,200 feet of gain+4.3 miles on gravel road without shuttleStrava

The Northeast Gully is the easiest non-trail exit from the iconic Lone Eagle Cirque. But it’s the most difficult feature on the Pfiffner Traverse: it’s filled with snow through midsummer, covered in loose rock and dirt in late-summer, and always steep. Before this fall’s first snowstorm, I wanted to get on this section of the Pfiffner (again), which connects Crater Lake with Coyote Park in upper Arapaho Creek.

Loops out of Monarch Lake would have been shorter (refer to the next recommended loop), but I figured that encircling the City of Boulder Watershed wouldn’t take me much longer after accounting for drive times. Plus, an end-of-season big hurrah was appealing. YMMV.

Start or finish at Rainbow Lakes Trailhead, and ideally hitch or shuttle the five miles of gravel between it and the Sourdough Trailhead, just off the Peak to Peak Highway. The loop can be done in both directions, with a slight advantage for counterclockwise (so that you can more easily follow the guidebook out of the Lone Eagle Cirque).

From Sourdough Trailhead, run/hike:

Over Niwot Ridge to Brainard Lake, Over Pawnee Pass to Cascade Creek Trail, Over Northeast Gully to upper Arapaho Creek, Over Arapaho Pass to the Fourth of July Mine, and Over the east ridge of Arapaho Peak, past the Arapaho Glacier, back to Rainbow Lakes.



The Lost Tribe Lakes basin, as seen from its western edge at the top of the elk trail.







6. Monarch Lake Loops



Min: 16.0 miles (3.1 miles off-trail) with 4,800 feet of gainMax: 32.3 miles (10.4 miles off-trail) with 11,600 of gain

Monarch Lake is the western gateway to the Indian Peaks Wilderness, and sits at the confluence of four major creeks that flow off the Continental Divide: Hell Canyon, Buchanan Creek, Cascade Creek, and Arapaho Creek.

The Pfiffner Traverse connects these drainages, using Cooper Peak Pass, Paiute Pass, and the Northeast Gully. This area has at least seven loop opportunities — each includes one pass, two adjacent passes, or all three passes. Select the itinerary that best suits your fitness, interests, and off-trail skills.

A carpet of avalanche lilies in upper Hell Canyon







7. Middle Boulder Creek



25.1 miles (4.3 miles off-trail) with 7,400 feet of gainStrava

From Boulder, Hessie Trailhead provides the quickest access into the Indian Peaks. Its popularity is proportional to its convenience, however, so the county operates a free shuttle bus on weekends to relieve parking pressure. By taking the N bus from downtown Boulder, this loop can be completed without a personal vehicle.

Go counterclockwise, so that you pass through the lowest and most heavily trafficked sections first, and reserve the wildest bit for the third quarter. The highlight is between Arapaho Pass and Rollins Pass, when this loop overlaps with the Pfiffner and mostly stays atop the Continental Divide

Looking north over Arapaho Pass and Lake Dorothy towards Apache Peak, Lost Tribe Lakes, and the west ridge of Lone Eagle Cirque







8. James Peak Skyline



17.6 miles (5.2 miles off-trail) with 6,550 feet of gain

If I’d had one more week of cooperative weather, this would’ve been the one. Years ago I completed it as an overnight backpacking trip, and was surprised that it’s not a classic, especially given its accessibility from Denver.

Start at St. Marys Glacier Trailhead ($5/day parking fee) and run clockwise, so that you finish with the best stuff. The exception: if there is a chance of thunderstorms and if you’re getting a late start, go counterclockwise so that you can get off the Divide earlier in the day.

From the parking area, cut through Alice and join the Continental Divide Trail (CDT) where it crosses the 4WD road to Loch Lomond. Follow it to Mt. Flora, the first of five 13’ers on this route.

Run/hike north atop the geographic Continental Divide, usually off-trail but sometimes with the help of a use trail, to James Peak, the final high point. Descend south on the CDT until it crosses the James Peak Wilderness Area boundary. There, travel eastward off-trail until funneling into the St. Marys Glacier. Return to your car on overused tourist trails.

James Peak, one of five 13’ers on the route. Immediately to the north it gets easier for a while, with pleasant ridge-walking atop the Divide, overlooking deep cirques to the east.



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Have questions about any of these loops?If you’ve done one, what was your experience?

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