I have a feeling 2026 is going to be a good year for adventures. How could it not be, when my first hike of the year took place on January 2nd, beneath a beautiful sunrise sky (photo above, and more to come), and involved the long-overdue completion of one of my many hiking-related lists?
As we all know, I have far too many lists. Most of them are so lengthy that I’m not even close to completing them. But this particular list only contained five items: Mount Sanitas, Flagstaff Mountain, Green Mountain, Bear Peak, and South Boulder Peak.
These five summits are known as the Boulder Peaks and, along with the angular rock slabs called The Flatirons, form the iconic backdrop to the town of Boulder, Colorado.
Some people – people who are far more intense than me – attempt to summit all five peaks in one 16.4 mile (26 km), 6000+ foot (1830+ m) day, a challenge that’s been dubbed the Boulder Skyline Traverse.
I’ve never attempted the challenge, nor do I have any plans to do so. But I have hiked all five peaks separately. While this post puts all these hikes together, this was actually a six year journey. I hiked the first – Bear Peak – in January 2020 and the last – Flagstaff Mountain – in January 2026.
Today I’ll be recounting each hike individually. We’ll go from north to south, shortest to tallest, as the traditional Skyline Traverse route goes.
Table of contents
Mount Sanitas
The furthest north, and also the lowest of the five summits, is Mount Sanitas. The main route for this hike begins at Centennial Trailhead on Sunshine Canyon Drive; however, there are other starting locations due to the interconnected network of trails that weave through the landscape.
The Mount Sanitas hike is most commonly completed as a loop; my friend and I took the shorter but steeper Mount Sanitas Trail up and descended via the longer but more gradual East Ridge-to-Sanitas Valley route. Either way, the elevation gain will be about 1300 feet (400 m). The main difference is that this elevation is packed into just 1.2 miles (2 km) on the Mount Sanitas trail while it’s spread out over 1.9 miles (3.1 km) on the Sanitas Valley route.
From the summit, we had views south and east over Boulder and The Flatirons, everything lush and green with the arrival of summer.
- Hike stats: 3.1 miles (5 km) with approx. 1300 feet (400 m) of elevation gain
- Summit elevation: 6863 feet (2092 m)
Flagstaff Mountain
As mentioned above, Flagstaff Mountain was my final summit. And while I felt the accomplishment of finally completing all five, in retrospect I wish I’d saved one of the peaks with better views for last.
Oh well.
The weather was unseasonably warm when my friend and I set off to summit Flagstaff on this January morning. There was no snow and the temperature was well above freezing as we stepped onto the trail at sunrise.
We parked at the base of Gregory Canyon Road and ascended via the Flagstaff Trail. In warmer weather, there is a road up Flagstaff Mountain. In winter, the upper section of the road is closed. For us, this meant there was very little traffic, which was nice because the trail crosses the road multiple times.
Flagstaff Trail doesn’t actually go to the summit of Flagstaff Mountain. Officially, no trails go to the summit of Flagstaff Mountain. But it connects to the Ute and Range View Trails, which form a loop that encircles the mountain. From here, there’s a well-established unofficial trail that branches off and leads to the top. While my friend had hiked this mountain many times before, she’d never bothered to find the actual summit. This time – for my sake – we did.
After summiting, we followed the path back to the Ute Trail, finished the loop, and retraced our steps down the Flagstaff Trail to the car.
- Hike stats: 5 miles (8 km) with 1444 feet (440 m) elevation gain
- Summit elevation: 6977 feet (2127 m)
Green Mountain
Green Mountain was my fourth summit. Though I didn’t initially set out to hike all five of these peaks with the same friend, over the years we’d hiked three of them together. By that point, we decided I should do the last two with her as well.
As with Sanitas, we hiked Green Mountain in late spring when everything was lush and green and wildflowers were everywhere. Green Mountain certainly lived up to its name. It was a hot day, but the saving grace was that much of the trail is shaded.
We did not take the typical route to the summit, opting instead to begin at Gregory Canyon Trailhead and combining the Gregory Canyon, Saddle Rock, Ranger, and Greenman Trails into a 6.1 mile (9.8 km) lollipop loop. The topography of all five Boulder Peaks is steep and, particularly in the final push to the Green Mountain summit, the trail gained a lot of elevation.
With each of these peaks being taller than the previous, the view from each summit is progressively more expansive. From the summit of Green Mountain, we could see across the Front Range, as well as the snow-capped summits of the Indian Peaks and Rocky Mountain National Park.
- Hike stats: 6.1 miles (9.8 km) with 2488 feet (758 m) of elevation gain
- Summit elevation: 7926 feet (2416 m)
Bear Peak
Bear Peak is the fourth of the five summits, and the first one I climbed. There are multiple routes up this peak as well; my husband, my friend, and I chose to begin at the National Center for Atmospheric Research (NCAR).
From the parking area, the NCAR Trail loops around the hillside and down to the Mesa Trail (meaning we’d have to climb back up this hill on the hike out…). There are a lot of forks through this first section, but all are well-marked, so as long as you have a copy of the trail map you should be okay.
After a short distance on the Mesa Trail is a Y intersection. We now had an important decision to make: which way to go?
- Fern Canyon Trail climbs to the summit in just 1.6 miles (2.6 km). In the final 1.1 miles (1.8 km), it gains 1900 feet (580 m). And no, that’s not a typo. It’s absurdly steep.
- Bear Canyon Trail heads north and connects to the West Ridge Trail, reaching the summit after a fairly leisurely 3.9 miles (6.3 km). The final section is steep, but not nearly as steep as Fern Canyon.
We opted to ascend Fern Canyon and descend via West Ridge-Bear Canyon. This is one of the most brutally steep trails I’ve ever climbed. But I think descending Fern Canyon would have been even worse. It definitely would have wrecked my knees.
I should also mention that the final short section to the summit of Bear Peak is a scramble across some haphazard slanted boulders. I didn’t have a problem with it, but my friend was a little uneasy due to the exposure. Her surprisingly agile dog made it too, but not all dogs would be able to navigate this section, so that’s something to think about when deciding whether to bring your pup.
I seem to only have 3 photos from this hike. I’ve never in my life taken only 3 photos of anything, which means I’ve either misplaced or accidentally deleted the others. Oops.
- Hike stats: 8.5 miles (13.7 km) with approx. 2800 feet (855 m) elevation gain
- Summit elevation: 8458 feet (2578 m)
South Boulder Peak
Should we have tackled this one the day we did Bear Peak? Probably. They share a saddle and the summits are only about 0.6 miles (1 km) apart. But we were exhausted and it was already a long hike so we really didn’t feel like adding another 1.2 miles (2 km) to it. Plus, at the time, I wasn’t necessarily committed to this idea of summiting all 5 peaks.
So instead, I had to re-gain all that elevation – and then some – on a separate hike. South Boulder Peak – or SoBo, as it’s often called – is the highest of the Boulder peaks.
My friend, her husband, and I took a slightly less common route to the summit of this one, as they had climbed it before and were looking to hike some new sections of trail. We began at the South Boulder Creek Trailhead, which adds a couple miles to the approach. They’re fairly flat and scenic miles along the Bluestem, South Boulder Creek, and Mesa Trails, so I didn’t really mind.
The clouds from an overnight storm lingered in the morning but progressively cleared as we climbed, and the sun was out once we reached the summit. You can see the difference in the photos below, which are from both the ascent and descent.
Eventually, we reached the dreaded Shadow Canyon Trail which – no matter your starting point – must be ascended to reach the summit from this side. This 1.3 mile (2.1 km) trail to the saddle between Bear and South Boulder Peaks gains 1600 feet (490 m) of elevation. It’s steep, rocky, and – in our case – snowy. It wasn’t quite as strenuous as Fern Canyon, but it was close.
And once we reached the top of Shadow Canyon… well, we still weren’t quite there. The final 0.25 miles (0.4 km) from the saddle to the summit gains an additional 350 feet (107 m). But we did it!
- Hike stats: 10.9 miles (17.5 km) round-trip with 3130 feet (954 m) elevation gain
- Summit elevation: 8524 feet (2598 m)
Boulder Peaks: complete ✅
The Important Stuff:
- Getting there: there are so many trailheads and intersecting trails weaving around these peaks, so there are many starting points. With that in mind, it’s important to bring a map or maps app so you can find the proper trailhead and correctly navigate each trail junction. Here is the trail map.
- Fees and passes: most Boulder OSMP trailheads charge a $5/day parking fee (follow the pay-by-phone instructions posted at each location), or you can purchase an annual parking pass.
- Other: be prepared to share these trails with plenty of people and usually quite a few dogs. Deer and, less commonly, bears and mountain lions, may be spotted while hiking, so be sure you know what to do should you encounter a wild animal.
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