Flattop Mountain to Andrews Glacier traverse

Longs, McHenry, Taylor from Hallett Peak

14 miles loop, 3500 feet elevation gain
Difficulty: Strenuous, involves an off-trail route-finding and a hazardous traverse of an active glacier and heavy physical exertion at 12,000 feet above sea level.
Access: Paved road to trailhead; $20 Rocky Mountain National Park entrance fee

Autumn aspens, a waterfall, three alpine lakes, two glaciers, and two imposing summits along the Continental Divide: such a list would be an impressive resume for a week-long backpacking trip, but the spectacular Flattop Mountain to Andrews Glacier traverse (actually a loop) in Colorado's Rocky Mountain National Park packs all of these into a day's journey. The hike starts from Bear Lake, one of the park's most visited attractions, and ascends to the Continental Divide via the Flattop Mountain Trail. From the summit of Flattop Mountain, off-trail travel leads to the summit of imposing Hallett Peak and over to Andrews Pass. Andrews Glacier provides a spectacular though slightly treacherous descent down one of the larger active glaciers in the park to a valley of lakes, meadows, and forests.

I found this hike to be exhilarating. However, this is an extremely strenuous hike that is not recommended for anyone who lacks experience with long distances, significant wind exposure, off-trail route-finding, rock scrambling, and glacier travel. Hiking poles and traction devices are more or less essential for this hike: I crossed the Andrews Glacier with poles but no traction devices and highly regretted not bringing microspikes. Winds along this hike were extreme: I experienced gale force winds consistently above the tree line on the Continental Divide. Hikers who lack glacier experience but are familiar with off-trail route-finding can visit the summit of Hallett; hikers who lack both should stick to the Flattop Mountain Trail. Sufficient acclimatization is also important: the hike tops out at the summit of 12,720-foot Hallett Peak, an elevation high enough that altitude sickness is a real problem. Air pressure is low enough atop Hallett Peak that with each breath, you would inhale only two-thirds of the oxygen that you would at sea level.

I did this hike on the first day of autumn. I woke up to perfectly blue skies at the Moraine Park Campground, where I was staying, and quickly had breakfast and made the 20-minute drive to the trailhead. From the campground, the Bear Lake Trailhead can be accessed by driving the Bear Lake Road to its terminus; visitors coming from outside the park should look up directions from their starting point. I would recommend staying nearby, though: this hike took me 10 hours to complete and I felt as though I rushed through the last few miles, so you'll want as much daylight as you can get.

From the huge parking lot at Bear Lake, I followed the wide trail towards Bear Lake and Flattop Mountain, which immediately brought me to the shores of Bear Lake. Hallett Peak, one of my destinations for the day, rose above the lake and its shores lined with pine and aspen.

Bear Lake

I followed the right fork at the Bear Lake Loop junction, taking the loop counterclockwise in the direction of Flattop Mountain and Bierstadt Lake. After a short stretch of flat, wide trail following the lakeshore, I came to a junction with the trail towards Flattop Mountain and Bierstadt Lake; I took this fork, which branched off to the right and began to ascend. The next few hundred meters were brilliantly decorated with aspens lit brightly by the morning sun. Late September, it appears, is peak time for aspen color in the Colorado Rockies, something that I didn't initially realize when I booked my trip.

Aspen color near Bear Lake

After passing a few groves of aspens, the the trail delved back into the pine forest and in a few hundred more meters came to a junction with the trail to Flattop Mountain and Bierstadt Lake. The right fork led towards Bierstadt Lake; I took the left fork, which led towards Flattop. The trail began a steady but not terribly steep climb through the forest along a flat ridge that ran north of Bear Lake. About a mile in, the trail passed another junction for a turnoff towards Lake Helene and Cub Lake; here, I again took the left fork, which kept me on the path towards Flattop.

The ensuing section of trail through the forest was fairly uneventful: I followed the switchbacks up Flattop Mountain through the forest, with fairly few views. I had plenty of company: Flattop Mountain is the easiest access to the Continental Divide in the park after the road access at Milner Pass on Trail Ridge Road, so it is an understandably popular destination. After slogging up many forested switchbacks, the trees began to thin out. I came to a viewpoint of Dream Lake, which at this point was over a thousand feet below in Tyndall Gorge. Past the Dream Lake viewpoint, the trail came out into the alpine, with the remaining trees shaped into gnarled krummholz by the relentless wind. Here, the views became superb: I could look back to the east and see Bierstadt and Sprague Lakes and the smaller peaks of the park.

View towards Bierstadt Lake, Sprague Lake, and the foothills of the Rockies

Continuing on switchbacks through the tundra, the views only improved: Longs Peak, the sentinel of the Front Range and the tallest peak and only fourteener of the park, towered over Mills Lake and Glacier Gorge to the south. The barren brown slopes of the Mummy Range appeared to the north, as did the flat ridge of Trail Ridge Road.

Mummy Range views during the ascent up Flattop

A few switchbacks later, I came to a remarkable viewpoint over Emerald Lake. The lake glistened below, the sun's rays reflecting off the surface of the lake. The steep walls of Tyndall Gorge rose around it, with Hallett Peak and Flattop Mountain rising imposingly over the head of the canyon. The Diamond of Longs Peak towered off in the distance. Everywhere I looked, there were sheer walls and craggy rock.

Longs Peak; Emerald Lake nestled in Tyndall Gorge

The views weren't the only things becoming more incredible: the wind became stronger and stronger as well as I ascended towards the Continental Divide. As the switchbacks on the trail ended, giving way to a more straightforward ascent up the (comparatively) gentle slope of Flattop, the winds became almost unbearable. Ascending from the east meant hiking directly into the wind. A sustained gale whipped down the mountain, beating down at me and forcing me to rest often and seek shelter behind protruding rocks.

The elevation also started to get to me. At 12,000 feet, I found frequently found myself out of breath even after just a few steps uphill. When I saw a small windbreaking rock shelter jut short of the summit of Flattop, I paused for a long while not just to reduce my exposure to the wind, but also to recover from altitude-induced physiological changes.

A final push put me atop Flattop Mountain, about 4.5 miles and nearly three hours of climbing away from Bear Lake. Flattop is indeed flat: the summit is almost Iowa and it is nearly impossible to tell where the true high point lies. I rested near some rocks not far from the trail junction sign that I took to indicate the true summit. The view was actually less impressive than you would have expected for a spot on the Continental Divide: the flatness and broadness of the summit cuts out much of the view in each direction. The pyramidal summit of Hallett Peak did appear quite impressive just to the south.

Flattop Mountain, aptly named

The summit of Flattop is a good stopping point for those without off-trail experience.

I left the official trail at the summit of Flattop and began to follow a somewhat well-traveled path that led towards Hallett Peak. The path was decently well marked with cairns and stuck to the flat west slope of the mountain about fifty meters or so shy of the rim of Tyndall Gorge. Wanting to check out the view of the gorge, I left the trail when it was close to the gorge rim and walked over to the actual edge of the gorge. This spot was roughly at what could be considered the saddle between Flattop and Hallett- though it isn't much of a saddle as it is barely lower than the summit of Flattop.

From the edge of the gorge, there was an excellent view of Hallett Peak and the small, steep Tyndall Glacier that hung to its slopes. The Tyndall Glacier is one of a small number of glaciers in the park, which have been retreating rapidly. The Tyndall Glacier seemed to border on being just a permanent snowfield and just barely exhibited some glacial features: a single crevasse indicated that the ice was still massive enough to move. Looking towards the summit of Hallett, I could spot a few hikers making their way up the peak. Looking towards the east, there was a clear view down the jumbled mess of rocks that formed Tyndall Gorge. Dream Lake was visible in the forest; Emerald Lake was hidden behind the rocks of the upper part of the gorge.

Hallett Peak and Tyndall Glacier

Tyndall Gorge, view to Dream Lake

I returned to the cairn-marked route and began following it up the northwest side of Hallett Peak. The route soon headed into talus and became somewhat difficult to follow. I sometimes lost sight of the cairns; when this happened, I began scrambling up the talus in the general direction of Hallett's summit. The wind and the altitude made sure that I was cold and out of breath by the time I stumbled onto the summit. Luckily, a few wind-blocking rock shelters had been assembled, allowing me to duck behind a pile of rocks and escape the wind to eat my lunch.

I spent the next half hour on the summit, enjoying the sweeping 360-degree panorama. Hallett Park lies roughly at the center of the park and allows views of more or less the entire park. The southern view was the most dramatic: the sharp peaks of the Continental Divide and Longs Peak pierced the blue skies. To the west was the Gore Range and both Grand and Shadow Mountain Lakes; to the north, I could see the Never Summer Range, the Tyndall Glacier below, and the Mummy Range further back. The east was dotted with the small lakes on the east side of the park. Far off, the flatness of the Great Plains formed the eastern horizon.

Shadow and Grand Lakes from Hallett Peak

After lunch and many photos, I left the summit and the marked path. The next mile was entirely trail-free; I traveled cross country by navigating in the general direction of Andrews Pass, which was the second canyon heading south from Hallett Peak. I headed downhill first towards the head of Chaos Canyon, which lay directly south of Hallett. The descent was scenic, with views of Longs and Taylor Peaks, but also quite difficult: I had to scramble over many extremely rocky sections, limiting my overall travel speed to less than a mile per hour. Hikers lacking navigation skills, off-trail route-finding abilities, and experience with glacier travel should turn back at the summit of Hallett Peak towards Flattop and not attempt the descent through Andrews Pass and Andrews Glacier.

Approaching the saddle between Hallett and Otis peaks, I spotted a marmot chilling on a rock above Chaos Canyon. This was my only significant wildlife sighting on the hike.

Marmot!

A little ways past the marmot sighting, I made my way to the rim of Chaos Canyon, a wild gorge between Hallett and Otis Peaks. A sign at the rim of the canyon warned against descending, stating that the canyon was quite dangerous. Lake Haiyaha appeared at the mouth of the canyon as a sparkling sapphire jewel.

Chaos Canyon, with a view of Lake Haiyaha

From the rim of Chaos Canyon, I then headed towards Andrews Pass. Otis Peak separates Chaos Canyon from Andrews Pass and can be added to this hike for a third summit; since I was quite tired from the elevation, the scrambling, and the wind, I chose to skip it. In order to avoid an ascent of Otis Peak, I roughly followed the contour of the mountain around Otis from the rim of Chaos Canyon. This route proved to be quite rocky, but in my opinion was still the most appropriate of the possible routes to take. The elevation of both saddle points is roughly similar, so I arrived at Andrews Pass with relatively little elevation gain or loss.

Andrews Pass is a spectacular spot and marks the end of the traverse along the Continental Divide. Views from the pass to the west are good but not nearly as spectacular as those from the summit of Hallett. However, the view of Taylor Peak, which was now close by, was quite impressive, as was the view down the Andrews Glacier to Andrews Tarn and the Loch. I dropped down to just east of the pass to escape the wind and took a brief break to snack before embarking on the most treacherous leg of the hike.

Andrews Pass, looking down the glacier to Andrews Tarn

The Andrews Glacier is the second largest glacier in Rocky Mountain National Park after the Rowe Glacier in the Mummy Range. The glacier is quite active but runs down one of the gentler canyons cut into the Continental Divide, making it one of the easier routes to and from the Continental Divide. Crevasses cut through many parts of its surface, making travel on the glacier dangerous for anyone without appropriate gear and experience.

As glaciers are constantly changing, it's difficult to recommend an optimal route down the glacier. I started hiking down the glacier by following a bootpath down from a sign by the pass that advised that travel down the Andrews Glacier was only for those with proper experience. Getting onto the glacier was fairly easy for me, as there was no notable bergschrund. I began my descent down the center of the glacier but gradually cut south, meeting the lateral moraine just downhill of a set of massive crevasses. I glissaded down a stretch of dead ice at the bottom of the glacier to reach Andrews Tarn. The descent down the glacier took the good part of an hour.

Crevasse on Andrews Glacier

Massive crevasses along the south side of the Andrews Glacier

I stepped my way across some glacial alluvium and then scrambled along the south shore of Andrews Tarn to reach the downstream end of the lake, where I had a good view back up the Andrews Glacier. I also finally rejoined the trail here, ending the long off-trail segment of this hike.

Andrews Tarn and Glacier

The descent on the Andrews Glacier Trail from the tarn was very steep, very rocky, easy to lose, and generally quite difficult. The trail more or less plunges steeply a talus headwall at the head of Loch Vale to reach the meadows and forests below, requiring more scrambling the entire way. At times I found the cairns confusing to follow: it seemed for a while that the trail would head directly down into the basin at the base of the headwall, but I opted instead for the trail that continued to weave through the talus and headed east before dropping down to the forest below. The unpleasant descent was made slightly better by the good views of the Sharkstooth, a remarkable craggy spire on the east side of Taylor Peak.

The Sharkstooth, on the descent into Loch Vale

After reaching the forest, the next mile or so was a bit of a slog on a rocky, rough trail through the forest to the junction with the trail to Sky Pond. Here I turned left, following the stream further downhill through Loch Vale through a slightly nicer trail to the Loch. The Loch was a beautiful, tree-lined alpine lake surrounded by big, rocky mountains. From different viewpoints around the lake, I could see both Taylor Peak and the path of my descent down Andrews Glacier. As I was fairly tired by this point in the hike, I did minimal exploring before pressing onward, descending the good part of a mile from the lake down to the junction with the Glacier Gorge Trail.

The Loch

At the fourway intersection with the trails to Mill Lake and Lake Haiyaha, I headed straight along the trail towards the Glacier Gorge Trailhead. This trail was fairly flat and offered some nice views of the peaks and cliffs to the south. After a flat half mile, I came to another junction with a trail towards Longs Peak; here I took the left fork to continue on the trail towards the Glacier Gorge Trailhead.

This trail began descending and early on offered a viewpoint just off the trail of the valley around Bear Lake and groves of brightly colored aspens in the distance. As I descended further along the trail, I began to enter trailside groves of aspens that were brilliant when backlit by the late afternoon sun. A mile past the previous junction, I arrived at Alberta Falls, a sizable and pretty drop. Crowds of people- which had been notably absent since the summit of Flattop- reemerged here, with day trippers jostling for good viewpoints of the waterfall.

Alberta Falls

Past the waterfall, the trail featured a few more good views of the stream gorge downstream of the waterfall. The gentle descent down the wide trail continued to feature many beautifully colored aspens. Three-quarters of a mile from Alberta Falls, I came to a junction with trails leading to both the Bear Lake and Glacier Gorge Trailheads. I stayed left and headed towards Bear Lake. This trail required a final ascent along the last half-mile back to the parking area where I started.

The scenery on this hike was superb. However, finishing the whole loop and hiking the section between the summit of Flattop Mountain and Andrews Tarn requires appropriate gear and experience. Even the hike to the summit of Flattop Mountain is fairly strenuous, especially due to the high altitude. Hikers lacking experience with glacier travel or off-trail navigation can still enjoy some of the superb scenery from this route on either the moderate day hike to the Loch or the strenuous day hike to the summit of Flattop.