Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In


Rocky Mountain National Park

Rocky Mountain National Park: Thunder Lake to Lion Lake Loop

Find unusual solitude at this popular alpine park on a 16.4-mile peakbagging overnight to the Continental Divide.

Get full access to Outside Learn, our online education hub featuring in-depth fitness, nutrition, and adventure courses and more than 2,000 instructional videos when you sign up for Outside+ Sign up for Outside+ today.

By high summer, most climbs in Rocky Mountain National Park start with long pre-dawn approaches to ensure a return to the trailhead by 12 p.m. and thus avoid afternoon storms. But Wild Basin offers a different look for backpackers. Camp in the designated site at Thunder Lake and get right to the climbing the next morning on this 16.4-mile lollipop loop in the park’s southern section.

From the trailhead, pass wildflower-filled meadows on the way to Thunder Lake. Scramble up scree and talus past lakes and waterfalls to the Boulder-Grand Pass, a smooth point in an otherwise rough ridge. The Continental Divide affords big-time views of Chiefshead and Mt. Meeker to the northeast. Ascend to the summit of Mt. Alice and take in the diving board view over Wild Basin, with 14,259-foot Longs Peak looming over the ridge to the northeast.

Descend carefully along the hourglass ridge. Minimize your exposure by hugging the northern side, away from the precipitous southern edge. Follow the ridge back down toward the trio of sapphire lakes pooling below the divide, and pick up the trail again at Lion Lake 1. Hike east and south to close the lollipop and end at Wild Basin.

INFO For information on permits, current trail and camp conditions, and wilderness guidelines, go to

PERMIT A wilderness permit is required for all overnight camping in the backcountry. Reservations accepted ($20 administrative fee for permits during peak season).

CONTACT Rocky Mountain National Park, (970) 586-1206;

Trail Facts

  • Distance: 26.4



Location: 40.208505, -105.565478

Thunder Lake trailhead


Location: 40.203621, -105.608313

Stay straight. Bluebird Lake Trail departs to the left.


Location: 40.213558, -105.623679

Outbound: Fork left and stay on the Thunder Lake Trail. Inbound: Continue straight. Peakbaggers attempting Mt. Alice typically head northwest on the Lion Lakes Trail, which offers a slightly shorter summit out-and-back.


Location: 40.222306, -105.645126

Campsites and patrol cabin. Camp here and curve north around Thunder Lake next day, en route to Boulder-Grand Pass.


Location: 40.224602, -105.669126

Reach Boulder-Grand Pass after a steep climb over sometimes loose rock. If hiking with a group, switchback and gather at the ends before heading back across the face. This technique reduces the chance of accidental rockfalls.


Location: 40.239273, -105.663803

13,310-foot Mt. Alice with views of Chiefshead and Longs Peak. Continue north along the class 3, hourglass ridge.


Location: 40.244977, -105.660414

Turn south and follow the ridge back toward Snowbank Lake.


Location: 40.230431, -105.638785

Reach Lion Lake 1 after passing Lion Lake 2 and numerous cascades. The meadows around here burst with wildflowers in July and August. Follow the Lion Lakes Trail south from here.

How to Pack for Backcountry Skiing

Get to know the winter safety gear you need in your pack.