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Thornton Lakes



9.5 mile 15.4 kilometer out and back
74% Runnable


Ascent: 3,067' 935 m
Descent: -3,067' -935 m
High: 5,018' 1,530 m
Low: 2,499' 762 m


Avg Grade: 12% (7°)
Max Grade: 58% (30°)


No Dogs
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Trail shared by Sarah Baker

A pleasant, steep trail through dense forest to subalpine lakes in a beautiful mountain basin.

Sarah Baker

Features Birding · Lake · River/Creek · Swimming · Views · Wildflowers · Wildlife


The Thornton Lakes Trail is a nice day trip or overnight to a subalpine lake with views of the rugged North Cascades Peaks. Additionally, there are many opportunities for off-trail exploration in the area.

The first two miles of trail gently ascend an old road grade through new growth forest. Then, the trail trail climbs steadily upwards through mature hemlock forest until it reaches meadows and attains the ridge. The ridge offers spectacular views of Triumph Peak and lower Thornton Lake.

The short, steep trail down to lower Thornton Lake is often muddy and slippery. Be especially careful on the rock and floating-log scramble to cross the outlet of the lake and reach the camp.

Need to Know

A backcountry permit is required for all overnight stays in the national park. Camping in the Thornton Lakes area must be at a designated site. Permits are limited so make sure to check with a the local Rangers Station for permit availability.

Thornton Lake has three sites which are popular and fill quickly during busy periods. Camping is not allowed on the ridge above the Thornton Lakes, Trappers Peak, or at the second Thornton Lake. Climbers attempting Triumph Peak may obtain a permit to camp at the Triumph Col cross-country zone.


The trail starts at Thornton Lakes Trailhead and follows an old road grade for 2.3 miles through a logging area from the 1960's, before the park was established. The trail is surrounded by a natural mix of Douglas-fir, Pacific silver fir, hemlock, cedar, alder, maples, and various shrubs that can prove bothersome.

At the third switchback, the trail steepens and continues to climb up many moderate to steep switchbacks. The trail ascends through forested slopes, through a wet meadow and over a creek before officially entering North Cascades National Park. At 4.5 miles, the trees thin, and the trail breaks out into meadows of heather and huckleberry and continues to climb to an open ridge. From the ridge, you get expansive views of Mt. Triumph, Teebone Ridge, and the Skagit Valley.

A scramble route leaves the main trail at the ridge and ascends steeply towards Trappers Peak. If you spend the night at Thornton Lakes, this can be a great extension of your trip. The views from Trappers Peak of the three Thornton Lakes and the rugged Picket Range are truly spectacular.

The main trail descends steeply for 0.6 miles down 500 ft along a lesser ridge with views of lower Thornton Lake and Triumph Peak beyond. Be careful crossing the lake outlet as the boulders and rocks can be wet and slippery! The maintained trail ends at lower Thornton Lake where there are 3 permit campsites and a compostable toilet.

From lower Thornton Lake there is a primitive climber's path that proceeds to the upper lakes and Triumph Col. The two lakes above are cupped in their own rocky basin, forming classic cirque lakes that were created by glaciers which carved the rock basin before retreating to where they are today.

Flora & Fauna

The trail offers a rich wildlife habitat. Keep an eye out for deer, bear, marmot, and birds. Hawks and eagles can be observed during autumn migration.

This ecosystem has very fragile vegetation. Make sure to avoid trampling vegetation by running and resting only on durable surfaces such as the trail, snow, or rocks.

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Trail Ratings

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  4.6 from 10 votes
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in Washington


34 Views Last Month
3,129 Since Mar 1, 2016



Enjoy this stellar view before descending to Thornton Lake.
Feb 6, 2017 near Diablo, WA
Looking down to Thornton Lakes.
Sep 17, 2016 near Diablo, WA
You'll have to cross this precarious log at the outlet of lower Thornton Lake.
Feb 6, 2017 near Diablo, WA
New footbridge over the creek.
Sep 17, 2016 near Diablo, WA


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