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Guide to Hiking Thornton Lakes | North Cascades

The Thornton Lakes are in North Cascades National Park in Washington and accessible via a 5.2-mile trail to Lower Thornton Lake.

The gorgeous alpine lakes are just southeast of the formidable Mount Triumph and below Trapper Peak.

Make sure to check out our Complete Guide to Trapper's Peak Hike for more!

Where is Thornton Lakes?

Thronton Lakes is in North Cascades National Park, just below Trapper Peak and along the trail to reach its summit. The trailhead to reach the lakes is at the top of a long, gravel road in Ross Lake National Recreation Area.

Trailhead Coordinates: 48.65492902979536, -121.32528770629733

Directions to Thornton Lakes

Use the below map to navigate to Thornton Lakes or input the above coordinates

Need to Know

  • Dogs are not allowed past the National Park boundary.

  • There is a bathroom at the trailhead.

  • No permit is required to park at the trailhead.

  • Backcountry permits are required for camping.

  • Camping spots fill up fast.

  • The hike provides incredible views of the North Cascades

  • It's possible to see deer, marmots, and more along the trail

The best view of Thornton Lakes from above
The best view of Thornton Lakes from above

Thornton Lakes Trail

The Thornton Lakes Trail is a 10.9-mile out and back trail that ascends just over 3,000 feet to Lower Thornton Lake.


Elevation Gain​

Time Required


10.9 miles


6.5 hours


Below is a map of the hike to Thornton Lakes.

Thornton Lakes Trailhead

The trail starts in Ross Lake National Recreation Area. If driving east on Highway 20, the turn onto Thornton Lakes Road will be on your left. If you're driving west, then it will be on your right.

Less than pleasant bathroom at the Thornton Lakes Trailhead
Less than pleasant bathroom at the Thornton Lakes Trailhead

The sharp turn begins weaving uphill on a road that varies in quality depending on what time of year you're there. Be ready for potholes and some serious washboarding.

The trailhead, at about 2,600 feet in elevation, has enough space for about 20 cars. It also has a pit toilet (Pro-tip, the bathroom is less than pleasant).

Hiking the Thornton Lakes Trail

The first part of the trail is 2.3 miles long and is nearly entirely flat. It was an old logging road, so it is very evenly graded and quite wide. There are a few small stream crossings before the trail cuts to the right at about 2,700 feet and begins gently weaving uphill. The trail gains about 1,00 feet before a series of steeper switchbacks take you to your first view of the lake.

At about 4.5 miles, the trees thin, and you'll enter a meadow where huckleberries are present in peak season.

Looking out at the McMillan Spires
Looking out at the McMillan Spires

You'll see a sign directing you to Thornton Lakes; take the trail to the left and descend toward Lower Thornton Lakes for 0.6 miles and around 500 feet of elevation loss. This portion of the trail is often slippery and muddy.

This is also your high point at 5,018' if you choose not to climb up to Trapper's Peak. The Thornton Lakes Campground is right at the end of this portion of the trail. Trapper's Peak is another 0.7 miles up the main trail and is at an elevation of 5,919'.

Read out Guide to Trapper's Peak Hike for more.

If you want, there is an unmaintained trail that will take you up to the upper lakes and Triumph Col, where you can get a fantastic view of the Picket Range. The peaks around you include Pinnacle Peak (6,775'), Mount Terror (8,032'), Inspiration Peak (7,720'), and the McMillian Spires.

It is at Triumph Col that you'll camp if you're planning on climbing Mount Triumph (6,969') the next day (ropes and climbing gear required!).

Panorama at the summit of Trapper's Peak
Panorama at the summit of Trapper's Peak

Flora and Fauna Along the Way

Along the trail, you'll encounter:

  • Douglas-fir trees

  • Pacific silver fir trees

  • Hemlock trees

  • Cedar trees

  • Alder trees

  • Maple trees

It's also possible to run into marmots, birds, deer, bears, and predatory birds, like hawks and eagles. The latter is most commonly seen in autumn.

Marmot on the way to Thornton Lakes
Marmot on the way to Thornton Lakes

The ecosystem in this area is incredibly important and quite fragile. Do what you can to stay on the trail, especially in upper meadow areas, and avoid stepping on anything you don't need to.

There are three different areas to camp around Thornton Lakes, and you'll need a permit for each. A backcountry permit is required for any overnight stay in the national park. It's possible to get to the Marblemount Ranger Station the day before to pick up a permit.

The sites around the lake are flat and unmaintained. This means there are no facilities or services.

Camping is not allowed on the ridge above Thronton Lakes, on Trapper's Peak, or at the upper lakes.

Our Guide to Camping at Thornton Lake has more information.

Thornton Lakes Hiking Guide

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