Trail

Thornton Lake Trail

Trail
A blue lake surrounded by forested mountains.

This is a moderately strenuous 10.4-mile roundtrip with 2,300 feet of elevation gain—all payoff for views of alpine lakes and surrounding peaks. The trail starts brushy and level for the first 2 miles, then climbs steeply through cool old-growth forest to a ridge above Thornton Lake at 4.5 miles. Hardy hikers can scramble up Trapper Peak or descend to the lake shore for up-close views. Start early and bring trekking poles—the descent is brutal on the knees.

Quick facts

Distance Miles
10.4
Route Type
Out-and-back
Difficulty Level
Moderately strenuous
Elevation Gain Feet
2300

Trail profile

Distance Miles
10.4
Route Type
Out-and-back
Difficulty Level
Moderately strenuous
Elevation Gain Feet
2300
Estimated Time
5-7 hours if you're fit; 7+ if you scramble to Trapper Peak or descend to the lake.
Trail Surface
Level and brushy for first 2 miles, then climbs through cool old-growth forest with root and rock sections.
Trail Features
  • High mountain lakes
  • Alpine peaks
  • Old-growth forest
  • Ridge views above Thornton Lake
  • Trapper Peak scramble (optional)
Trail Highlights
High mountain lakes and surrounding peaks viewed from the ridge above Thornton Lake at 4.5 miles. Optional scramble to Trapper Peak or descent to lake shore for up-close alpine scenery.

Trailhead & access

Trailhead Location
From milepost 117 on State Route 20, follow Thornton Lake Road for 5 miles to the trailhead. Road is rough—low-clearance vehicles not recommended.
Shuttle Required
0

Permits & conditions

Permits Required
Yes
Permit Details
Backcountry camping allowed in designated sites only with a backcountry permit. Get permits at https://www.nps.gov/noca/planyourvisit/permits.htm Day hiking does not require a permit.
Fees
No entrance fee for North Cascades National Park.
Trail Status
Open seasonal
Seasonal Closures
Snow typically closes this trail October through May. Check current conditions with park rangers before traveling in shoulder seasons.

Facilities & rules

Restrooms At Trailhead
0
Water Sources
Thornton Lake at 4.5 miles is the water source—filter before drinking. Otherwise, carry all water for the first leg. No reliable water sources on the first half of the trail.
Accessibility
Rooty and steep. Rough access road (high-clearance vehicle required). Level and brushy first 2 miles, then sustained elevation gain through forest. Not wheelchair or stroller accessible.

Safety & strategy

Hazards
  • Elevation gain (2,300 ft sustained)
  • Rough access road
  • Ridge exposure and drop-offs
  • Optional scrambling (Trapper Peak)
  • Bears in the area
  • Steep descent
Hazard Details
The access road is rough and not recommended for vehicles with low clearance—damage happens fast. The ridge above Thornton Lake has drop-offs requiring footing care. The optional scramble to Trapper Peak involves scramble exposure. Bears are present (maintain 100-yard distance). The descent is steep and punishing—tired legs make mistakes.
Best Season
Late May through late September (park operational season with full services).
Best Time To Visit
May through September. Start by 6am—the rough access road and elevation gain demand daylight buffer for safety and descent.
Tips Advice
  • Tighten boots for the rough road access.
  • Bring trekking poles—the descent is punishing on knees.
  • Filter water at Thornton Lake if backpacking overnight.
  • Make noise for bears (100-yard distance).
  • Check backcountry permit availability before committing.
  • Don't drive the rough road in rain—damage to undercarriage happens fast.

More details

Park Area
North Cascades National Park
Dogs Allowed
Yes, leashed dogs allowed up to the national park boundary.
Shade Level
Exposed and brushy first 2 miles (sun exposure). Shaded through old-growth forest on the climbing sections.
Map Recommended
1
Insider Tips
  • The ridge at 4.5 miles looks final but keeps going. Complete the climb for the best views.
  • Morning light hits the lake better than afternoon—shoot before noon.
  • Descent is harder than the ascent; trekking poles save knees and ankles.
  • The access road is fine in dry conditions but becomes muddy and treacherous after rain.
  • Backcountry camping spots fill early in July—permit applications should go in by May.
Family Friendly Notes
Not ideal for young children. The 2,300 ft elevation gain and rough road access create logistical challenges. Older kids (12+) with solid hiking fitness and experience on steep terrain could manage with frequent breaks. The optional scramble and ridge exposure require good footing and no fear of heights.
Nearby Facilities
Nearest services at Outdoor Recreation Information Center (visitor center hours limited to park operational season, late May–late September). No restrooms or water at trailhead beyond parking and trash receptacles.
Review Summary
Hikers report the elevation gain is relentless but rewarded by high-altitude views of alpine lakes and surrounding peaks. The rough access road and exposed ridge require commitment, but those fit enough to reach the summit call it worth every step and sore muscle.

Location

Frequently asked questions

Is this trail good for beginners?

No. At 10.4 miles with 2,300 ft elevation gain, this requires solid fitness and hiking experience. This is a moderately strenuous commitment—train on easier trails first.

Are there bears?

Yes. Maintain 100 yards distance and make noise constantly. Store food properly if backpacking overnight. This is not optional—respect the distance.

Do I need a permit?

Only for overnight backcountry camping in designated sites. Day hiking is permit-free. Get overnight permits here: https://www.nps.gov/noca/planyourvisit/permits.htm

Can I bring my dog?

Yes, on-leash up to the national park boundary. Check current regulations: https://www.nps.gov/noca/learn/management/lawsandpolicies.htm

What if my vehicle can't handle the rough road?

Don't risk it. The access road is rough and not recommended for low-clearance vehicles—damage happens fast. Use a high-clearance vehicle or skip this trail.

How much water do I need?

Minimum 2 liters for day hiking. The trail is dry until Thornton Lake at 4.5 miles—carry all water. If backpacking, filter at the lake before using.

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Sources

Editorial review: YourNPGuide Editorial Team. Information is compiled from official sources, verified traveler reviews, and editorial research; no firsthand visit is implied unless explicitly documented. Learn how YourNPGuide works.

Last updated July 2026. Report an issue.