Unbeknownst to many, there's a beautiful lake tucked into the forests on the west slopes of Mount Defiance. Thompson Lake provides a great destination for day hikers or overnighters in the Alpine Lakes Wilderness. You may even find solitude here, just off the I-90 corridor. But that solitude comes at a price.
The trail up to Mount Defiance can be trying, especially in the height of summer. Climbing moderately, and then steeply away from Mason Lake, hikers are eventually rewarded with fields full of flowers and a gorgeous panorama from the summit of Defiance. But at the end of the traverse just below the summit, a little bootpath descends quietly into the forest.
This is the trail to Thomspon Lake: a large, scenic lake with nice alpine boulder fields and great views of the interior of Alpine Lakes Wilderness and Pratt river valley. Here, a number of small forested islands catch the sunlight in morning and evening, providing a relaxing panorama if you've chosen to camp.
From the traverse on Defiance, follow the narrow, somewhat brushy trail over to the north side of Defiance Ridge. 2.6 miles of ridgeline traverse bring you to yet another backbone, where you may be able to spot Spider Lake and creek in the basin to the southeast.
But you're heading to the northwest. Thompson Lake lies at the base of several steep switchbacks, just 0.8 miles away.
The lake has some good campsites. The main area is across the inlet stream just after you cross the stream on some logs when you finally get down the switchbacks. The trail around the lake passes a junction with trail 1009A and 0.3 miles past that junction are some smaller sites.
WTA Pro Tip: Because this trail starts from the very popular Ira Spring Trailhead, consider arranging a pick up or drop-off for this hike, particularly if you're doing an overnight
Thompson Lake via Mount Defiance


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Length
- 19.8 miles, roundtrip
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Highest Point
- 4,200 feet

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Old growth
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Lakes
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Established campsites
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Waterfalls
Parking Pass/Entry Fee
Northwest Forest Pass
Unbeknownst to many, there's a beautiful lake tucked into the forests on the west slopes of Mount Defiance. Thompson Lake provides a great destination for day hikers or overnighters in the Alpine Lakes Wilderness. You may even find solitude here, just off the I-90 corridor. But that solitude comes at a price.
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Hiking Thompson Lake via Mount Defiance
WTA worked here in 2018!
Hike Description Written by
Anna Roth,
WTA Staff
Map & Directions
Before You Go
Parking Pass/Entry Fee
Northwest Forest PassWTA Pro Tip: Save a copy of our directions before you leave! App-based driving directions aren't always accurate and data connections may be unreliable as you drive to the trailhead.
Getting There
Head east on I-90. Some 44 miles west of Seattle, take Exit 45 (Forest Road 9030.) The pavement ends in a quarter mile, and beyond that there may be significant potholes. At a fork 0.8 miles from I-90 take the left branch onto Road 9031. The right branch, Road 9030, goes to the Talapus Lake trailhead. At 3.8 miles from I-90, reach the large parking area for the Ira Spring Trail (#1038.) A privy is available, but no regular water source. A Northwest Forest Pass is required.
Be aware that this is a very popular trailhead; parking can be quite crowded here on a weekend. Take heed of the No Parking areas -- the Forest Service regularly checks this area and will issue tickets for violations.
More Hike Details
Trailhead
Snoqualmie Region > Snoqualmie Pass
Thompson Lake (#1009.1), Mount Defiance (#1009), Ira Spring (#1038)
Mt. Baker-Snoqualmie National Forest, Snoqualmie Ranger District
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