Mammoth Pass to Thousand Island Lake (via JMT)

This 42.2 mile rewarding out-and-back begins at the Mammoth Pass Trailhead and travels deep into the heart of the Ansel Adams Wilderness via the John Muir Trail. With varied terrain, expansive views, and a stunning destination at Thousand Island Lake, this route offers a challenging yet accessible multi-day trip for intermediate to experienced backpackers. 

Begin your journey from the Mammoth Pass Trailhead, climbing steadily through pine forest to cross over Mammoth Pass. You'll drop down toward Red’s Meadow, where you can stop for a quick snack or resupply if needed.

From Red’s Meadow, head north on the John Muir Trail. The trail gradually climbs as it traces the Middle Fork of the San Joaquin River, weaving through shady forest, open meadows, and granite-strewn benches. You'll pass familiar landmarks like Minaret Falls, Trinity Lakes, and Shadow Lake, with numerous side trails offering opportunities to explore lakes and scenic overlooks.

Eventually, you’ll reach the junction leading to Thousand Island Lake—arguably one of the most iconic alpine lakes in the Eastern Sierra. Bordered by Banner Peak and dotted with tiny islets, the lake is an ideal spot for camping, photos, or a frigid swim if you're feeling brave.

After soaking in the views and rest, retrace your steps back to Mammoth Pass to complete the trip.

Flora and Fauna
The trail passes through montane and subalpine ecosystems, transitioning from red fir and lodgepole forests to open meadows and granite basins. Wildflowers like lupine, paintbrush, and monkeyflower bloom mid-summer, while marmots, pika, and mule deer are commonly seen along the trail. Bears are active in this area, especially around Thousand Island Lake—proper food storage is required.

Permits
Wilderness permits are required for overnight travel in the Ansel Adams Wilderness. Bear canisters are mandatory and strictly enforced. Permits can be reserved through www.recreation.gov.

Considerations
This route gains significant elevation and includes stretches above 10,000 feet. Acclimate accordingly and be prepared for afternoon thunderstorms in summer months. Water is plentiful along the route, but always treat before drinking. Snow may linger on shaded sections well into early summer.