South Sister

South Sister ranks No. 35 among the 57 ultra-prominent peaks in the contiguous United States, rising 10,363 feet in the Cascade Range of central Oregon with 5,590 feet of clean prominence. It is the highest of the Three Sisters volcanoes and Oregon's third-highest summit within the Three Sisters Wilderness. Most hikers use the South Sister Climber Trail from Devil's Lake for 13 miles round-trip with 4,950 feet of gain on Class 2 terrain. Central Cascades Wilderness permits are required June 15 through October 15 via Recreation.gov.

Geologically, South Sister is the youngest of the Three Sisters volcanoes; its most recent eruption occurred about 2,000 years ago, and the USGS has documented earthquake swarms and ground uplift southwest of the summit in recent decades. The mountain supports several glaciers, including Prouty Glacier, widely cited as Oregon's largest glacier. At the summit crater sits Teardrop Pool, commonly cited as the highest lake in Oregon. Unlike North Sister and many snowy-season routes on Middle Sister, South Sister's standard summer route is nontechnical and accessible to fit hikers in good conditions, which accounts for its status as a high-demand day-use permit in the Central Cascades Wilderness system.

South Sister Climber Trail (Devil's Lake)

The standard route departs from Devil's Lake Trailhead at approximately 5,480 feet. Trail access from the trailhead area now uses the Elk-Devils Trail highway underpass rather than a direct highway crossing; check current trailhead instructions on Recreation.gov before departure. From the trailhead, the route climbs through conifer forest for roughly two miles, gaining about 1,400 feet before the trees open onto a broad sandy volcanic plateau. Broken Top and the full south face of South Sister come into view here.

From the plateau, the trail continues northeast across open terrain past Moraine Lake junction (approximately mile 3.2, 7,400 ft) before pitching steeply toward the Lewis Glacier terminal moraine at roughly 8,900 feet. The upper mountain is direct and unrelenting, with few meaningful switchbacks and a sustained grade on loose volcanic scree that gains roughly 1,500 feet to the crater rim at approximately 10,200 feet. A short traverse right along the crater rim reaches the summit. Most parties complete the 12–13 mile round trip in 8–10 hours.

Alternative access routes include the Green Lakes Trailhead to the north, which adds mileage but draws from a separate permit quota, and Todd Lake Trailhead, also an option when Devil's Lake permits are sold out.

Key Landmarks

• Devil's Lake Trailhead (5,480 ft)
• Moraine Lake junction (7,400 ft, ~3.2 mi)
• Lewis Glacier terminal moraine (~8,900 ft, ~4.7 mi)
• Crater rim crest (~10,200 ft)
• Summit crater and true summit high point (10,363 ft)

July through September is the standard climbing season. May through June ascents may require crampons and ice axe above 8,000 feet. Afternoon convective storms are common in July and August; plan an early start and aim to clear the exposed upper mountain before early afternoon. The standard route does not require glacier travel; avoid entering glacier terrain without proper equipment and training.