South Sister is the highest of the Three Sisters volcanic trio and the third-highest summit in Oregon. It rises to 10,363 feet above the conifer forests of the Deschutes National Forest. Its roughly 5,590 feet of topographic prominence make it one of Oregon's most prominent Cascade summits, and the mountain stands as the dominant summit of the Three Sisters Wilderness, a nearly 286,000-acre roadless area straddling the Deschutes and Willamette national forests. Geologically, South Sister is the youngest of the three 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, though this has not indicated an imminent eruptive threat.
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 one of the most sought-after day-use permits in the Central Cascades Wilderness system.
Recommended Route
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)
warning The upper mountain above treeline is fully exposed. Afternoon convective storms are common around South Sister from July through August. Most experienced parties aim to reach the summit by midday and clear the crater rim by early afternoon to stay ahead of lightning risk.
Permits & Camping
Climbing Permits
South Sister falls within the Central Cascades Wilderness Permit area, administered by the Deschutes National Forest. Permits are required from June 15 through October 15. Day-use permits are issued per person at $1 per person per entry; overnight permits cover groups of up to 12 at $6 per group. Permits are not available at the trailhead or at Forest Service offices; they must be reserved through Recreation.gov. Day-use permits are released in 10-day and 2-day rolling windows at 7:00 AM Pacific time daily. Overnight permit release dates and inventory distribution vary by year; Recreation.gov posts the current season's release schedule before the permit window opens. Weekday dates and shoulder-season windows in late June and early October are usually less competitive than peak summer weekends. A Northwest Forest Pass or America the Beautiful Pass is required for trailhead parking. Permit quotas, fees, and release windows can change; confirm details on Recreation.gov before planning a trip.
Camping & Wilderness
Overnight permit holders are generally not assigned designated campsites, but must follow all wilderness regulations, closure areas, group-size limits, and required setbacks from lakes, streams, and trails. Moraine Lake (approximately 7,400 ft) is the primary on-route overnight area and is managed as a designated camping basin; overnight campers must use posted sites and leave the basin if all designated sites are full. Green Lakes Basin, a viable alternative for parties approaching from the north, operates under the same designated-site rules. Campfires are prohibited above 5,700 feet; use a stove for all camps above treeline. The summit crater rim has informal rock windbreaks, but overnight camping there is exposed, environmentally fragile, and not recommended. Maximum overnight stay is 14 consecutive days. Groups of up to 12 are permitted on an overnight permit.
Wildlife & Seasonal Conditions
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.
Safety Information
Technical Requirements
- Loose Rock Scrambling
- Alpine Start
- Off-Trail Navigation
- Snow Travel
Known Hazards
- Lightning Exposure
- Loose Rock & Scree
- Rockfall
- Altitude Sickness
- Whiteout Conditions
- Hypothermia
Getting There
location_on South Sister · OR
Data source: Deschutes National Forest, Recreation.gov Central Cascades Wilderness Permit, USGS Cascades Volcano Observatory, Washington Trails Association trip reports
