Broken Top and the Three Sisters under the clear blue sky of late summer. From left to right we see: Tumalo Mountain, Ball Butte, Mount Bachelor, Wikiup, Spark Lake, Cow Horn Mountain, Fuji Mountain, Broken Top, No Name Lake, Tam MacArthur Rim, South Sister, Middle Sister, North Sister, Black Crater, Mount Washington, and Three Finger Jack. Deschtues National Forest, Central Oregon Cascades. Rising above the forested skyline west of Bend Oregon, the volcanic peaks of Broken Top and the Three Sisters form one of the most striking and geologically complex mountain clusters in the central Oregon Cascades. These towering remnants of volcanic activity tell a story that spans more than a million years—a record of fire, ice, collapse, and renewal that continues to shape the region’s landscape, ecology, and outdoor experiences. The Three Sisters—North, Middle, and South—are the highest peaks in the central Cascades, each exceeding 10,000 feet in elevation. Though grouped together and often spoken of as a single massif, the Three Sisters are in fact three separate stratovolcanoes, each with its own eruptive history. Broken Top, slightly east of the Sisters and lower in elevation, is an older and heavily eroded volcanic edifice that offers insight into the early phases of mountain-building in this portion of the range. The geologic foundation of this region lies in the broader Cascade Volcanic Arc, a chain of volcanoes extending from northern California to southern British Columbia. This arc has been active for more than 40 million years, the result of the Juan de Fuca tectonic plate subducting beneath the North American plate. As oceanic crust descends into the mantle, it melts and generates magma that rises to the surface, fueling repeated volcanic episodes. In the vicinity of Bend, this process has produced an especially dense cluster of volcanic peaks. Broken Top is the oldest of the high peaks in this group, with the bulk of its eruptions occurring between roughly 300,000 and 100,000 years ago. Originally a broad stratovolcano, it has been deeply dissected by glacial erosion, exposing its internal structure and offering a rare window into the inner workings of a Cascade volcano. Steep lava flows, volcanic breccia, and intrusive dikes are now visible on its flanks—features usually hidden beneath younger eruptive layers. Evidence suggests that Broken Top’s construction ended long before the last glacial maximum, allowing ice to carve deeply into its core and shape its rugged profile. To the west and north of Broken Top, the Three Sisters volcanoes record a younger and more complex history. South Sister, the tallest of the three at 10,358 feet, is also the youngest. It began forming around 50,000 years ago and erupted as recently as 2,000 years ago, producing lava domes, pyroclastic flows, and obsidian flows near its summit and flanks. Middle Sister, located just to the north, is intermediate in age and now considered inactive. North Sister is the oldest of the three, dating back more than 100,000 years, and is no longer erupting. Unlike its younger siblings, North Sister has undergone significant glacial erosion and bears little evidence of recent volcanic activity. The juxtaposition of volcanic activity and glaciation is a defining feature of the region’s geology. During the Pleistocene, multiple glacial advances carved cirques, horns, and U-shaped valleys into the flanks of these volcanoes. Today, remnant glaciers—such as Collier and Prouty—cling to the higher elevations, continually reshaping the terrain. Meltwater from these glaciers feeds creeks and alpine lakes that supply part of the Deschutes River watershed, critical to the ecology and water supply of communities downstream, including Bend. Seismic monitoring and ground deformation studies suggest that the area is not geologically dormant. South Sister, in particular, has shown signs of uplift and magmatic movement in recent decades, leading geologists to classify it as potentially active. The U.S. Geological Survey maintains an array of monitoring instruments to detect early signs of renewed volcanic unrest, though no eruptions are imminent.
For visitors, this dramatic and ever-evolving terrain offers some of the most rewarding backcountry recreation in the Pacific Northwest. The area is crisscrossed by a network of scenic trails, including sections of the Pacific Crest Trail, which skirts the western base of the Three Sisters. Popular day hikes such as Green Lakes, Tam McArthur Rim, and Moraine Lake offer panoramic views of volcanic ridgelines, glacial valleys, and wildflower meadows. More ambitious hikers and climbers can summit South Sister—accessible via a non-technical but strenuous route from Devil’s Lake trailhead—where sweeping views encompass the Cascade crest and high desert plains beyond. Broken Top also attracts hikers, backpackers, and alpine enthusiasts. The rugged interior of the collapsed caldera contains turquoise glacial tarns and fractured lava spires that feel almost otherworldly. Though no longer an active volcano, the peak’s eroded architecture and colorful rock strata make it a geologic showcase. In late summer, snowfields linger in the shaded cirques, and mountain goats are sometimes seen traversing the crags. A popular backpacking route loops around Broken Top, linking with the Green Lakes basin and offering multiple days of solitude and exploration. In winter, the high country transforms into a snow-covered wilderness, drawing backcountry skiers and snowshoers into its quiet expanses. Nordic and alpine enthusiasts from Bend take advantage of the area’s deep snowpack and varied terrain, while the lower flanks remain accessible for winter hiking. Throughout the year, the interplay of elevation, weather, and topography ensures a dynamic environment for outdoor recreation and scientific study alike. From the pumice plains and lava flows that surround Bend to the jagged spires of Broken Top and the glacier-draped flanks of the Three Sisters, this landscape reflects the deep interplay of fire, ice, and time. For hikers, climbers, geologists, and photographers, it offers both a destination and a living archive—where every trail crosses a story still unfolding beneath the Cascadian sky.
Broken Top, Deschutes County, Deschutes National Forest, Mount Bachelor, Tam MacArthur Rim, The Three Sisters
