The Three Sisters are closely spaced volcanic peaks in the U.S. state of Oregon. They are part of the Cascade Volcanic Arc, a segment of the Cascade Range in western North America extending from southern British Columbia through Washington and Oregon to Northern California. Each more than in elevation, they are the third-, fourth- and fifth-highest peaks in Oregon. Located in the Three Sisters Wilderness at the boundary of Lane and Deschutes counties and the Willamette and Deschutes national forests, they are about south of the nearest town, Sisters. Diverse species of flora and fauna inhabit the area, which is subject to frequent snowfall, occasional rain, and extreme temperature variation between seasons. The mountains, particularly South Sister, are popular destinations for climbing and scrambling. Although they are often grouped together as one unit, the three mountains have their own individual geology and eruptive history. Neither nor has erupted in the last 14,000 years, and it is considered unlikely that either will ever erupt again. last erupted about 2,000 years ago and could erupt in the future, threatening life within the region. After satellite imagery detected tectonic uplift near in 2000, the United States Geological Survey improved monitoring in the immediate area. Geography The Three Sisters are at the boundary of Lane and Deschutes counties and the Willamette and Deschutes national forests in the U.S. state of Oregon, about south of the nearest town of Sisters. The three peaks are the third-, fourth-, and fifth-highest in Oregon, and contain 16 named glaciers. Their ice volume totals . The Sisters were named Faith, Hope and Charity by early colonizers, but are now known as North Sister, Middle Sister and South Sister, respectively. Wilderness The Three Sisters Wilderness covers an area of , making it the second-largest wilderness area in Oregon. Designated by the United States Congress in 1964, it borders the Mount Washington Wilderness to the north and shares its southern edge with the Waldo Lake Wilderness. The area includes of trails and many forests, lakes, waterfalls, and streams, including the source of Whychus Creek. The Three Sisters and nearby Broken Top account for about a third of the Three Sisters Wilderness, and this area is known as the Alpine Crest Region. Rising from about to in elevation, the Alpine Crest Region features the wilderness area's most-frequented glaciers, lakes, and meadows. Physical geography Weather varies greatly in the area due to the