The Three Sisters are volcanic peaks of the Cascade Volcanic Arc in Oregon in the northwestern United States. More than 10,000 feet (3,000 m) in elevation, they are the third-, fourth-, and fifth-highest peaks in Oregon. They are about 10 miles (16 km) south of the nearest town, Sisters, in the Three Sisters Wilderness. The three mountains, particularly South Sister, are popular destinations for climbing and scrambling. They are subject to frequent snowfall, occasional rain, and extreme temperature variation between seasons. Although they are often grouped together as a complex volcano, the three mountains differ in geology and eruptive history. Neither North Sister nor Middle Sister has erupted in the last 14,000 years. South Sister last erupted about 2,000 years ago, and there are indications it could erupt again. After satellite imagery detected tectonic uplift near South Sister in 2000, the United States Geological Survey improved monitoring in the immediate area. (Full article...)