Mount St. Helens, shown above, and at least six other volcanoes in the Cascade Range have erupted at least once during historical time. Most of the Cascade volcanic areas contain fumaroles, hot springs, or other evidence of subsurface volcanic heat, but only Mount St. Helens and Lassen Peak have erupted within the past century. USGS photo.
Location map of Cascades volcanoes and volcanic platform. Major volcanic centers are Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, Mount Adams, Mount Hood, Mount Jefferson, Three Sisters, Newberry Caldera, Crater Lake (Mount Mazama), Medicine Lake, Mount Shasta, and Lassen Peak. Click to enlarge.