 None have erupted since St. Helens, but precautions are being taken nevertheless, such as the Mount Rainier Volcano Lahar Warning System in Pierce County, Washington.The Cascade Range is made up of a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris.Rising above this volcanic platform are a few strikingly large volcanoes, like Mount St. Helens, that dominate the landscape.