Mount Thielsen, Oregon

Mount Thielsen (9,182 feet, 2,799 meters) is a shield volcano comprising approximately 2 cubic miles (8 cubic kilometers) of basaltic andesite built atop a broad pedestal of older lava. Thielsen is remarkable even at a distance for its colorfully interbedded pyroclastic rocks that dip away from the jagged spire of the central plug, often called the "lightning rod of the Cascades". The most spectacular views are on the north and east sides (accessible only by foot or horseback) where now-vanished glaciers have carved precipitous cirque walls that reveal the construction. Thielsen's age is approximately 290,000 years, and its geomorphology is a reference point for assigning Cascade Range volcanoes to the age division 0-0.25 million years (younger than Thielsen) or 0.25-0.73 million years (older than Thielsen).