Union Peak, in the central Oregon Cascades within Crater Lake National Park, is a heavily eroded shield volcano whose striking form was shaped by both volcanism and Ice Age glaciation. Glaciers stripped away most of its flanks, leaving deep cirques around a central glacial horn and creating a sharper, more rugged summit than its original volcanic profile. The same process formed the horned summits of other Oregon Cascade peaks such as Three Fingered Jack, Mount Washington, and Mount Thielsen. Beyond its geologic significance, Union Peak served as a fire lookout from the 1930s to the 1950s and remains a backcountry destination valued for its dramatic landscape.