Union Peak is a heavily eroded shield volcano in the Cascade Range of central Oregon, located along the Cascade Crest less than 7 miles (11.3 km) southwest of the rim of Crater Lake. Ice Age glaciers eroded away most of the flanks of the volcano, leaving numerous deep cirques surrounding a central glacial horn. This is the same process that formed the summit horns of Three Fingered Jack, Mount Washington, Howlock Mountain, and Mount Thielsen from other shield volcanoes farther north in the Oregon Cascades.