Union Peak is a heavily eroded

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

in the

Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...

of central Oregon, located along the Cascade Crest less than southwest of the rim of Crater Lake. Ice age

glaciers A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

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 Mount Thielsen, or Big Cowhorn ( Klamath: hisc’akwaleeʔas), is an extinct shield volcano in the Oregon High Cascades, near Mount Bailey. Because eruptive activity ceased 250,000 years ago, glaciers have heavily eroded the volcano's st ...

from other shield volcanoes farther north in the Oregon Cascades. Union Peak is located within Crater Lake National Park, and the summit was used as a post for fire lookouts from the 1930s to the 1950s. A trail leads to the summit from the Pacific Crest Trail off Oregon Route 62.

References

* * * * {{Crater Lake Crater Lake National Park Shield volcanoes of the United States Subduction volcanoes Cascade Volcanoes Volcanoes of Oregon Mountains of Oregon Landmarks in Oregon Cascade Range Mountains of Klamath County, Oregon Volcanoes of Klamath County, Oregon