The Crooked River caldera is a large and ancient

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

that straddles three central

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

counties. The diameter of the caldera is about and is notable for the

welded tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

present at Gray Butte, Smith Rock, Powell Buttes, Grizzly Mountain and

Barnes Butte Barnes Butte is a rhyolite dome of volcanic rock in Crook County, Oregon, United States located partly within the city of Prineville. Barnes Butte is composed of welded tuff and is a part of the Crooked River caldera. It was the site of a 19 ...

. The volcano is considered extinct and last erupted about 29.5 Ma.

References

{{reflist Calderas of Oregon Landforms of Jefferson County, Oregon Volcanoes of Crook County, Oregon Volcanoes of Deschutes County, Oregon Volcanoes of Oregon Oligocene calderas