Fort Rock is a volcanic landmark called a tuff ring, located on an Ice age lake bed in north Lake County, Oregon, United States
The ring is about 4,460 feet (1,360 m) in diameter and stands about 200 feet (60 m) high above the surrounding plain. Its tall, straight sides resemble the palisades of a fort, thus giving the rock its name. The region of Fort Rock Basin contains about 40 such tuff rings and maars and is located in the Brothers Fault Zone of central Oregon’s Great Basin.
Fort Rock was created when basalt magma rose to the surface and encountered the wet muds of a lake bottom. Powered by a jet of steam, molten basalt was blown into the air, creating a fountain of hot lava particles and frothy ash. The pieces and blobs of hot lava and ash rained down around the vent and formed a saucer-shaped ring of lapilli tuff and volcanic ash sitting like an island in the lake waters. Steam explosions also loosened angular chunks of black and red lava rock comprising the valley floor.
The ring is considered a great place to hike and scramble and not far from another curious geological location known in Oregon as Hole in the Ground