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 name is derived from the tall, straight sides that resemble the palisades of a fort. 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. William Sullivan, an early settler in the area, named Fort Rock in 1873 while searching for lost cattle.
The above is from wikipedia.org
These two photos below are from Google to show what the entire structure of Fort Rock is.
Below are photos I took at Fort Rock in 2015
Fort Rock is an amazing place to visit as is the TheFort Rock Homestead Museum near by.
Here is a link and my photos will be up in a day or so.