Fort Rock is a volcanic tuff ring that stands about 200 feet above the surrounding paleolake bed. It is a near circular ring of lapilli tuff that is the result of a Surtseyan eruption 50-100 ka. Most of the larger clasts in the tuff are welded glasses and pumice
But in some places small basalt bombs are included too
Subsequent weathering by wave action created an opening on the south side of the ring, so you can hike inside the ~1 mile wide crater. Where the waves interacted with the structure, along the outside and along the cut, there is a visible bench. At other tuff rings in the area, these benches show evidence of human habitation 9-10 ka
|Bench on edge of Opening|
After Fort Rock, we cruised through the desert high plains of the Christmas Valley and into Burns, where we turned north to home. We were all ready to be home, so we didn't stop to geologize along the way, just a reason to go back and explore again.