November 30, 2015
Photographer: John Kupersmith
Summary Author: John Kupersmith
Shown above is a volcanic feature known as a tuff ring found in south-central Oregon. It's called Fort Rock for obvious reasons. It formed an estimated 50,000-100,000 years ago when basaltic magma pushed toward the surface and contacted the mud underlying an ancient lake bottom. The resulting ring is 200-300 ft (60-90 m) high and 4,460 ft (1,360 m) in diameter -- wide enough to fit the main span of San Francisco's Golden Gate Bridge inside. For scale note the farm buildings to the right of Fort Rock. Photo taken on July 8, 2015.
Photo Details: Fujifilm X30; ISO 100;11.7mm focal length; 1/800 sec. exposure; f/4.5.