John Day National Monument
January 19, 2010
This photo shows the scenic Sheep Rock Unit of the John Day National Monument in central Oregon. Here you'll see striking layers of deeply eroded, red-toned claystone (featured above), steep, basalt cliffs and volcanic fragments capped by ignimbrite, which are fist sized pumice fragments. The Monument has one of the longest and most continuous records of evolutionary change and biotic relationships in North America. Evidence of ancient sea beds have been found that are approximately 100 million years old, and fossil beds (in layers of tuff) date from 6 to 54 million years in age. Much of the tuff rock contain celadonite, a greenish mineral having high silicon and iron content. More than a dozen different genera of the first horses to have evolved in North America have been discovered in the John Day Monument fossil beds. Photo taken on May 8, 2009. See also the Earth Science Picture of the Day for December 5, 2009.
Photo details: Nikon D700 camera; 20 mm f/2.8 D Nikkor Lens
John Day National Monument, Sheep Rock Unit coordinates: 44.603161, -119.620803
Earth Observatory image: John Day Fossil Beds