According to the National Park Service, describing the Sheep Rock Unit at John Day Fossil Beds National Monument:
The predominant exposures of green rock seen on Sheep Rock are a multitude of reworked layers of volcanic ash. The rich green color of the claystone was caused by chemical weathering of a mineral called celadonite. This happened millions of years ago as water moved through the alkaline ash beds under high pressure.
(click on any image for a slideshow… or see previous post for a more general view of the location.)
Wilderness is not a luxury but a necessity of the human spirit, and as vital to our lives as water and good bread. A civilization which destroys what little remains of the wild, the spare, the original, is cutting itself off from its origins and betraying the principle of civilization itself.
― Edward Abbey, Desert Solitaire