John Day Fossil Beds National Monument is a U.S. national monument. Located within the John Day River basin and managed by the National Park Service, the park is known for its well-preserved layers of fossil plants and mammals.
The monument consists of three geographically separate units: Sheep Rock, Painted Hills, and Clarno. The Sheep Rock Unit is located on Highway 19, between the towns of Kimberly and Dayville, Oregon. Prominant, non-fossil bearing rocks date back as far as 95 million years old. Fossils of plants and animals are found in a number of geological layers dating from 33-7 million years ago.
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.
The color really is more of what I would call a sea foam green or a light green blue. However, I have seen others photos of the area where it looked very blue. Not sure how that happens.