The Sheep Rock Unit contains an amalgam of colorful strata and complex geology. From Cretaceous conglomerates to the flood basalts, the geologic features in this portion of the monument are a spectacle to behold.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.
Fossil Layers of the Sheep Rock Unit
Turtle Cove Assemblage (30-25 Ma)
Turtle Cove is the thickest and most productive fossil-bearing layer within the John Day Fossil Beds, yet few leaf fossils were preserved.
Upper John Day Assemblage (24-20 Ma)
The ecosystem became an open habitat with the appearance of burrowing and running animals.
Other Places to Visit in the Monument
The Clarno Unit has the oldest exposed layers of the park, and the only unit with fossils along the trail. Remember, no collecting fossils.
Painted Hills Unit
The colorful stripes and gentle ripples of the Painted Hills makes it one of the most popular destinations in the park.
Thomas Condon Visitor Center
The Thomas Condon Visitor Center displays fossils from the entirety of the John Day Fossil Beds.
Last updated: January 5, 2023