Geological Tour of Poly Canyon Eastern View of Bedrock

Looking east toward the axis of a structural syncline that parallels Cuesta Ridge. The brown grasses are underlain by the Franciscan Formation melanges, dominated by highly sheared shales. The dark vegetation is comprised of much younger marine shales and volcanic deposits of Miocene age. These were deposited on the eroded Franciscan Formation after it was uplifted into mountains and then eroded again to below sea level. This is a good example of how bedrock has affected the vegetation, and you can clearly see the unconformity between the Franciscan Formation and the younger rocks.