D2 Synorogenic Strata-Dawson Arkose This layer contains several hundred feet of coarse gravel and sandstone layers derived from the uplifted Rocky Mountains. Environments resembled debris fans east of the modern Andes Mountains in South America. These sediments were deposited in the Eocene Epoch (55-50 m.y.a). Typical fossils include petrified wood, leaves, and rare mammal teeth.