Rock Layers, Dawson Arkose



		D2 Synorogenic Strata: 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. Dawson Arkose: A sedimentary unit rich in quartz and feldspar typified by outcrops on Dawson Butte and road cuts on Interstate 25 near Larkspur. The Dawson Arkose interfingers with the Denver Formation, making regional mapping difficult. Our terminology ascribes the lower portion of the Dawson Arkose to D1 Synorogenic Strata and the upper portion of it to D2 Synorogenic Strata.

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	A) The Dawson Arkose was deposited by braided streams flowing off of the young Rocky Mountains, which resembled environments east of the modern Andes Mountains in South America. B) Fossil Leaf, Macginitiea. C) Outcrop of D2 Strata near Castle Rock, Colorado. D) Fossil log near Parker, Colorado.