PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2009-11-15 NOTE = "Geologic setting description" END_OBJECT = TEXT END Volcanoes dominate the landscape of Central Oregon, and volcanism has characterized and shaped the region for the past 45 million years. The most recent eruption occurred at Newberry Crater 1300 years ago, forming Big Obsidian Flow. Fossil evidence indicates that warm seas once covered Oregon until about 70 million years ago when volcanoes and uplift ended this era. 17 million years ago rainfall decreased and volcanic activity sent floods of lava, now known as the Columbia River basalts, east of the Cascade Mountains. For 5 million years, heavy lava flows continued and buried everything in their path except for the highest mountains and hilltops. The Cascades have grown in numerous volcanic events occurring from about 40 million years ago to the present. In the lowlands, hundreds of feet of sand, gravel, ash, pumice, and lava have accumulated from erosion and eruptions in the Green Ridge area, north of the town of Sisters. This deposited material comprises the Deschutes Formation of Cove Palisade State Park. Formation history & description: The Deschutes River, driven by a 600 m fall, flows northward, meandering across the floor of the High Cascades and Newberry?s lava plains, carving out the canyons of Cove Palisades State Park and offering a view into geologic history, presented by the dramatic Deschutes Formation. About 8 million years ago, volcanic activity began to influence the Deschutes River. The increasing volcanism deposited a great amount of volcanic debris and clogged the drainage of the river. The multicolored sands and volcanic flows that comprise the layered canyon walls now known as the Deschutes Formation were deposited between 8 and 4 million years ago. These deposits include basalt flows, ash-flow tuffs known as ignimbrites, and flood-generated layers of sand and gravel. The Deschutes Formation?s maximum thickness is 700 meters. Generally, volcanic rock strata, both flows and ignimbrites, are thicker and more abundant as one moves westward. Ignimbrites are most common and well preserved in the basin?s center. Sediment deposits become thicker and finer grained as one moves eastward through the Formation. References: Bishop, Ellen Morris and Gary A. Smith. "A field guide to the geology of Cove Palisades State Park and the Deschutes Basin in central Oregon." Oregon Geology Jan 1990 3-12. 23 Aug 2007. Chitwood, Larry. "A Brief Summary of the Geology of Central Oregon." Deschutes & Ochoco National Forests. 26 Nov 2003. USDA Forest Service . 23 Aug 2007 . Description submitted by: M. Bjella