ABSTRACT The Columbia River Gorge is the Columbia River’s long-held yet evolving passage through the volcanic arc of the Cascade Range. The globally unique setting of a continental-scale river bisecting an active volcanic arc at the leading edge of a major plate boundary creates a remarkable setting where dynamic volcanic and tectonic processes interact with diverse and energetic fluvial processes. This three-day field trip explores several elements of the gorge and its remarkable geologic history—cast here as a contest between regional tectonic and volcanic processes building and displacing landscapes, and the relentless power of the Columbia River striving to maintain a smooth passage to the sea. This field trip generally follows the GSA guide published in GSA Field Guide 55 (available at https://pubs.geoscienceworld.org/gsa ): O’Connor, J.E., Wells, R.E., Bennett, S.E.K., Cannon, C.M., Staisch, L.M., Anderson, J.L., Pivarunas, A.F., Gordon, G.W., Blakely, R.J., Stelten, M.E., and Evarts, R.C., 2021, Arc versus river—The geology of the Columbia River Gorge, in Booth, A.M., and Grunder, A.L., eds., From Terranes to Terrains: Geologic Field Guides on the Construction and Destruction of the Pacific Northwest: Geological Society of America Field Guide 62, p. 131–186, https://doi.org/10.1130/2021.0062(05) . DEDICATION Dedicated to Russell C. Evarts (7 April 1947–11 July 2017) and his contributions to Pacific Northwest geology. Russ Evarts devoted most of his 30-year career with the U.S. Geological Survey to geologic mapping of Oregon and Washington. His thorough geologic mapping of the near-vertical terrain of the western Columbia River Gorge underpins much of what is reported in this guide and continues to inspire our studies of the geology of the Pacific Northwest.

ABSTRACT The Columbia River Gorge is the Columbia River’s long-held yet evolving passage through the volcanic arc of the Cascade Range. The globally unique setting of a continental-scale river bisecting an active volcanic arc at the leading edge of a major plate boundary creates a remarkable setting where dynamic volcanic and tectonic processes interact with diverse and energetic fluvial processes. This three-day field trip explores several elements of the gorge and its remarkable geologic history—cast here as a contest between regional tectonic and volcanic processes building and displacing landscapes, and the relentless power of the Columbia River striving to maintain a smooth passage to the sea. DEDICATION Dedicated to Russell C. Evarts (7 April 1947–11 July 2017) and his contributions to Pacific Northwest geology. Russ Evarts devoted most of his 30-year career with the U.S. Geological Survey to geologic mapping of Oregon and Washington. His thorough geologic mapping of the near-vertical terrain of the western Columbia River Gorge underpins much of what is reported in this guide and continues to inspire our studies of the geology of the Pacific Northwest.

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