The Dalles and Hood River Formations, and the Columbia River Gorge

Abstract

A definite assignment of geologic dates to the main events of the Cenozoic history of the Columbia Gorge and Columbia plateau-vulcanism, sedimentation, folding, erosion-is manifestly possible only if we know the age of at least some of the formations. Because of their stratigraphic position, the ages of The Dalles beds and of the gravels heretofore known as Satsop lying between the Columbia River lavas and the volcanic Cascades formation in the Gorge have critical value for historical purposes. Some doubt has arisen in recent years regarding the extreme youth heretofore assigned to these sedimentary formations and the consequent recency of the physiographic development of the Columbia River Gorge. The writers and Mr. John H. Maxson devoted about ten days in July 1927 to a study of the region extending from somewhat east of The Dalles to west of Hood River. Efforts were concentrated on securing fossil material from the formations lying on the Columbia lavas and on determining the relations of these formations to each other. A very brief preliminary statement of results has been published. The investigation was made under the general direction of Dr. John C. Merriam, President of the Carnegie Institution of Washington, as part of a broad program of Tertiary history' studies in the Northwest.

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