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The Permian and Triassic Seven Devils Group, western Idaho and northeastern Oregon

January 1, 1977

Volcanogenic Permian and Triassic rocks in the Snake River Canyon of western Idaho and northeastern Oregon and in the adjacent Seven Devils Mountains of western Idaho are assigned to the Seven Devils Group. New rock-stratigraphic units are the Windy Ridge Formation of probable Early Permian age, the Hunsaker Creek Formation of Early Permian age, the Wild Sheep Creek Formation of Middle and Late Triassic age, and the Doyle Creek Formation of Late Triassic age. The Pittsburg Formation of former usage is abandoned, the rocks being renamed the Kurry Creek Member and assigned to the newly named Doyle Creek Formation. Overlying strata are the Martin Bridge Limestone of Late Triassic age, the Hurwal Formation of Late Triassic age, the Coon Hollow Formation of Middle(?) and Late Jurassic age, and the Columbia River Basalt Group of Miocene age. Underlying rocks are assemblages of metagabbro, metamorphosed quartz diorite, metabasalt, metadiabase, amphibolite, schist, mylonite, and phyllite that are exposed at The Oxbow of the Snake River near Oxbow, Oreg., along a 7-km segment of the Snake River south of Pittsburg Langing, and near the mouth of the Imnaha River. Gabbro, quartz diorite, and rare granodiorite plutons are concentrated in these assemblages, but some also cut the overlying strata.

The Seven Devils Group is the result of volcanism, tectonism, and sedimentation that occurred within and near volcanic arcs at converging plate boundaries during the Permian and Triassic Periods. Large parts of these old arcs probably were consumed during later subduction, although direct evidence is lacking in the area considered here.

Publication Year 1977
Title The Permian and Triassic Seven Devils Group, western Idaho and northeastern Oregon
DOI 10.3133/b1437
Authors Tracy L. Vallier
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Bulletin
Series Number 1437
Index ID b1437
Record Source USGS Publications Warehouse