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| Columbia River Flood Basalts -- This one-kilometer-thick section of the Columbia River Flood basalts is well-exposed in the Snake River Canyon near the Washington-Oregon-Idaho tri-state area. The prominent bench about halfway up the section marks the boundary between the Imnaha basalts and the overlying Grande Ronde basalts. The voluminous CRB sequence erupted from fissures in northeastern Oregon and southeastern Washington from 17 to 6 million years ago. However, about 90% of the total basalt volume erupted between 17 and 14 million years ago. Photo by Vic Camp. |