Transcript for Exotic Terrane, segment 06 of 12


The research in the Pacific Ocean continued to solve geologic mysteries in the Pacific Northwest. Geologist Ellen Bishop works in the Greenhorn Mountains of eastern Oregon. This area is known to geologists as the Baker Terrane, which is named after Baker City, Oregon. For years geologists working in the Baker Terrane could not explain how these rocks formed. They are highly altered and mixed up like no other rocks in the region. The mystery was solved when Ellen Bishop was doing research at the Scripps Institution of Oceanography.

My colleagues at Scripps were dredging the Marianas Trench, looking at ocean island systems in the Pacific, and they kept coming home with the same kinds of rocks that I was finding except I didn't have to use a ship and a dredge to find these things. I just had to walk through the Greenhorn Mountains, and I came up with the same mysterious assemblage that they were finding in the South Pacific.

Once again, the present became a crucial link to the past. Ellen Bishop concluded that the Baker Terrane formed at an ancient subduction zone like the Marianas Trench. Her findings complemented the work of geologists in the nearby Wallowa Terrane. When they put their data together, they could see that the two terranes were part of the same ancient island arc. The Wallowa Terrane consisted of the volcanic islands in the arc, and the Baker Terrane was the site of the subduction zone near the islands. The entire geologic feature is called the Blue Mountains Island Arc.

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