Painted Hills

September 15, 2003

Cast_xantho

 

Provided by: Stu Garrett
Summary authors & editors: Stu Garrett

The John Day Fossil Beds National Monument is one of 5 national monuments in Oregon. This spectacular area is covered with multicolored hills, rolling terrain, and shows much evidence of its violent past. The John Day Formation was deposited from 39 to 18 million years ago. It records the early volcanism of the Western Cascade Range and marks a late-Eocene westward jump of the offshore Cascades subduction zone. Eruptions spewed out light-colored rhyolite in explosive eruptions that accumulated as air-fall material in lake and stream environments.

The red hills of the lower John Day Formation are composed of reworked Clarno saprolite and take their color from iron oxides. These soils are selenium-deficient and titanium-enriched and only certain plants have been able to adapt to them. The small green Indian Paintbrush in the foreground of the photo is one of these endemic plants (Castilleja xanthotricha), the John Day Paintbrush. It's found only on the unusual soils of the John Day formation in Central Oregon.

The John Day Formation became famous early in Oregon’s history. Thomas Condon was a minister who visited the area in 1865. He became the first geology professor at the University of Oregon in 1876 and first studied the local fossils. Army officers fighting Indians in the area made him aware of the fossils. A major part of the North American animal and plant fossil record of the last 40 million years derives from Oregon’s John Day Formation.

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