ARCHIVED - It’s Here That Oregon Began - Oregon Historical Markers on Waymarking.com

The ranger station was destroyed by fire on the evening of July 11, 2010.

This history sign was on the deck at the Eagle Cap Ranger District Office and Visitor Center at Enterprise, Oregon. There are two other interpretive signs with non history subjects. Marker Name: It’s Here That Oregon Began
Marker Text: Imagine yourself in the tropics! The rocks that floor Hells Canyon and cap the Wallowas were formed by an arc of volcanic islands in the ocean west of North America about 300 to 200 million years ago. Coral reefs and ichthyosaurs (marine reptiles related to the dinosaurs) flourished in warm seas nearby. Volcanic activity subsided about 180 million years ago. Gradually a blanket of sand and mud covered the extinct volcanoesa. Moving plates of the earth’s crust drove the extinct island arc terrane to its collision with North America.
COLLISION AND ACCRETION
140 to 110 million years ago, the extinct volcanic islands slowly collided with the North American coast in the area of present-day Idaho. As subduction stopped, folding and faulting welded this terrane to the continent. Heat and pressure from the collision melted the Earth’s lower crust, creating the magmas that gave birth to the granitic rocks of Idaho and Northeast Oregon, including the Wallowas. The tropical islands had now become part of North America’s newest mountain range.
EROSION
Water and wind carved away at the new mountains of North America for the next 85 million years. Then approximately 50 million years ago, subduction began again, producing volcanoes in the Clarno and John Day areas and in the Cascade Range. As Oregon continued to build westward, the geologic wreckage of the old island arc terranes was left behind to be worn down to a nearly flat landscape.
COLUMBIA RIVER BASALT
17 to 15 million years ago, basalt flows erupted from dikes and linear vents in Eastern Oregon and Washington. These lavas flooded over 60,000 square miles of this flat landscape. Within weeks, some of these flows traveled from Idaho to the Pacific Ocean! Small eruptions continued until 6 million years ago. When the eruptions ceased, the old island arc rocks were buried beneath basalt almost 2 miles thick!
FAULTING AND UPLIFT
As the basalt eruptions dwindled 6 million years ago, plate tectonic forces stretched the crust of Oregon and Nevada westward. Faulting uplifted the Wallowas and down-dropped surrounding valleys including the Grande Ronde. During the last 2 million years, a steepened and invigorated Snake River gouged through the basalt flows and the old volcanic rocks below, forming Hells Canyon.
GLACIATION - PAST, PRESENT AND FUTURE
The Wallowa Mountains’ sharp peaks and U-shaped valleys testify that glaciers advanced and retreated several times during the last million years. These glaciers built the moraines that surround Wallowa lake, retreatin only 10,000 years ago. Today, uplift continues. Streams carry fragments of the old volcanic rocks back to the sea once again. The conflict between forces deep within the Earth and on the Earth’s surface is never-ending!

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