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The Western Cascades
Can you imagine a giant meteorite appearing as a dark mass in the sky? Burning its way through the atmosphere in a flash and for only a moment, burning brighter than the sun. Then the crushing sound of an explosion, the rumbling as dark clouds fill the sky. The surface of the ground trembling under foot as the mushroom cloud rises and spreads through the atmosphere. This is probably the image that you would have seen over seventeen million years ago in southeastern Oregon when the Western Cascades were an active chain of volcanoes (Alt 1989).
The Western Cascades providence is distinguished as an older, deeply eroded volcanic range lying west of the more recent snow-covered High Cascade range. The elevation range of these mountains is as low as seventeen hundred feet and as high as five thousand eight hundred feet (US Forest Service). The Western Cascades are made up of somewhat warped and moderately distorted volcanic flows and pyroclastic rocks whose ages range from the late Eocene to the late Miocene (US Forest Service).
According to the Unites States forest service; the Western Cascade Range contains four main units:
1. 0 to 4 m.y. old intracanyon basalt and basaltic andesite flows from the High Cascade Range.
2. 4 to 9 m.y. old basalt and basaltic andesite flows with lesser amounts of andesite and dacite. These rocks which cap the highest Western Cascade ridges were erupted prior to uplift and faulting along the east margin of the ...