Overview/Background

Sky Lakes Wilderness Geologic History

In terms of geologic time, the Sky Lakes Wilderness is quite young. Its volcanic and glacial history is clearly written in landforms as well as rocks and soil. Studies indicate that the earliest rocks in this part of the High Cascades began forming when a chain of volcanoes erupted between three and five million years ago.

During the "Ice Age", the composite volcanoes of Mt. Mazama and Mt. McLoughlin began their initial build-up less than one million years ago. Just south of Sky Lakes, Brown Mountain produced its extensive lava field as late as 15,000 to 20,000 years ago, and the last eruption of Mt. McLoughlin took place around the same time.On their north and east slopes, Mt. McLoughlin and other peaks bear the scars of glacial ice. Like most other major drainages within Sky Lakes Wilderness, Seven Lakes Basin and the deep canyon of the Rogue River's Middle Fork were carved by the massive ice fields which covered the highest elevations of the Cascades.

With the onset of warmer climate, local glaciers virtually disappeared by 12,000 years ago. Volcanic activity was not yet over, however. Minor lava eruptions and mud-flows occurred at places like Big Bunchgrass Butte and Imagination Peak.

A chain of cinder cones, extending from Goosenest Mountain north into Crater Lake National Park, also formed during the post-glacial period. The most recent - and by far the most catastrophic - geologic event happened about 6,700 years ago, when Mt. Mazama exploded and collapsed, forming the caldera of Crater Lake. Some of the vast amount of rock and ash which was thrown into the air landed in the northern portion of Sky Lakes Wilderness, creating the pumice-covered "Oregon Desert."

Although forests now carpet much of its terrain, Sky Lakes Wilderness retains its character as a land derived from fire and ice.