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Approximately 500,000 years ago, the earth's crust along the Pacific Rim was still constructing itself. However, at that time various peaks of the mighty Cascade Range were considered old and well eroded, except for one, located in the region known today as southern Oregon. The huge volcanic peak called Mt. Mazama, was forming and in the centuries to follow, it eventually caught up to it's other neighbors and experienced glaciation. These glaciers or rivers of ice carved deep valleys extending several miles down the mountains flanks and are still visible today.

In geologically recent times, some 7,700 years ago, the great Mt. Mazama experienced a volcanic eruption many times greater that its Mt. St. Helens cousin in Washington. The character of the eruption was similar, belching pumice and ash that made up two-thirds of the mountains mass and spraying it as far away as Canada, nearly a thousand miles away. Molten lava with intense heat followed, pouring down the slopes, melting the thick mantle of ice from the glaciers, and created unique geologic features. Towering ash and mud spires known today as The Pinnacles stand testament to the surroundings and massive blast.

The mountain itself was finished destroying itself, however erosion actually widened the caldera doubling its diameter. The Pacific Rim was so active that a pair of much smaller volcanic cones later formed in the cooling gargantuan pit.

A long period of further cooling prompted the caldera to eventually fill with the heavy snow fall and summer rains that make up the climate of the Cascade Crest in present day. Over 7,000 years later, an annual snowfall accumulation of 50 feet. The depth of the caldera combined with centuries of heavy precipitation has created the scenic treasure known as Crater Lake.