Crater Lake is formed from the caldera of Mount Mazama. Part of the Cascades volcanic chain, Mount Mazama sits between the Three Sisters volcanoes to the north and Mount Shasta to the south. The catastrophic eruption of Mount Mazama that occurred approximately 7,700 years ago destroyed the volcano while simultaneously forming the basin for Crater Lake. Eruptive activity continued in the region for perhaps a few hundred years after the major eruption. Evidence of this activity lingers in volcanic rocks, lava flows, and domes beneath the lake surface; the small cone of Wizard Island is the only visible portion of these younger rocks.
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