Mount Mazama , once the tallest mountain in the region at 11,000 feet , had a massive volcanic eruption approximately 5677 B.C . The eruption , estimated to have been 42 times more powerful than the 1980 eruption of Mount St. Helens , reduced Mazama 's approximate 11,000 foot ( c. 3,350 m ) height by around half a mile ( about 1 km ) when much of the volcano fell into the volcano 's partially emptied neck and magma chamber . Mazama 's collapsed caldera , in today 's southern Oregon , contains Crater Lake , and the entire mountain is located in Crater Lake National Park
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
History of Oregon