Geology
Volcanic activity in the region has been traced to 40 million years ago, in the Eocene era, forming much of the region's landscape. In the Pleistocene era (the last ice age, two million to 700,000 years ago), the Columbia River broke through Cascade Range, forming the Columbia River Gorge.
The Columbia River and its drainage basin experienced some of the world’s greatest known floods toward the end of the last ice age. The periodic rupturing of ice dams at Glacial Lake Missoula resulted in discharge rates ten times the combined flow of all the rivers of the world, as many as forty times over a thousand-year period.
Water levels during the Missoula Floods have been estimated at 1,250 feet (381 m) at the Wallula Gap (in present-day Washington), 830 feet (253 m) at Bonneville Dam, and 400 feet (122 m) over current day Portland, Oregon. The floods' periodic inundation of the lower Columbia River Plateau deposited rich lake sediments, establishing the fertility that supports extensive agriculture in the modern era. They also formed many unusual geological features, such as the channeled scablands of eastern Washington.
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.
The Klamath Native Americans of the area thought that the mountain was inhabited by Llao, their god of the underworld. After the mountain destroyed itself the Klamaths recounted the events as a great battle between Llao and his rival Skell, their sky god.
The 1700 Cascadia earthquake resulted from a rupture in the Juan de Fuca Plate along the coast of the Pacific Northwest. The earthquake caused a tsunami that was detected in Japan; it may also be linked to the Bonneville Slide, in which a large part of Washington's Table Mountain collapsed into the Columbia River Gorge, damming the river and forming the Bridge of the Gods, a land bridge remembered in the oral history of local Native Americans.
In 1980, Mount St. Helens in neighboring Washington erupted violently, temporarily reducing the Columbia River's depth to as little as 13 feet, and disrupting Portland's economy. The eruption deposited ash as far into Oregon as Bend.
Read more about this topic: History Of Oregon