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The history of Oregon, a U.S. state, may be considered in five eras: geologic history, inhabitation by native peoples, early exploration by Europeans (primarily fur traders), settlement by pioneers, and modern development. The term "Oregon" may refer to: *Oregon Country, a large region explored by Americans and Britons (and generally known to Canadians as the Columbia District); *Oregon Territory, established by the United States two years after its sovereignty over the region was established by the Oregon Treaty; and *Oregon, a U.S. state since 1859 ==Geology== (詳細は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.〔(【引用サイトリンク】url=http://vulcan.wr.usgs.gov/Volcanoes/Washington/ColumbiaRiver/geo_history_gorge.html )〕 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.〔(【引用サイトリンク】 publisher =U.S. Geological Survey )〕 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.〔(Great Cascadia Earthquake Penrose Conference )〕 The earthquake caused a tsunami that was detected in Japan;〔(Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions )〕 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. Celilo Falls, a series of rapids on the Columbia River just upstream of present-day The Dalles, Oregon, was a fishing site for natives for several millennia. Native people traveled to Celilo Village from all over the Pacific Northwest and beyond to trade. The rapids were submerged in 1957 with the construction of The Dalles Dam. In 1980, Mount St. Helens in nearby 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.〔Harris, Stephen L. (1988). ''Fire Mountains of the West: The Cascade and Mono Lake Volcanoes''. Missoula: Mountain Press Publishing Company, Missoula. ISBN 0-87842-220-X〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of Oregon」の詳細全文を読む スポンサード リンク
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