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The Three Sisters and nearby Broken Top account for about a third of the Three Sisters Wilderness, and this area is known as the Alpine Crest Region. Rising from about 5,200 ft (1,600 m) to 10,358 ft (3,157 m) in elevation, the Alpine Crest Region features the wilderness area's most-frequented glaciers, lakes, and meadows.
It comprises 286,708 acres (1,160.27 km 2), making it the second largest wilderness area in Oregon, after the Eagle Cap Wilderness. It was established by the United States Congress in 1964 and is named for the Three Sisters volcanoes. The wilderness boundary encloses the Three Sisters as well as Broken Top, which is southeast of South Sister. [2]
Broken Top is a glacially eroded complex stratovolcano.It lies in the Cascade Volcanic Arc, part of the extensive Cascade Range in the U.S. state of Oregon.Located southeast of the Three Sisters peaks, the volcano, residing within the Three Sisters Wilderness, [4] is 20 miles (32 km) west of Bend, Oregon in Deschutes County.
The three most recent were Lassen Peak from 1914 to 1921, a major eruption of Mount St. Helens in 1980, and a minor eruption of Mount St. Helens from 2004 to 2008. [25] In contrast, volcanoes in southern British Columbia, central and southern Oregon are currently dormant.
Belknap was the last volcano to erupt in the Three Sisters area. [21] Basaltic andesite dominates the eruptive material in the local mafic volcanoes, which range from early Pleistocene to Holocene age. [22] Belknap is one of the larger mafic volcanoes in the Sisters Reach, more than 30 of which run continuously along the segment. [22]
Mount Bachelor from Little Lava Lake (southwest of the mountain). Mount Bachelor lies in the Cascade Range, within Deschutes County, in the U.S. state of Oregon. [2] It is located south of the Three Sisters complex volcano, [5] and reaches an elevation of 9,068 feet (2,764 m).
Three Fingered Jack (northcentral Oregon) — Highly eroded Pleistocene volcano. Mount Washington (between Santiam and McKenzie passes) — a highly eroded shield volcano. [3] Three Sisters (near the city of Bend, Oregon) — South Sister is the highest and youngest, with a well-defined crater. Middle Sister is more pyramidal and eroded.
All three volcanoes are part of the Oregon High Cascades, a range that sections off the stratovolcanoes of Oregon that are younger than 3.5 million years. The High Cascades include Mount Jefferson, the Three Sisters, Broken Top, and other stratovolcanoes and remnants. [13] Rock in the area ages from the Upper Pliocene and Quaternary. Basalt and ...