Three Sisters (Oregon)

The Three Sisters are at the boundary of Lane and Deschutes counties and the Willamette and Deschutes national forests in the U.S. state of Oregon, about south of the nearest town of Sisters. The three peaks are the third-, fourth-, and fifth-highest in Oregon, and contain 16 named glaciers. Their ice volume totals . The Sisters were named Faith, Hope and Charity by early settlers, but are now known as North Sister, Middle Sister and South Sister, respectively. Wilderness The Three Sisters Wilderness covers an area of , making it the second-largest wilderness area in Oregon. Designated by the United States Congress in 1964, it borders the Mount Washington Wilderness to the north and shares its southern edge with the Waldo Lake Wilderness. The area includes of trails and many forests, lakes, waterfalls, and streams, including the source of Whychus Creek. 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 to in elevation, the Alpine Crest Region features the wilderness area's most-frequented glaciers, lakes, and meadows. Physical geography Weather varies greatly in the area due to the rain shadow caused by the Cascade Range. Air from the Pacific Ocean rises over the western slopes, which causes it to cool and dump its moisture as rain (or snow in the winter). Precipitation increases with elevation. Once the moisture is wrung from the air, the air descends on the eastern side of the crest, which causes it to become warmer and drier. On the western slopes, precipitation ranges from annually, while precipitation over the eastern slopes varies from in the east. Temperature extremes reach in summers and during the winters. The Three Sisters have about 130 snowfields and glaciers ranging in altitude from with a cumulative surface area of about . The Linn and Villard Glaciers are north of the North Sister summit, while the Thayer Glacier is on its eastern slope. The Collier Glacier is nestled between North Sister and Middle Sister and flows to the northwest. The Renfrew and Hayden Glaciers are on the northwestern and northeastern slopes of Middle Sister, respectively, while the Diller Glacier is on its southeastern slope. The Irving, Carver and Skinner Glaciers lie between Middle Sister and South Sister. Finally, around the summit of South Sister, in a clockwise direction, are the Prouty, Lewis, Clark, Lost Creek, and Eugene Glaciers. In September 2012, a lightning strike caused a fire that burned in the Pole Creek area within the Three Sisters Wilderness, leaving the area closed until May 2013. In August 2017, officials closed in the western half of the Three Sisters Wilderness, including of the Pacific Crest Trail, to the public because of 11 lightning-caused fires, including the Milli Fire. As a result of the increasing incidence of fires, public officials have factored the role of wildfire into planning, ==Geology==

The Three Sisters join several other volcanoes in the eastern segment of the Cascade Range known as the High Cascades, which trends north–south. The High Cascades are the most recent volcanic arc in the Pacific Northwest, which forms the Cascade Volcanoes. These volcanoes, including the Three Sisters, were fed by magma chambers resulting from the subduction of the Juan de Fuca tectonic plate under the western edge of the North American tectonic plate. Each of the three volcanoes formed at different times from several variable magmatic sources. The amount of rhyolite present in the lavas of the younger two mountains is unusual relative to nearby peaks. The oldest lava flows on North Sister have been dated to roughly 311,000 years ago, though the oldest reliably dated deposits are approximately 119,000 years old. Estimates place the volcano's last eruption at 46,000 years ago, in the Late Pleistocene. North Sister possesses more dikes than any similar Cascade peak, caused by lava intruding into pre-existing rocks. Many of these dikes were pushed aside by the intrusion of a -wide volcanic plug. The dikes and plug were exposed by centuries of erosion. The smallest and least studied of the three, Middle Sister began eruptive activity 48,000 years ago, and it was primarily built by eruptions occurring between 25,000 and 18,000 years ago. One of the earliest major eruptive events (about 38,000 years ago) produced the rhyolite of Obsidian Cliffs on the mountain's northwestern flank. Thick and rich in dacite, the flows extended from the northern and southern sides. They stand in contrast to older, andesitic lava remains that reach as far as from its base. With an elevation of , It is a predominantly rhyolitic stratovolcano overlying an older shield structure. Its modern structure is no more than 50,000 years old, and it last erupted about 2,000 years ago. A 2002 study inferred that the inflation was due to intruding magma, likely of basaltic to rhyolitic composition, into an existing magma reservoir. A 2011 study described the cumulative magma intrusion as in volume. Beginning in 2001, the Cascades Volcano Observatory conducted field surveys and installed two new monitoring stations near the Three Sisters, including a GPS station and seismometer at The Husband, a peak west of the Three Sisters. In 2004, this seismometer detected an earthquake swarm in the area of uplift. The hundreds of small earthquakes subsided after several days. According to a 2011 study, this swarm may have initiated a significant decrease in the peak uplift rate. GPS and satellite observations showed that the rate of uplift west of South Sister gradually decreased from 2001 to 2020. A small increase in the uplift rate began in the same area between 2020 and 2021, and small earthquake swarms were recorded in 2021 and 2022. == Ecology ==

The ecology of the Three Sisters reflect their location in central Oregon's Cascade Range. The westside slopes from lie in the Western Cascade Montane Highlands ecoregion, where precipitation is abundant. Forests here consist predominantly of Douglas-fir and western hemlock, with minor components of mountain hemlock, noble fir, subalpine fir, grand fir, Pacific silver fir, red alder, and Pacific yew. Vine maples, rhododendron, Oregon grape, huckleberry, and thimbleberry grow beneath the trees. Douglas-fir is dominant below , while western hemlock dominates above. Timberline at the Three Sisters occurs at , where the forest canopy opens and the subalpine zone begins. These forests lie in the Cascade Crest montane forest ecoregion. Mountain hemlock trees dominate the forest in this area, while meadows sustain sedges, dwarf willows, tufted hairgrass, lupine, red paintbrush, and Newberry knotweed. Tree line occurs at . The vegetation in this harsh alpine zone consists of herbaceous and shrubby subalpine meadows. This zone has a large winter snowpack, with low temperatures for much of the year. There are patches of mountain hemlock, subalpine fir, and whitebark pine near the treeline, as well as wet meadows supporting Brewer's sedge, Holm's sedge, black alpine sedge, tufted hairgrass, and alpine aster. Near the peaks of the Three Sisters, there are extensive areas of bare rock. The lower eastern slopes of the Three Sisters below lie in the Ponderosa Pine/Bitterbrush Woodland ecoregion. This ecoregion has less precipitation than the western slopes and has soil derived from Mazama Ash (ash erupted from Mount Mazama). Stream flow changes little throughout the year due to the region's volcanic hydrogeology. These slopes support nearly pure stands of ponderosa pine. Understory vegetation includes greenleaf manzanita and snowberry at higher elevations and antelope bitterbrush at lower elevations. Mountain alder, stream dogwood, willows, and sedges grow along streams. Local fauna includes birds such as blue and ruffed grouse, small mammals like pikas, chipmunks, and golden-mantled ground squirrels, and larger species like the Columbian black-tailed deer, mule deer, Roosevelt elk, and American black bear. Bobcats, cougars, coyotes, wolverines, martens, badgers, weasels, bald eagles, and several hawk species are many of the predators throughout the Three Sisters area. == Human history ==

The Three Sisters area was occupied by Amerindians since the end of the last glaciation, mainly the Northern Paiute to the east and Molala to the west. They harvested berries, made baskets, hunted, and made obsidian arrowheads and spears. Traces of rock art can be seen at Devils Hill, south of South Sister. The first Westerner to discover the Three Sisters was the explorer Peter Skene Ogden of the Hudson's Bay Company in 1825. He describes "a number of high mountains" south of Mount Hood. Ten months later in 1826, the botanist David Douglas reported snow-covered peaks visible from the Willamette Valley. As the Willamette Valley was gradually colonized in the 1840s, Euro-Americans approached the summits from the west and probably named them individually at that time. Explorers, such as Nathaniel Jarvis Wyeth in 1839 and John Frémont in 1843, used the Three Sisters as a landmark from the east. The area was further explored by John Strong Newberry in 1855 as part of the Pacific Railroad Surveys. In 1862, to connect the Willamette Valley to the ranches of Central Oregon and the gold mines of eastern Oregon and Idaho, Felix and Marion Scott traced a route over Scott Pass. This route was known as the Scott Trail, but was superseded in the early 20th century by the McKenzie Pass Road further north. In February 1866, the Seattle Weekly Gazette reported that one of the Three Sisters emitted some fire and smoke. In the late 19th century, there was extensive wool production in eastern Oregon. Shepherds led their herds of 1,500 to 2,500 sheep to the Three Sisters. They arrived in eastern foothills near Whychus Creek by May or June, and then climbed to higher pastures in August and September. By the 1890s, the area was getting overgrazed. Despite regulatory measures, sheep grazing peaked in 1910 before being banned in the 1930s at North and Middle Sister, and in 1940 at South Sister. In 1892, President Grover Cleveland decided to create the Cascades Forest Reserve, based on the authority of the Forest Reserve Act of 1891. Cascades Reserve was a strip of land from wide around the main crest of the Cascade Range, stretching from the Columbia River almost to the border with California. In 1905, administration of the Reserve was moved from the United States General Land Office to the United States Forest Service. The Reserve was renamed the Cascade National Forest in 1907. In 1908, the forest was split: the eastern half became the Deschutes National Forest, while the western half merged in 1934 to form the Willamette National Forest. Most of the Three Sisters glaciers were described for the first time by Ira A. Williams in 1916. Collier Glacier, between North and Middle Sister, was first studied and mapped by Edwin Hodge. Ruth Hopsen Keen took a forty-year photographic record of Collier Glacier, documenting part of the retreat of the glacier from 1910 to 1994. In the 1930s, the Three Sisters were part of a proposed National Monument. To maintain its authority over the region, the Forest Service decided to create a primitive area in 1937. The following year, at the instigation of Forest Service employee Bob Marshall, it was expanded by in the French Pete Creek basin. In 1957, the Forest Service decided to reclassify the area as a wilderness area and removed the old-growth forest of the French Pete Creek basin, despite protests of local environmental activists. The area became part of the National Wilderness Preservation System when the Wilderness Act of 1964 was passed, but the area still excluded the French Pete Creek basin. Responding to environmental mobilization throughout the state of Oregon, Congress passed the Endangered American Wilderness Act of 1978, which led to the reinstatement of French Pete Creek and its surroundings in the Three Sisters Wilderness Area. The Oregon Wilderness Act of 1984 further expanded the wilderness with the addition of around Erma Bell Lakes. == Recreation ==

in the Three Sisters Wilderness|alt=Two hikers with backpacks walk along a trail in the Three Sisters Wilderness, surrounded by trees with the Three Sisters visible in the background. The Three Sisters are a popular climbing destination for hikers and mountaineers. Due to extensive erosion and rockfall, North Sister is the most dangerous climb of the three peaks, and is often informally called the "Beast of the Cascades". One of its peaks, Little Brother, can be safely scrambled. The first recorded ascent of North Sister was made in 1857 by six people, including Oregon politicians George Lemuel Woods and James McBride, according to a story published in Overland Monthly in 1870. Today, the common trail covers round-trip, gaining in elevation. Middle Sister can also be scrambled, for a round trip of and an elevation gain of . South Sister is the easiest of the three to climb, and has a trail all the way to the summit. The standard route up the south ridge runs for round trip, rising from at the trailhead to at its summit. It is a popular climb during August and September, with up to 400 people each day. ==See also==