Three Fingered Jack is a summit of a shield volcano of the Cascade Range in the U.S. state of Oregon. Formed during the Pleistocene epoch, the mountain consists mainly of basaltic andesite lava and was heavily glaciated in the past. While other Oregon volcanoes that were heavily glaciated—such as Mount Washington and Mount Thielsen—display eroded volcanic necks, Three Fingered Jack's present summit is a comparatively narrow ridge of loose tephra supported by a dike only 10 feet (3.0 m) thick on a generally north–south axis. Glaciation exposed radiating dikes and plugs that support this summit. The volcano has long been inactive and is highly eroded. Three Fingered Jack has diverse flora, fauna, and fungi. The Molala people, one of the indigenous groups in the northwestern United States, historically inhabited the area around the volcano. Not much is known about Molala culture, other than that the group fished for salmon and collected berries, fruits, obsidian, and dried herbs. David Douglas was the first person of non-indigenous descent to reach the area in 1825, followed by Peter Skene Ogden the following year. The first group to ascend the volcano reached its summit in September 1923. Three Fingered Jack can still be climbed, but climbers can require rescue after becoming disoriented in low visibility conditions.
Geography Three Fingered Jack lies in the U.S. state of Oregon, in Linn and Jefferson counties. It has a volume of 2.4 cubic miles (10 km3) and a summit elevation of 7,844 feet (2,391 m), with a proximal topographic relief of 1,300 feet (400 m) and a draping relief of 4,600 feet (1,400 m). Its jagged edifice rises between Mount Jefferson and the Three Sisters volcanic complex. Three Fingered Jack lies within the Mount Jefferson Wilderness and is only accessible on foot by trails such as the Pacific Crest Trail. Located about 20 miles (32 km) northwest of the city of Sisters, it is a prominent landmark in the area.
Physical geography
Lateral and terminal moraines formed on Three Fingered Jack during the last major advance of glacial ice in the area during the Wisconsin glaciation, along with glacial striations, altered vegetation patterns, and lithologies that suggest glacial transport of material. Jack Glacier (unofficially-named) is the sole glacier remaining on the volcano, located in a shaded cirque on the northeast side. The glacier resides at an unusually low altitude for the central Oregon Cascades it is protected by tall ridges to the south and west. Jack Glacier has an area of 2.5 acres (1.0 ha), though historically it has reached estimated areas of up to 32 acres (13 ha). It is likely stagnant. During the Little Ice Age, which spanned roughly 1350 to 1850, the glacier produced moraines with heights close to 200 feet (61 m), which are dotted with 1⁄2 to 1 foot (0.15 to 0.30 m) of ash from the Sand Mountain cinder cone chain and 1 foot (0.30 m) of ash from the Blue Lake Crater cinder cone. The moraine for Jack Glacier dammed a lake with a volume of 940,000 cubic feet (26,500 m3), a surface area of 65,900 square feet (6,120 m2), and a maximum depth of 26 feet (8 m). This lake was documented in 1937, although it did not appear on United States Geological Survey topographic maps made during the 1920s. The lake sits precariously; moraines on the volcano are steep, unstable, and populated with boulders. Before September 1960, there was a partial breach of this moraine-dammed lake that covered an area of 12,000 square metres (3.0 acres) near the moraine's base. Since 1960, there have been at least three incidents in which moraine-dammed lakes on the volcano have caused floods down the slopes, including a significant flood and debris flow in 2012. Local soil is thin, and it has been buried by a layer of weathered Holocene tephra from Three Fingered Jack, which has a maximum thickness of 3.3 feet (1 m).
Ecology
Douglas fir, Alpine fir, blue spruce, mountain hemlock, and bear grass can be found along the volcano and its hiking trails. Cascade parsley fern grows on Three Fingered Jack between elevations of 6,500 to 7,000 feet (2,000 to 2,100 m). There are also mountain goats in the surrounding wilderness area. Carnivorous animals in the surrounding area include American black bears, coyotes, cougars, red foxes, raccoons, American martens, stoats (also known as ermines), long-tailed weasels, American minks, North American river otters, and bobcats. Deer species include Roosevelt elk, black-tailed deer, and mule deer; insectivores include vagrant shrews, American water shrews, and coast moles. Bats at Jefferson include little brown bats and silver-haired bats, and American pikas and snowshoe hares are also present. Rodents such as yellow-bellied marmots, mountain beavers, yellow-pine chipmunks, Townsend's chipmunks, golden-mantled ground squirrels, western gray squirrels, Douglas squirrels, mountain pocket gophers, North American beavers, deer mice, bushy-tailed woodrats, water voles, Pacific jumping mice, and North American porcupines are present. Birds nearby include mallards, American goshawks, sharp-shinned hawks, red-tailed hawks, dusky grouse, grey partridges, killdeer, spotted sandpipers, California gulls, band-tailed pigeons, great horned owls, mountain pygmy owls, common nighthawks, rufous hummingbirds, Northern flickers, pileated woodpeckers, yellow-bellied sapsuckers, hairy woodpeckers, and white-headed woodpeckers. Other bird species found in the area consist of American three-toed woodpeckers, willow flycatchers, olive-sided flycatchers, tree swallows, Canada jays, Steller's jays, common ravens, Clark's nutcrackers, black-capped chickadees, mountain chickadees, chestnut-backed chickadees, red-breasted nuthatches, pygmy nuthatches, brown creepers, American dippers, wrens, American robins, varied thrushes, hermit thrushes, Townsend's solitaires, golden-crowned kinglets, ruby-crowned kinglets, American pipits, blue-headed vireos, western tanagers, Cassin's finches, gray-crowned rosy finches, pine siskins, red crossbills, green-tailed towhees, dark-eyed juncos, white-crowned sparrows, golden-crowned sparrows, fox sparrows, and Lincoln's sparrows. Long-toed salamanders, California giant salamanders, rough-skinned newts, tailed frogs, western toads, Pacific tree frogs, northern red-legged frogs, Oregon spotted frogs, pygmy short-horned lizards, common garter snakes, and northwestern garter snakes make up some of the amphibious and reptilian animals in the vicinity.
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