Three Fingered Jack

Three Fingered Jack, named for its distinctive shape, is a Pleistocene volcano in the Cascade Range of Oregon. It is a deeply glaciated shield volcano and consists mainly of basaltic andesite lava. Compared with other heavily glaciated volcanic peaks such as Mount Washington and Mount Thielsen, which display eroded volcanic necks as their cores, Three Fingered Jack's present summit is a narrow ridge of loose tephra supported by a dike only 10 feet (3.0 m) thick on a generally north–south axis. Radiating dikes and plugs from a series of overlapping cinder and composite cones that support this summit have been exposed by glaciation.

Map of Three Fingered Jack, Oregon 97759, USA

The sole glacier is the unofficially-named Jack glacier, located in a shaded cirque on the northeast side at an unusually low altitude for the Oregon Cascades. The last cone-building eruptions were more explosive in nature than earlier shield-building eruptions, producing mostly unconsolidated strata. Cone-building eruptions ceased before the Pleistocene glacial period, allowing the expanded glacial cover to remove most of the cone.

While sources disagree about who the first ascenders were affiliated with, some sources calling them "the Boys from Bend," others saying they were members of the Mazamas club, one source written by one of these first ascenders clearly states who was in the party and when they climbed. Ervin McNeal, Phil Philbrook, Armin Furrer, Wilbur Watkins, Leo Harryman, and Ronald Sellars were the first to ascend Three Fingered Jack on September 3, 1923.

Three Fingered Jack is located in the Mount Jefferson Wilderness and is not accessible by paved road, but can be approached by the Pacific Crest Trail. It is regarded as extinct and has not been assessed for volcanic hazards.

Several lakes can be found in the vicinity of Three Fingered Jack. These include Marion Lake, Mowich Lake, Duffy Lake, Santiam Lake and Wasco Lake, among others.