Three Fingered Jack

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44.4782° N, 121.8453° WThree 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 consi sts 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. Radiating dikes and plugs that support this summit have been exposed by glaciation. The volcano has long been inactive and has been highly eroded. Show more