At , Mount Jefferson is the second tallest mountain in Oregon. It is a stratovolcano with slopes mantled by five glaciers - Whitewater, Waldo, Milk Creek, Russell, and Jefferson Park. Three Fingered Jack is a heavily eroded and deeply glaciated shield volcano and consists mainly of basaltic andesite lava. At , it is made up of the solidified lava plug flanked by ridges of the old volcano's subsidiary lava dikes and lies at the southern end of the Mount Jefferson Wilderness. Other geographic features of the wilderness include steep talus slopes, rock outcrops, and alpine meadows.