The Three Sisters Wilderness covers an area of , making it the second-largest wilderness area in Oregon, after the Eagle Cap Wilderness area. 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 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.