The Bob Marshall Wilderness Area is a Congressionally designated wilderness area located in western Montana in the United States. It is named after Bob Marshall (1901–1939), an early forester in the federal government, conservationist, and co-founder of The Wilderness Society. In the 1930s while working for the US Forest Service, Marshall was largely responsible for designation of large areas to be preserved as roadless within lands administered by the U.S. Forest Service; he achieved this through promulgation of various regulations. Formally designated in 1964, the Bob Marshall Wilderness extends for 60 miles (95 km) along the Continental Divide and consists of 1,009,356 acres (4,085 km²). As directed by the Wilderness Act of 1964, "The Bob", as it is informally known, is to remain roadless. The only permanent structures here are some old ranger stations and horse bridges. "The Bob" is the fifth-largest wilderness in the lower 48 states (after the Death Valley Wilderness, Frank Church—River of No Return Wilderness, Selway-Bitterroot Wilderness, and Marjory Stoneman Douglas Wilderness). The five ranger districts administering "The Bob" manage 1,856 miles (2,970 km) of trail that are open to foot and stock use only.
