Congress set aside about 89 percent of the park in a highly protected wilderness area through passage of the Wilderness Act of 1964. No roads, motorized vehicles (except rescue helicopters and other emergency vehicles), or any development beyond trail maintenance are allowed in this area. The adjacent Ansel Adams Wilderness and John Muir Wilderness were also protected under the act and include regions removed from the park immediately before it was unified with the state grant in 1906.