Sheep Mountain Wilderness is a protected area in southern California within the San Gabriel Mountains National Monument, managed by Angeles National Forest and spanning Los Angeles and San Bernardino counties. Established by the California Wilderness Act of 1984 as part of the National Wilderness Preservation System, it covers 41,883 acres of rugged mountain country, including Iron Mountain at 8,007 feet. The wilderness is known for hiking routes such as the path from Heaton Flat along the East Fork of the San Gabriel River to the Bridge to Nowhere and the trail to Big Horn Mine. That 277-acre property was acquired in 2006, transferred to the U.S. Forest Service, and added to the wilderness.