San Gabriel Mountains National Monument protects a large swath of the central and northern San Gabriel Mountains in California, within parts of the Angeles and San Bernardino national forests. Established in 2014 under the Antiquities Act, it preserved 346,177 acres after more than a century of conservation efforts that began with the San Gabriel Timberland Reserve in 1891 and later campaigns for monument status. The protected area includes major wilderness areas, prominent peaks, and the Silver Moccasin Trail, while leaving some southern sections outside its boundaries. Its creation reflected the range’s importance for open space, drinking water, and public access for millions near Los Angeles, and it was expanded in 2024.