There are 128 protected areas in the United States known as national monuments. The President of the United States can establish a national monument by presidential proclamation, while the United States Congress can do so by legislation. The president's authority arises from the Antiquities Act of 1906, which authorizes the president to proclaim "historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest" as national monuments. Concerns about protecting mostly prehistoric Indian ruins and artifacts—collectively termed antiquities—on western federal lands prompted the legislation. Its purpose was to allow the president to quickly preserve public land without waiting for legislation to pass through an unconcerned Congress. The ultimate goal was to protect all historic and prehistoric sites on U.S. federal lands. President Theodore Roosevelt established the first national monument, Devils Tower in Wyoming, on September 24, 1906. He established eighteen national monuments, although only nine still retain that designation. Seventeen presidents have created national monuments under the Antiquities Act since the program began; only Richard Nixon, Ronald Reagan, and George H. W. Bush did not. Bill Clinton created nineteen and expanded three others. Jimmy Carter protected vast parts of Alaska, proclaiming fifteen national monuments, some of which later were promoted to national parks. President Barack Obama created or expanded thirty-four national monuments by proclamation, the most of any president, with over half a billion acres of public land and water protected. National monuments are located in 31 states as well as in the District of Columbia, the Virgin Islands, American Samoa, the Minor Outlying Islands, and the Northern Mariana Islands. Arizona and California have the most national monuments, each with 18, followed by New Mexico with 13. At least seventy-four national monuments protect places of natural significance, including nineteen primarily for their geological features, eight marine sites, and eight volcanic sites. Sixty-two national monuments protect historic sites, including twenty-seven associated with Native Americans, nine relating to African American history, and ten forts. Four have been designated World Heritage Sites. Two national monuments, Medgar and Myrlie Evers Home and Mill Springs Battlefield, have been authorized but not yet established as units, pending property acquisition by the National Park Service; they are listed below but are not yet included in the total counts. Many :Category:Former National Monuments of the United States|former national monuments have been redesignated as national parks or another status by Congress, while others have been transferred to state control or disbanded.
Eight federal agencies in five departments manage the 128 current U.S. national monuments. Of these, 114 monuments are managed by a single agency, while 14 are co-managed by two agencies. One of the NPS's national monuments, Grand Canyon-Parashant, is not an official unit because it overlaps with Lake Mead National Recreation Area.
