Bingo: National Monument
A national monument is a section of public land set aside for its natural, historical, or cultural value. National monuments range from structures to oceans to large tracts of land.
The Antiquities Act was established in 1906 by Theodore Roosevelt and has been used more than a hundred times since its passage. It gives the President of the USA the authority to create national monuments from existing public lands to protect significant natural, cultural, or scientific features.
FYI: The Grand Canyon was designated a national monument before it became a national park.