National monuments are unique among the special and protected land designations on federal public lands, because they are created pursuant to a special, but narrow, grant of authority to the president to regulate federal public lands.

Under the Antiquities Act, the president can essentially sign a proclamation to protect certain areas as national monuments. Once he signs the proclamation, those monuments get immediate protection, and they have to be managed to preserve the special values that are present on the monument. Areas that qualify include sites of historic or cultural significance, or areas of scientific interest—like a region of unusual geologic formations, or areas with ecological or biological significance. There's no size limit on national monuments. They could be as small as a few hundred acres or as large as millions of acres.

Since its enactment, the Antiquities Act has been used more than 150 times to designate and protect national monuments. And some of our western icons—like Grand Canyon National Park, or Bryce National Park, or Zion and Arches National Parks—began life as national monuments. But others have remained national monuments for many decades and have become world-renowned, like the Grand Staircase-Escalante National Monument.

On April 26, 2017, President Trump began a review process and directed the Secretary of Interior to review all monuments designated since 1996 and over 100,000 acres in size, and to make recommendations about their fate.