THE ANTIQUITIES ACT OF 1906
President Obama's Proclamation 9233 of February 19, 2016 established the Pullman National Monument in accordance with the Antiquities Act of 1906 ("the Act"). This legislation, along with other National Park Service and Historic Preservation law, was compiled into Title 54 of the United States Code in 2014. You can read the current text of the Act in 54 U.S.C. § 320301.
The Act has two implied powers: 1) the declaration power and 2) the reservation power.
The declaration power allows a president to "declare" a national monument by public proclamation for the purpose of protecting "historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest."
The reservation power allows the president to "reserve parcels of land as a part of the national monuments" that are "confined to the smallest area compatible with the proper care and management of the objects to be protected."
The Act's use of phrase "lands owned OR controlled" rather than "owned AND controlled" allows the president to declare a monument essentially at their sole discretion on any lands within the territorial United States, even on and encompassing privately held lands (given that the Property Clause of the U.S. Constitution which specifically directs that "The Congress will have the Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States.”).
The purpose of the Act is to protect the objects located within these "reserved lands." Legal scholars have speculated that it is possible for a president to simply declare a monument without exercising the reservation power, as a symbolic gesture. However, this has never been done. In the case of Pullman, approximately 203 acres encompassing both North and South Pullman have been reserved by President Obama with the "National Monument Boundary." These lands are now to be managed as part of the National Park System and any "historic resources" situated upon these lands must be preserved "unimpaired."
President Theodore Roosevelt declared Devil's Tower in Wyoming first national monument in the United States using the newly created authority of the Antiquities Act in 1906.