	Introduction

Beginning with President Theodore Roosevelt, Presidents have protected well over 100 areas under the Antiquities Act of 1906. These protected areas, totaling hundreds of millions of acres of land as well as large marine areas, are known as national monuments. However, it appears that presidential authority may be more constrained, although it remains unresolved whether a President could lawfully abolish, or the extent to which a President could significantly diminish, a previously proclaimed national monument. The act provides, in part: 
(a) Presidential Declaration.—The President may, in the President's discretion, declare by public proclamation historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest that are situated on land owned or controlled by the Federal Government to be national monuments. However, a number of legal analyses, since at least the Franklin Roosevelt Administration, have agreed that a presidential proclamation of a national monument under the Antiquities Act may be undone only by Congress. Some more modern analysts also have asserted that the President lacks authority to undo a national monument proclamation under the Antiquities Act. However, given the silence of the Antiquities Act on this specific question, as well as the potential analogy to other presidential executive orders and proclamations, the existence or scope of a President's authority to abolish national monuments is still a matter of debate that has not been squarely resolved. However, the 1938 Attorney General opinion discussed above contemplates reduction of monuments in size pursuant to the "smallest area" language: 
While the President from time to time has diminished the area of national monuments established under the Antiquities Act by removing or excluding lands therefrom, under that part of the act which provides that the limits of the monuments "in all cases shall be confined to the smallest area compatible with the proper care and management of the objects to be protected," it does not follow from his power so to confine that area that he has the power to abolish a monument entirely. On the other hand, not all management details are contained in a national monument proclamation. FLPMA expressly prohibits the Secretary of the Interior from modifying or revoking any withdrawal creating national monuments under the Antiquities Act. Congressional Authority Over National Monuments

Congress can establish national monuments on federal land primarily pursuant to its authority under the Property Clause of the U.S. Constitution, which states: "The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States."
The Antiquities Act of 1906 authorizes the President to declare, by proclamation, that objects of historic or scientific interest on federal lands are designated as national monuments. Over the course of more than a century, Presidents have cited the Antiquities Act as authority for protecting well over 100 land and marine areas, totaling hundreds of millions of acres, as national monuments. National monuments generally are reserved and protected from certain uses such as mineral leasing or mining, although management terms may vary by monument. Partly because of such restrictions, some presidential proclamations of national monuments—and proposals for such proclamations—have led to controversy.
Once a President has proclaimed a national monument on federal land, later Presidents or Congresses may want to abolish, diminish, or otherwise change the monument. Congress has clear authority to do so, largely under the Property Clause of the U.S. Constitution, which provides that "Congress shall have Power to ... make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States." Congress has used its authority to abolish or to remove acreage from national monuments on several occasions.
It appears that presidential authority may be more constrained. No President has ever abolished or revoked a national monument proclamation, so the existence or scope of any such authority has not been tested in courts. However, some legal analyses since at least the 1930s have concluded that the Antiquities Act, by its terms, does not authorize the President to repeal proclamations, and that the President also lacks implied authority to do so. Under this view, once a President has applied the Antiquities Act to protect objects of historic or scientific interest, only Congress can undo that protection. On the other hand, Presidents have deleted acres from national monuments, proclaiming that the deleted acres do not meet the Antiquities Act's standard that the protected area be the "smallest area compatible with the proper care and management of the objects to be protected." Presidents also can modify the management of national monuments, although the outer boundaries of this authority, too, appear to be untested. Under the Federal Land Policy and Management Act of 1976 (FLPMA), executive branch officials other than the President are barred from modifying or revoking any withdrawal creating national monuments under the Antiquities Act.