When did all this get started?

The law was enacted in 1906 to prevent looting of Indian artifacts from archaeological sites. The act has mostly been used since then by presidents to turn public land into national monuments protected forever from commercial development or future mineral exploitation.

It was in the news at the end of the Obama administration after President Barack Obama created several national monuments, setting aside millions of acres on land and sea. At the time, some Republicans in Congress said they wanted to reform the act, which they said encouraged federal government overreach, a claim that has dogged the law since it was adopted.

President Theodore Roosevelt, who signed the Antiquities Act into law, created 18 monuments, including the Grand Canyon and Olympic National Park in Washington, totaling more than a million acres. According to data from the National Park Service, fifteen other presidents from both parties have designated a total of 170 national monuments, including marine monuments.

The president can make national monuments only from land already controlled by the federal government, and the act generally does not change how the land is used, said Lisa Dale, the associate director of the Yale Center for Environmental Law and Policy. If leases for mining, ranching, drilling or logging already exist on land to be made into a national monument, they can continue, but new leases probably won’t be allowed, she said.

Most legal scholars and historians agree that the Antiquities Act does not give the president the authority to revoke previous national monument designations, but a president can change the boundaries of a national monument. Congress can convert a national monument into a national park, which it has done many times.