Of the many powers granted to the President of the United States, one of the most impactful is the ability to designate an area a national monument. The Antiquities Act of 1906 gave the president this power, and it has been used 121 times since then, averaging over one new national monument dedicated for every year the act has been in place. Whereas wilderness designation requires congressional approval, the president can unilaterally create a national monument, and conservationists are increasingly seeing this as a stepping stone to eventual wilderness protection, the most stringent of our land use protections.
Notably, President Barack Obama has made extensive use of the Antiquities Act, more so than any previous president. In all, he has created or expanded 23 national monuments during his two terms, protecting over 2 million acres of public land. Most recently, on February 12, 2016, President Obama designated three new national monuments in the deserts of southwestern United States, Sand to Snow, Mojave Trails, and Castle Mountains.
National monuments can be historical sites, large tracts of open land, and even old military installations. They are managed by different government agencies, but the majority are managed by the National Park Service.