President Bill Clinton designated the monument in 1996 under the Antiquities Act of 1906, which allows a president to “declare by public proclamation historic landmarks.” We contend that President Trump exceeded the authority of the Antiquities Act, because the Act does not allow a succeeding president to strip that designation. Because President Trump was not delegated the authority to shrink a national monument, he also violated the Property Clause of the Constitution, which gives Congress sole authority to set the rules and regulations regarding public lands. Congress enacted the Antiquities Act to provide protections for the nation’s significant and diverse historic, cultural, and scientific heritage. The area comprising the original monument designation of almost two million acres hosts a wealth of archaeological and historical sites, critical habitat for a wide array of plant and animal species, and diverse recreational opportunities. President Trump’s reduction of Grand Staircase-Escalante National Monument is illegal and a potentially immense loss for our nation.