By definition, a national monument preserves the unique natural, historic or cultural heritage of public lands. National monuments are created by Congressional legislative action or by Presidential Proclamation using the Antiquities Act of 1906.
The Mojave Trails National Monument was created by Presidential Proclamation, joining a list of 15 other monuments in the state of California. Spanning 1.6 million acres, more than 350,000 acres of previously congressionally designated Wilderness, the Mojave Trails National Monument is under the administrative oversight of the Bureau of Land Management. They are required to develop a management plan for the monument.