Donument Act This bill establishes the Southern Border Wall National Monument in the states of California, Arizona, New Mexico, and Texas to protect the southern border wall from alteration. The Bureau of Land Management (BLM) shall administer the monument. The BLM shall establish administrative jurisdiction over portions of the southern border wall within the monument as necessary to carry out this bill by entering into memoranda of understanding with each federal department or agency with administrative jurisdiction over land within the monument on which portions of the wall are located, and the governing body of each Indian tribe with administrative jurisdiction over land within the monument on which portions of the wall are located. The BLM shall prepare a general management plan for the monument.