The Mexican War was declared by the U.S. Congress on 11 May 1846 in response to a Mexican attack on U.S. troops in Texas. The declaration of war opened the door for American occupation of California. The American period began when American forces occupied San Diego in 1846. With end of the war, Mexico ceded all of upper California to the Americans in 1848 and a new round of land redistribution began.
On 19 Feb 1853, Archbishop Joseph Sadoc Alemany filed a claim on behalf of the Roman Catholic Church for the return of all former mission lands in the State of California. Ownership of 1,051 acres (for all practical intents being the exact area of land occupied by the original mission buildings, cemeteries, and gardens) was transferred back to the Catholic Church by land patents and proclamations signed by U.S. Presidents between 1855 and 1874.