High Quality Content by WIKIPEDIA articles! Pacific Division of the U. S. Army was created on October 10, 1848, as the Army reorganized its administration for the new territories acquired during the Mexican American War. Military Department 10 (California) and Military Department 11 (Oregon Territory) were subordinated to the new Division that had its headquarters at Monterey. In June 1849 division headquarters moved to the California, for a month then moved to Benicia and the Benicia Arsenal in the upper San Francisco Bay in July 1849.