Mexican Era, 1822-1846
Although Spain had anticipated an attack on the pueblo on San Francisco Bay by the British, that assault was never realized. Ironically, the greatest threat to Spain's control of the region came from an unforeseen enemy which had also been a former ally. The Spanish colony of Mexico embarked on a war for independence in 1821. Following a successful revolt later that year, the Colony won its freedom from Spain. Alta California, which encompasses present-day California, passed quietly into Mexican control.
Augmenting the fortification of the San Francisco Bay was a low priority for the new regime, and the defenses at Bateria Yerba Buena soon fell into further disrepair. A U.S. military report issued in 1841 revealed that only one rusty cannon was stationed at the derelict battery, and by 1846 the coastal fortifications at Bateria Yerba Buena were entirely abandoned by the Mexican military forces. At the present time, no remains of this outpost are known to exist.
In 1834, General Mariano Guadalupe Vallejo, who was the new comandante of the Presidio, moved part of the San Francisco garrison north to Sonoma. The move was partially precipitated by the dilapidated condition of the Presidio's adobe structures. The damage to the fort's structures, largely as a result of adverse weather conditions, was so severe that the fort needed to be almost entirely rebuilt. However, the Mexican government refused to fund the project and the Presidio continued to deteriorate. By 1835, Vallejo had transported the last of the San Francisco garrison to the new northern outpost in Sonoma, leaving the security of the Presidio in the hands of a few caretakers.1
During the period of Mexican control of California, the increasing prominence in sea commerce and an expanding migration of Anglo-American settlers into the region had aroused the territorial ambitions of the United States. In June of 1846, American settlers, supported by a contingent of indigenous Californians, revolted against the Mexican government of Alta California in a movement known as the Bear Flag Revolt. The United States backed the insurgents, which dispatched a small force to march south from Sonoma. The revolt was led by a Captain of Topographical Engineers, John C. Fremont, and included mountain man Christopher "Kit" Carson.
Only meeting light resistance on their march to the pueblo of Yerba Buena, Fremont and his men quickly reached the mouth of the San Francisco Bay, and crossed the harbor at its narrowest point (the Spanish called the entry to the bay Boca del Puerto de San Francisco, but in the following years Fremont used his influence as a topographer to rename the harbor's entrance Chrysoceras or Golden Gate, when translated from Latin into English). When the American force reached the shores of Yerba Buena, the few Mexican soldiers stationed at the Presidio fled at the sight of Fremont's men, leaving the Castillo de San Joaquin and the Presidio effectively abandoned. Just two hours after the Americans landed on Yerba Buena, the entire arsenal of the Castillo, comprised of a number between ten and fourteen cannons, was rendered useless by a process known as "spiking."
The final assault on the Presidio came on July 9, 1846, when Captain John B. Montgomery of the U.S. sloop Portsmouth landed a force of marines to seize the settlement of Yerba Buena, which would later become known as San Francisco. At the Castillo de San Joaquin, the marines found three brass guns that they believed to be 12 and 18 pounders, made in 1623, 1628, and 1693. In addition, seven iron guns were found at the Castillo. The bronze guns that were recovered are believed to be the San Pedro, San Domingo, and La Birgen de Barbaneda. These guns are currently on display at the Presidio.