In an effort to strengthen the defenses of San Francisco Bay, Governor Diego de Borica decided to construct a battery to protect the quiet cove immediately to the east of Point Medanos (now known as Fort Mason). Since the Punta Medanos promontory commanded not only the cove but also the passage between the mainland and Alcatraz Island, it was chosen as the ideal spot to fortify. After being constructed between April and June of 1797, De Borica fortified the battery with five, eight-pounder brass cannons sent from Castillo de San Joaquin (at the present site of Fort Point), where they were deemed too small to be of use.1
The new installation was named Bateria San Jose but soon became known as Bateria de Yerba Buena. However, this fortification soon fell into disrepair. In 1806 Governor Arrillega's inspection of the fort reported that three of its five cannons were functional, and there was substantial damage to the battery structures. In 1822, after a successful Mexican revolt against the Spanish empire, the derelict Bateria de Yerba Buena came under the auspices of the Mexican government.2
1.John Phillip Langelier and Daniel Bernard Rosen, El Presidio de San Francisco: History under Spain and Mexico, 1776-1846. California: National Park Service, 1992.
2. Public Affairs Office, Western Area, Military Traffic Management and Terminal Service. The Story of Fort Mason: Historic U.S. Army post in San Francisco. California: National Park Service, 1971.