On January 30, 1847 the city of Yerba Buena, which means mint in Spanish was offically renamed the city of San Francisco.
Offical Documentation taken from the Museum of the City of San Francisco website (http://www.sfmuseum.org):
AN ORDINANCE WHEREAS, the local name of Yerba Buena, as applied to the settlement or town of San Francisco, is unknown beyond the district; and has been applied from the local name of the cove, on which the town is built: Therefore, to prevent confusion and mistakes in public documents, and that the town may have the advantage of the name given on the public map;
IT IS HEREBY ORDAINED, that the name of SAN FRANCISCO shall hereafter be used in all official communications and public documents, or records appertaining to the town.
Washington Bartlett, Chief magistrate
January 30, 1847