(covers information from several alternate timelines)
Oakland was a city located in the San Francisco Metropolitan Area, California.
In 1941, a poster for boxing listed matches in this city. The headline match was between DeWaay and Johnson. (TNG: "The Big Goodbye")
In 1986, its location was labeled on a San Francisco Municipal Railway system map. In the late 20th century, Oakland was the site of two military bases: the Oakland Army Base and the Oakland Supply Depot. This city was connected to San Francisco by the San Francisco-Oakland Bay Bridge. (Star Trek IV: The Voyage Home)
In 2151, an artist in Oakland was awaiting a decent photograph of Captain Jonathan Archer in order to paint Archer's portrait, which would in turn be hung on the wall in Starfleet Command in the captain's honor. (ENT: "Rogue Planet")
In an alternate 2404, Admiral Kathryn Janeway appropriated SC-4 from the Oakland Shipyard. (VOY: "Endgame")