Yes indeed, San Francisco County covers a lot of territory. It even stretches across the bay to Alameda Island. Check the Wiki, which is almost always correct:
“Several islands—Alcatraz, Treasure Island, and the adjacent Yerba Buena Island, and small portions of Alameda island, Red Rock Island, and Angel Island are part of the city.”
So, here it is, from Twin Peaks. The foreground shows the eastern part of S.F. and the background shows where San Francisco has a sliver of the old Alameda Naval Air Station. It’s the area right by the boat, see? If there’s a fire there, that would be the responsibility of San Francisco. I’m seriously.
Click to expand.
Here’s a map showing the county line on Alameda in white. And Google shows where they stopped building a landfilled peninisula to the north of the NAS, so as to not encroach upon the City and County of San Francisco.
[UPDATE: Some better photos are here, under Category #4. The SFFD reference below has to do with something I saw in an SFFD manual, but yes, prolly firefighters in Alameda would help us out in an emergency. This shot from a different angle, from the now-defunct part of the Bay Bridge, shows things well. And yes, as Redditor Eugene says, the military went hog-wild with landfill and went over the pre-existing Alameda/San Francisco border. Like who was going to stop them?]