[UPDATE: And here's a different angle, from the now-defunct part of the Bay Bridge.]
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.