Delighted to learn about this precursor to Bay Area foghorns - a fog cannon.
A bit of history: the first three lighthouses on the west coast (Alcatraz, Fort Point, and Point Bonita) were constructed in the 1850s in response to a whole bunch of gold rush era shipwrecks. At Point Bonita (which is at the mouth of the SF Bay), they initially constructed the lighthouse high on a hill above the ocean, which meant that it was often obscured in fog and thus not that effective as a lighthouse. To try and deal with that, they decided to add an auditory cue for ships navigating in high fog.
This took the form of a cannon that was to be fired every 30 minutes in dense fog. The picture above is Edward Maloney, the poor bastard tasked with manning the cannon. A few months after being hired to fire the fog cannon, Maloney was writing to the lighthouse board saying “I cannot find any person here to relieve me, not 5 minutes; I have been up 3 days and nights, and had only 2 hours rest.” Oof. To add insult to injury, it turned out that mariners couldn’t even hear the cannon from the water so the whole thing ended up being pretty much in vain. The fog cannon didn’t end up lasting long before being replaced with a bell and then later by steam powered fog signals. And they ended up moving the lighthouse to a better spot for visibility.