Who knew that the foggy city has magnificent sand dunes, up to 700 feet long and 30 feet high?
Nobody but us fishes, and a few octopi and friends, I guess, since the dunes are just outside the Golden Gate, under a couple hundred feet of water.
Another hidden surprise from the wonderful underwater world.
These are some of the largest underwater dunes on Earth, formed by the powerful Golden Gate tidal currents that routinely exceed 5 miles per hour, thanks to lots of water rushing in and out of a narrow bay mouth.
Add in a westerly wind at 25 mph (not unusual) and you get the lovable and intense "washing machine" conditions great for windsurfing under the Golden Gate bridge.