Thanks to a tip from Steve, I headed down to Ocean Beach to check out reports of an 1800′s shipwreck being visible at low tide. Back in 1878, a clipper ship broke free from its anchor and ran aground on the beach right at the end of Noriega Street. Sure enough, there it was, although a little less glamorous than what I was expecting. The timbers of the ship can be seen peeking out of the sand.
Check out the SFGate article for more info. Check the Ocean Beach Bulletin for a few more photos.
UPDATE 05/20/11: Today, nearly the full length of the ship was visible. I arrived a bit after low tide and the ship was starting to be covered back up by the incoming water.