Well, I got an answer back from somebody there about the St. Andrews State Park and it actually makes sense. (Thanks Todd at Red Alert Diving!) Apparently, my memory is slightly faulty as to the direction that the rock enclosed pool faced. It wasn't South. It was East. It's what is known now as The Kiddie Pool or Tidal pool. Per Todd: "The beach moved around it and changed it quite a bit". Then sometime in history, the Army Corp of Engineers must have pulled up a bunch of the boulders and moved them into piles inside the swim area as artificial reefs. On the satellite view, you can still see the remnants of the old wall. Now I know!