Pentagram set in concrete

This is a pentagram set in concrete on the roof of a small building in Presidio Park near Old Town, San Diego. I believe this building is known as the Pattie Memorial, the Observation Deck, or the Witches Tower. You can see spilled candle wax in the middle, so I think it's safe to say there has been some spell casting there. No idea what this is doing very near the site of the oldest mission in San Diego.

Looking at Google Maps, you can clearly see that this building is 5 sided.