Bunkers on the Marin Headlands, overlooking San Francisco, described by Nick Villa of the Golden Gate Raptor Observatory, "Those doors lead into the bunkers where the USA army stored their ordanance and powder for the big guns. At the back of those bunkers is an airshaft going up at least five stories to one of the ocean facing gun emplacements. The rusting rails above the doors had runners on them to haul out the shells which weighed several hundred pounds. There they were loaded on trucks and brought directly to the gun emplacements via the now abandoned roads. The largest guns only fired once placing a practice round just beyond the Faralon Islands. The shell was 18.2 inches in diameter and probably weighed as much as a Volkswagon. Today, they're used to store our lure bird food and various other supplies. "