Slabs of Mystery Traditional Geocache

Mysterious slabs of concrete, high on a hill, guard a drain. Was this part of a spillway for Elk Glen Lake, below?

Near the Golden Gate Park maintenance yard sits a set of tilted cement blocks. Lots of other rocks surround a drain. I wonder if it was, once, one of the old spillways that you run across in the park, some of which still function. No need to beat the bushes. You might want to picnic below this site. It's one of the quieter roads in the park.

$1 Legal Tender for FTF.

Note that this area will probably be inaccessible shortly before and after Outside Lands Event