Here's the quick answer... It's a slickenside.
How did I find this? This wasn't a terribly hard problem. Here's how I approached it.
My initial query:
[ polished rock wall San Francisco ]
got me the street address (on Beaver Street, at the Corona Heights playground).
At this point I could use the Reverse Dictionary trick (see my earlier blog post), and that would work pretty well. Just go to a reverse dictionary such as One Look and do a query there on [ polished rock wall ] -- the second result is "slickenside," which is the correct answer.
But to do a regular Google search, I had to cast around a little bit until I found the query:
[ smooth polished rock surface ]
At which point I noticed the strange word "slickenside" -- when I read that article comparing glacial striations with polished rock surfaces, I quickly realized that this was exactly what I'd been seeing... right down to the parallel lines on the face of the rock.
To confirm this, however, I had to do one more search: I wanted to find the term "slickenside" used to describe the rock wall at the Corona Heights park. My verification query was
[ slickenside Corona Heights ]
which led me to a very nice article about the slickenside at the playground in the Corona Heights playground.
So there you go. Two different ways to approach this problem. The Reverse Dictionary method and finding another way to say "polished rock wall."
They both work just fine.
(And if you'd like to visit the slickenside in SF -- here's the Google Map link.)