I was visiting San Francisco and had a bit of extra time. Near the corner of Market and Castro I started walking around the neighborhood, just to see what was there.
I discovered a most amazing little park. It's tucked away in an obscure corner of the city, and it's dominated by a large, smoothly polished wall of rock. You sort of have to see it to believe it, but here are a few photos.
This is a section of the wall. The entire exposed wall is probably 100 feet long, and runs from ground level in the playground up about 50 or 60 feet, when it slopes away, turning into just an ordinary hillside.
Here's another, closer image. You can see how smooth the rock wall is polished--it even reflects the color of the sky here.
A last picture, just so you can be as amazed as I was.
So... what's the question? I want to learn more about this thing--but how?
This is clearly some kind of really interesting geological feature, and--darn it--I didn't have any geologists with me. I DO know that this rock is a kind of chert, and the rock face is highly polished. Maybe that will help you in searching.
What's the specific word (or search term) you want to find out more about the geology of.. this polished rock wall?
What's it called?
And... for extra credit, what's the address of this wall?