Seems it was an alligator lizard, a species native to northern California. They _can_ bite, so I guess I'm glad this one didn't.
The California Herps website www.californiaherps.com has some good information and lots of clear photos. This shot of a San Francisco alligator lizard (note that this one is brown, while the one I saw was quite greenish) was taken by Gary Nafis.
If I ever see another one in a space as unsuitable as a parking lot, I will capture it, put it in a safe container overnight, and drop it off in Golden Gate park or somewhere similar, free of cars.