Although not in San Francisco, there is a lab in Dublin, CA that I use:

Custom Photographic Services 6948-B Sierra Court Dublin, CA 94568 925/828-6000

CPS is an excellent all-around pro lab. They do about 95% of my work. Fast turnaround on E-6 processing of all sizes.

For processing & proofing color negatives I use:

E & J Photo Lab 7748 Dublin Blvd Dublin, CA 94568 925/829-0222

E&J seems to have a wider selection of papers & sizes for proofing than CPS. They also sell film, paper, albums, filing pages & a few other similar items. (Not broad in scope like a camera store.)