Let's clear something up right away. You get to visit San Francisco, you have (as in a distasteful obligation) to visit L.A. And you have my sympathies for that.Irish Music in San Francisco: The Plough and Stars, The Front Room (occasionally), and An Bodhran.
Across the Bay in Oakland: The Starry Plough
These places all serve a good pint and the craic can be fierce.
Don't know about L.A.