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.