Paddle Monster Race Calendar This list includes a number of California races, but it does not tend to include many links for more information - so get the race name & date here then do an internet search with the name.
The California Gold more of a multi-leg surf life saving kind of race series/fund raiser (includes a surfski leg)
US Surfski Championships (facebook) held for many years in the San Francisco Bay area, the race there has been on hiatus for several years (with the Gorge Downwind Championship race standing in as the de facto US Championships)