There are several Renaissance Faires and or historical period Faires in northern California. The Merrie Pryanksters notably attend many faires as an acting or performing troupe.
Northern California Renaissance Faire
Once upon a time this Faire was held in Novato. The Novato location was nestled back into a wooded valley trail that gave the Faire a more authentic feel.
Then it was moved to Vacaville for several years. It was located near The Nut Tree. There wasn't the same "removed from reality" feel due to the proximity of the Nut Tree airport and Interstate 80. The faire at Casa de Fruita, close to Hollister, is a lineal descendent of that Faire, but is run by different folks. It is adjacent to State Hwy. 152, but most of the site is sufficiently buffered and achieves some "distance from reality."
Folsom Renaissance Faire
Cameron Park Lake Renaissance Tudor Fayre
If you'd like to go to more Renaissance Faires, have an interest in old English folk music and folk dance, and can make it to campus on Thursday evenings, you might want to check out the English Country Dancers.
If you like recreating history, from doing arts and science projects like weaving and dying authentic fabrics, to getting in armor, learning to fight with sword and shield and participating in large battles, check out the Society for Creative Anachronism.