California's Three Feet for Safety Act requires drivers to leave a safe distance — generally at least three feet — when passing a cyclist, and to slow down where that is not possible. A driver who buzzes a rider, clips them, or forces them off the road has usually violated that duty.
When a close pass causes a crash, the passing rule can be central to fault. Even where no contact occurred, a driver whose unsafe pass forced a cyclist to crash may still be responsible, though those cases can be harder to prove and often turn on witnesses and video.
The exact requirement and how it applies to your crash are worth confirming, but the key point is that drivers do not get to treat a cyclist's space as optional. Passing too close is a breach of a specific safety duty, not just bad manners.