Legal Question in Personal Injury in California

Jurisdiction is valid in any county in which one or more of the defendants reside or where the cause of action arose. Since you asked this as a personal injury question, proper venue would most likely be the county in which the injury occurred, although venue is more flexible than jurisdiction since it is focused on the "best" place to try the case from the available choices of counties with jurisdiction. Best being a practical consideration based on where the parties and evidence and witnesses are all located and what would be the most convenient or least inconvenient county among those that have jurisdiction.