CAL. CCP. CODE § 2017.010 : California Code - Section 2017.010

Unless otherwise limited by order of the court in accordance with this title, any party may obtain discovery regarding any matter, not privileged, that is relevant to the subject matter involved in the pending action or to the determination of any motion made in that action, if the matter either is itself admissible in evidence or appears reasonably calculated to lead to the discovery of admissible evidence. Discovery may relate to the claim or defense of the party seeking discovery or of any other party to the action. Discovery may be obtained of the identity and location of persons having knowledge of any discoverable matter, as well as of the existence, description, nature, custody, condition, and location of any document, electronically stored information, tangible thing, or land or other property.