California
Code of Civil Procedure CCP § 2020.010
(a) Any of the following methods may be used to obtain discovery within the state from a person who is not a party to the action in which the discovery is sought:
(1) An oral deposition under Chapter 9 (commencing with Section 2025.010 ).
(2) A written deposition under Chapter 11 (commencing with Section 2028.010 ).
(3) A deposition for production of business records and things under Article 4 (commencing with Section 2020.410 ) or Article 5 (commencing with Section 2020.510 ).
(b) Except as provided in subdivision (a) of Section 2025.280 , the process by which a nonparty is required to provide discovery is a deposition subpoena.