California Code, Code of Civil Procedure - CCP § 2035.010

(a) One who expects to be a party or expects a successor in interest to be a party to an action that may be cognizable in a court of the state, whether as a plaintiff, or as a defendant, or in any other capacity, may obtain discovery within the scope delimited by Chapter 2 (commencing with Section 2017.010), and subject to the restrictions set forth in Chapter 5 (commencing with Section 2019.010), for the purpose of perpetuating that person's own testimony or that of another natural person or organization, or of preserving evidence for use in the event an action is subsequently filed.

(b) One shall not employ the procedures of this chapter for purposes of either ascertaining the possible existence of a cause of action or a defense to it, or of identifying those who might be made parties to an action not yet filed.