California Code, Code of Civil Procedure - CCP § 1240.140

(a) As used in this section, “public agencies” includes all those agencies included within the definition of “public agency” in Section 6500 of the Government Code.

(b) Two or more public agencies may enter into an agreement for the joint exercise of their respective powers of eminent domain, whether or not possessed in common, for the acquisition of property as a single parcel. Such agreement shall be entered into and performed pursuant to the provisions of Chapter 5 (commencing with Section 6500) of Division 7 of Title 1 of the Government Code.