California Code, Code of Civil Procedure - CCP § 1240.350

(a) Whenever a public entity acquires property for a public use and exercises or could have exercised the power of eminent domain to acquire such property for such use, the public entity may exercise the power of eminent domain to acquire such additional property as appears reasonably necessary and appropriate (after taking into account any hardship to the owner of the additional property) to provide utility service to, or access to a public road from, any property that is not acquired for such public use but which is cut off from utility service or access to a public road as a result of the acquisition by the public entity.

(b) Where property is sought to be acquired pursuant to this section, the resolution of necessity and the complaint filed pursuant to such resolution shall specifically refer to this section and shall include a statement that the property is necessary for the purpose specified in this section. The determination in the resolution that the taking of the substitute property is necessary has the effect prescribed in Section 1245.250.