Cal. Civ. Proc. Code § 1240.610

Any person authorized to acquire property for a particular use by eminent domain may exercise the power of eminent domain to acquire for that use property appropriated to public use if the use for which the property is sought to be taken is a more necessary public use than the use to which the property is appropriated. Where property is sought to be acquired pursuant to this section, the complaint, and the resolution of necessity if one is required, shall refer specifically to this section.