Cal. Civ. Proc. Code § 871.7

(a) This chapter does not apply where the improver is a public entity or where the improvement is made to land owned or possessed by a public entity. As used in this section, “public entity” includes the United States, a state, county, city and county, city, district, public authority, public agency, or any other political subdivision or public corporation.
(b) This chapter does not apply where the owner of the land upon which the improvement is constructed has appropriated the land to a public use and could have acquired the land for that use by exercising the power of eminent domain.