Gov. Code, § 66454

Any subdivider may file with a city the tentative map of a proposed subdivision of unincorporated territory adjacent to such city. The map, in the discretion of the city, may be acted upon in the manner provided in Article 2 (commencing with Section 66452) of this chapter, except that if it is approved, such approval shall be conditioned upon annexation of the property to such city within such period of time as shall be specified by the city, and such approval shall not be effective until annexation of such property to the city has been completed. If annexation is not completed within the time specified or any extension thereof, then the approval of such map by such adjacent city shall be null and void. No subdivision of unincorporated territory may be effected by approval of a map by a city unless annexation thereof to the city is completed prior to the approval of the final map thereof.