Cal. Pub. Util. Code § 30636.2

In planning the development of a rapid transit system or any part thereof within its territory and in carrying out the provisions of Section 30001, the district may extend its studies to include any city or unincorporated area not within the territory of the district. The district may invite the participation in such studies of government agencies having planning jurisdiction in such extended areas, and the studies shall be coordinated with regional comprehensive and transportation planning programs. The district may accept and use for the purpose of rapid transit planning in such extended areas any funds provided for such purpose.