“Included transit district” means any of the following which has operated a public transportation system since at least January 1, 1971:
(a) A transit district whose boundaries are contained entirely within those of a larger transit district.
(b) A district organized pursuant to Part 3 (commencing with Section 27000) of Division 16 of the Streets and Highways Code.
(Amended by Stats. 1972, Ch. 1408.)