California Code, Health and Safety Code - HSC § 40911

(a) Except as provided in subdivision (b), each district which has been designated a nonattainment area for state ambient air quality standards for ozone, carbon monoxide, sulfur dioxide, or nitrogen dioxide shall prepare and submit a plan for attaining and maintaining the standards to the state board not later than December 31, 1990.

(b) Notwithstanding subdivision (a), any district which is a receptor or contributor of transported air pollutants, as determined by the state board pursuant to subdivision (a) of Section 39610, shall prepare and submit its plan to the state board not later than June 30, 1991.