Cal. Health and Safety Code § 41503

(a) Within 12 months of receiving each district’s attainment plan developed pursuant to Section 40911, the state board shall determine whether the attainment date specified in the plan represents the earliest practicable date and whether the measures contained in the plan are sufficient to achieve and maintain state ambient air quality standards. (b) The state board shall conduct its review to include the plans of every district in the air basin, and shall determine whether the combination of measures in all the plans is sufficient to achieve and maintain state ambient air quality standards throughout the air basin. The state board shall hold at least one public hearing in each affected air basin prior to reaching a final determination of the sufficiency of the plans. The state board shall require control measures for the same emission sources to be uniform throughout the air basin to the maximum extent feasible, unless a district demonstrates to the satisfaction of the state board that adoption of the measure within its jurisdiction is not necessary to achieve or maintain the state ambient air quality standard. (c) Where air pollutant transport is a factor, the state board shall determine whether the attainment plan is sufficient to satisfy the requirements of Section 40912. (d) If a district is unable to specify an attainment date and the state board concurs that projecting an attainment date is not feasible, the state board shall determine whether the plan contains every feasible control strategy or measure to ensure progress toward attainment is maintained. (e) In making determinations under subdivisions (a), (b), (c), and (d), the state board shall consider any emission reductions occurring in, or expected to occur in, the district or air basin.