Cal. Health and Safety Code § 39606.1

(a) On or before January 1, 1997, the state board shall adopt regulations to designate, and determine the boundaries of, an air basin known as the Mojave Desert Air Basin. The air basin shall have a territory that is based upon similar meteorological and geographical conditions and consideration for political boundary lines. The air basin shall consist of at least all of the following: (1) The desert portions of Los Angeles County that, immediately prior to the date of the adoption of the regulations, were within the Southeast Desert Air Basin. (2) The desert portions of Kern County that, immediately prior to the date of the adoption of the regulations, were within the Southeast Desert Air Basin. (3) Any portion of the Mojave Desert Air Quality Management District that, immediately prior to the date of the adoption of the regulations, was within the Southeast Desert Air Basin. (4) Any other area contiguous to the areas indicated in paragraphs (1) to (3), inclusive, that the state board determines by a preponderance of the evidence is appropriate for inclusion. (b) Areas that, immediately prior to the date of the adoption of the regulations, were within the Southeast Desert Air Basin and are not included in the Mojave Desert Air Basin shall remain in the Southeast Desert Air Basin, subject to Section 39606.