California Code, Health and Safety Code - HSC § 44003

(a)(1) An enhanced motor vehicle inspection and maintenance program is established in each urbanized area of the state, any part of which is classified by the Environmental Protection Agency as a serious, severe, or extreme nonattainment area for ozone or a moderate or serious nonattainment area for carbon monoxide with a design value greater than 12.7 ppm, and in other areas of the state as provided in this chapter.

(2) A basic vehicle inspection and maintenance program shall be continued in all other areas of the state where a program was in existence under this chapter as of the effective date of this paragraph.

(c)(1) Districts classified as attainment areas may request the department to implement all or part of the program elements defined in this chapter. However, the department shall not implement the program established by Section 44010.5 in any area other than an urbanized area, any part of which is classified by the Environmental Protection Agency as a serious, severe, or extreme nonattainment area for ozone or a moderate or serious nonattainment area for carbon monoxide with a design value greater than 12.7 ppm.

(2) Districts that include areas classified as basic program nonattainment areas pursuant to subdivision (a) may, except as provided in paragraph (1), request the implementation in those areas of test procedures and equipment required for enhanced program areas and any other program requirement specified for enhanced program areas.