California Code, Health and Safety Code - HSC § 40963

(a) The Sacramento district board may, by resolution, include all or a portion of the County of Placer within the Sacramento district, upon receipt of a resolution from the board of supervisors of the county requesting inclusion and specifying the portion of the county to be included in the Sacramento district. All territory included within the Sacramento district shall be contiguous.

(b) The inclusion of any county, or portion thereof, in the Sacramento district shall become effective on the July 1 immediately following the adoption of the resolution of inclusion by the Sacramento district board.

(c) A copy of the resolution of inclusion shall be transmitted by the Sacramento district board to the board of supervisors and to the state board.