Ariz. Rev. Stat. § 48-3012
If the district has been divided into divisions by the board of supervisors, the board of directors by an order entered in its proceedings not less than thirty days prior to the first district election shall establish, define and divide the district into three divisions as nearly equal in acreage as practicable to be known and designated as division no. one, division no. two and division no. three. In addition to any directors elected at large, and except as provided by section 48-2914, each division shall be represented by one director on the board, and unless the acreage of the division is substantially changed by the inclusion or exclusion of district lands, the divisions shall remain as so established. If a substantial change is made by such inclusion or exclusion, the board of directors shall redivide the district and define new divisions thereof, maintaining in the redivision as nearly as practicable the boundaries of each division as formerly established. Notice of such redivision shall be included in the notice of the next regular election.
A.R.S. § 48-3012