Cal. Pub. Res. Code § 9481

The inclusion of additional lands in a district shall be made in accordance with the provisions of the District Reorganization Act of 1965, Division 1 (commencing with Section 56000) of Title 6 of the Government Code, except that unless otherwise provided in this chapter, the lands included in any district need not be contiguous but they shall be susceptible of the same general plan or system for the control of runoff, the prevention or control of soil erosion, and the development and distribution of water, or land improvement.