California Code, Streets and Highways Code - SHC § 5821.1

The board of supervisors may, in its resolution declaring its intention to order work done or improvements made, declare its intention to order the territory within which the work is to be done or improvements constructed annexed to an existing maintenance district formed under the provisions of this chapter or under the provisions of Chapter 4, Part 3, Division 5, of the Health and Safety Code.  1

The resolution of intention may describe the territory to be annexed as having the same boundaries as those of the district to be assessed for the cost of constructing the improvements.