California Code, Harbors and Navigation Code - HNC § 6216

The board of supervisors may make such changes in the proposed boundaries of the district as are advisable, and it shall define and establish the boundaries.

If the board of supervisors deems it proper to include any territory not included within the boundaries proposed in the petition, it shall first give notice of its intention so to do, by publication of notice in a newspaper published in the county in which the district is located, for two times.  The hearing on a proposed inclusion of additional territory shall not be continued beyond sixty days after the board determines to give notice of its intention to increase the boundaries.  Within ten days of the final hearing of the matter, the board of supervisors shall make its order fixing the boundaries of the district.