Cal. Pub. Res. Code § 5524

The board of supervisors of the county having the largest area within the district shall cause a certified copy of the order declaring the district created and established, declaring the result of the election, and describing the boundaries of the district, to be recorded with the county recorder of each county in which any portion of the district is situated, and a certified copy shall be filed in the office of the Secretary of State. Thereupon the creation and establishment of the district is complete, and the persons elected as directors shall enter immediately upon their official duties after qualifying according to law.