Cal. Pub. Res. Code § 9506

The board of supervisors of each county in which there lies any portion of the district shall, annually, at the time of levying county taxes, levy an assessment on the land exclusive of improvements, trees, and mineral rights, within the county and within the district to be known as the “ ____ (name of district) Resource Conservation District assessment,” sufficient to raise the amount reported to them in the estimate of the directors.