Cal. Sts. & High. Code § 27041

If only part of any county is proposed to be included in the district, the extent of the part of the county included may be indicated by naming the county and excepting therefrom some administrative or governmental subdivisions thereof, such as townships, school districts or other similar subdivisions, or the excluded portion may be described by its boundaries. In any description of included or excluded territory, reference to recorded instruments may be made for the purpose of defining boundaries.