California Code, Health and Safety Code - HSC § 6830

(a) Any territory contiguous to the district.

(b) Any territory any point of which touches any point of the district.

(c) Any territory separated from the district by a “separating barrier,” which term includes a street, road, highway, railway line, railway crossing, railway right-of-way, watercourse, lagoon, or other natural barrier.

(d) Any territory not contiguous to the district that will, in the opinion of the district board, be benefited by inclusion in the district.

Any territory specified in this section may consist of one or more separate parcels of land, but it is not necessary that all parcels shall constitute in the aggregate one tract of land.