Cal. Water Code § 42293

At the conclusion of the hearing, the board shall by resolution determine whether the whole or only a portion of the district will be benefited by the project or unit. If the board determines that only a portion of the district will be benefited by the project or unit, the board may by resolution establish an improvement district consisting of that portion of the district. The resolution shall describe the territory within the improvement district in a manner sufficient for identification, and shall designate the improvement district by a distinctive name or number. In accordance with the resolution, said portion of the district shall thereupon constitute and be known as “____ Improvement District of ____ Water Storage District” or as “Improvement District No. ____ of ____ Water Storage District.”