California Code, Government Code - GOV § 65919.4

(a) Not later than the date the county notices the public hearing on a proposed action before the county planning commission, the county shall notify an affected city of the nature of the proposed action.

(b) Not later than the date the city notices the public hearing on a proposed action before the city planning commission, the city shall notify the county of the nature of the proposed action.

(c) The information in the notification shall not be less than the information contained in the notice of public hearing. The notification required by this section and by Section 65919.8 shall be given by first-class mail or by hand delivery.The notice shall also indicate the earliest date on which the board of supervisors or city council, as the case may be, can act on the proposed action or the modification to the proposed action.