California Code, Streets and Highways Code - SHC § 5838

The board of supervisors shall cause notice of the time, place, and purpose of the hearing to be given by mail to each owner whose name and address appears on the last equalized assessment roll and who owns real property within the boundaries of the territory sought to be annexed.  The notice shall contain the name and telephone number of a local department or agency designated by the board of supervisors to answer inquiries regarding the hearing proceedings.  The person directed by the board of supervisors to mail the notices shall file, upon the completion of the mailing, an affidavit setting forth the time and manner of the compliance with this section.

In addition, the board of supervisors shall cause notices of the hearing to be posted in three conspicuous places within the territory proposed to be annexed.

The notices shall be headed “Notice of hearing” in letters not less than one inch in height and shall contain a description of the territory proposed to be annexed and a statement of the time and place of the hearing.  In lieu of the description the boundaries of territory proposed to be annexed may be shown by means of a diagram printed upon the notice.  The notice shall be posted not less than 10 days prior to the date set for the hearing.

In proceedings for annexation to sewer, lighting, or drainage maintenance districts, the board of supervisors shall direct its clerk to publish a notice once a week for two successive weeks in the newspaper of general circulation that the board deems most likely to give notice of hearing to the inhabitants.  Such notice shall state the time and place of the hearing and shall contain a description of the territory proposed to be annexed or, in lieu of such description, the boundaries of the territory proposed to be annexed may be shown by means of a diagram.  Such publication together with the posting of notices of hearing may be deemed adequate notice and no mailed notice need be required.