CA Water Code Section 52750

When the sinking fund contains at least ten thousand dollars ($10,000), the county treasurer shall, upon request of the board, by notice published once a week for two successive weeks in some newspaper published in the county where the office of the district is located and, in its discretion, in any other newspaper, invite sealed proposals for the sale to the district of any of its outstanding bonds or refunding bonds secured by the assessment out of which the sinking fund was created.