Cal. Wat. Code § 51612.5
The county treasurer, at least 60 days prior to the expiration of the redemption period, shall give notice by registered mail of the fact of sale, the purchase price paid, the date of termination of the redemption period, and the fact that a failure to redeem by payment of the purchase price plus interest following the date of the sale, and plus costs incurred as a result of the sale to the county treasurer within the redemption period will result in permanent loss of the property by issuance of a treasurer's deed. The notice shall be mailed to the owner's last known address as shown on the last equalized county assessment roll. The notice shall also be mailed to any other person or entity holding an interest in the parcel requesting notice by written instrument identifying the parcel filed with the district office, and mailed to the address specified in the request. The district may impose a charge for each request.
Notwithstanding Section 51646, if the county treasurer fails to give the notice, the redemption period set forth in Section 51646 shall be extended to the date 60 days following the date of mailing of the notice in the manner provided for in this section.
Ca. Water Code § 51612.5