Cal. Wat. Code § 46788.2
After the first publication of the notice required by Section 46788.1, and not less than 45 days nor more than 60 days before the date specified in that notice for the delivery of a deed, the county treasurer, or the district, if it was the purchaser, shall send by certified mail to each of the parties of interest, as specified in this section, at his or her last known address, a copy of the notice published pursuant to Section 46788.1. The county treasurer, or the district, if it was the purchaser, shall make a reasonable effort to ascertain the names and addresses of each of the parties of interest. For the purposes of this section, a "party of interest" is the holder of any interest in the delinquent property which would be terminated by execution and delivery of a deed.
Ca. Water Code § 46788.2