California Code, Streets and Highways Code - SHC § 10419

The person applying for a deed shall file with the tax collector an affidavit or affidavits showing that notice of such application has been given as required in this chapter, and if the notice was not served on the owner of the property personally that due diligence was used to find the owner. The affidavit or affidavits shall be filed by the tax collector in his office.