California Code, Code of Civil Procedure - CCP § 801.11

On the trial of the action, the court shall determine the rights of all the parties thereto and shall require proof of the facts alleged. Any certificate issued on sale made to satisfy any public improvement assessment or any bond issued to represent such assessment shall be presumed to have been paid and redeemed where no deed pursuant thereto has been issued and such sale was made more than four years prior to the commencement of the action.

The presumption herein mentioned shall become and be conclusive if no deed pursuant to such sale is issued within four years after the date of sale or prior to January 1, 1953, whichever is the later; and no public official shall thereafter execute or issue any deed pursuant to such sale.