California Code, Code of Civil Procedure - CCP § 325

(a) For the purpose of constituting an adverse possession by a person claiming title, not founded upon a written instrument, judgment, or decree, land is deemed to have been possessed and occupied in the following cases only:

(b) In no case shall adverse possession be considered established under the provision of any section of this code, unless it shall be shown that the land has been occupied and claimed for the period of five years continuously, and the party or persons, their predecessors and grantors, have timely paid all state, county, or municipal taxes that have been levied and assessed upon the land for the period of five years during which the land has been occupied and claimed. Payment of those taxes by the party or persons, their predecessors and grantors shall be established by certified records of the county tax collector.