California Code, Code of Civil Procedure - CCP § 360

No acknowledgment or promise is sufficient evidence of a new or continuing contract, by which to take the case out of the operation of this title, unless the same is contained in some writing, signed by the party to be charged thereby, provided that any payment on account of principal or interest due on a promissory note made by the party to be charged shall be deemed a sufficient acknowledgment or promise of a continuing contract to stop, from time to time as any such payment is made, the running of the time within which an action may be commenced upon the principal sum or upon any installment of principal or interest due on such note, and to start the running of a new period of time, but no such payment of itself shall revive a cause of action once barred.