Cal. CCP § 1255.250

(a) If the amount originally deposited is increased pursuant to Section 1255.030 and the total amount sought to be withdrawn exceeds the amount of the original deposit, the applicant, or each applicant if there are two or more, shall file an undertaking. The undertaking shall be in favor of the plaintiff and shall secure repayment of any amount withdrawn that exceeds the amount to which the applicant is entitled as finally determined in the eminent domain proceeding, together with interest as provided in Section 1255.280. If the undertaking is executed by an admitted surety insurer, the undertaking shall be in the amount by which the total amount to be withdrawn exceeds the amount originally deposited. If the undertaking is executed by two or more sufficient sureties, the undertaking shall be in double such amount, but the maximum amount that may be recovered from such sureties is the amount by which the total amount to be withdrawn exceeds the amount originally deposited.

(b) If there are two or more applicants, the applicants, in lieu of filing separate undertakings, may jointly file a single undertaking in the amount required by subdivision (a).