Cal. Rev. & Tax. Code § 60503

(a) The certificate to be provided to the ultimate vendor consists of a statement that is signed under penalty of perjury by a person with authority to bind the buyer. A new certificate shall be given if any information in the current certificate changes. The certificate may be included as part of any business records normally used to document a sale. The certificate expires on the earliest of the following dates:
1. (1) The date one year after the effective date of the certificate.
2. (2) The date a new certificate is provided to the seller.
(b) An exemption certificate for diesel fuel used on a farm for farming purposes or for diesel fuel used in an exempt bus operation shall contain that information and be in the form as the board may prescribe.