Cal. CIV § 1633.5

(a) This title does not require a record or signature to be created, generated, sent, communicated, received, stored, or otherwise processed or used by electronic means or in electronic form.

(b) This title applies only to a transaction between parties each of which has agreed to conduct the transaction by electronic means. Whether the parties agree to conduct a transaction by electronic means is determined from the context and surrounding circumstances, including the parties’ conduct. Except for a separate and optional agreement the primary purpose of which is to authorize a transaction to be conducted by electronic means, an agreement to conduct a transaction by electronic means may not be contained in a standard form contract that is not an electronic record. An agreement in such a standard form contract may not be conditioned upon an agreement to conduct transactions by electronic means. An agreement to conduct a transaction by electronic means may not be inferred solely from the fact that a party has used electronic means to pay an account or register a purchase or warranty. This subdivision may not be varied by agreement.

(c) A party that agrees to conduct a transaction by electronic means may refuse to conduct other transactions by electronic means. If a seller sells goods or services by both electronic and nonelectronic means and a buyer purchases the goods or services by conducting the transaction by electronic means, the buyer may refuse to conduct further transactions regarding the goods or services by electronic means. This subdivision may not be varied by agreement.

(d) Except as otherwise provided in this title, the effect of any of its provisions may be varied by agreement. The presence in certain provisions of this title of the words “unless otherwise agreed,” or words of similar import, does not imply that the effect of other provisions may not be varied by agreement.