Cal. Commercial Code § 2205

(a) An offer by a merchant to buy or sell goods in a signed record which by its terms gives assurance that it will be held open is not revocable, for lack of consideration, during the time stated or if no time is stated for a reasonable time, but in no event may such period of irrevocability exceed three months; but any such term of assurance on a form supplied by the offeree must be separately signed by the offeror. (b) Notwithstanding subdivision (a), when a merchant renders an offer, oral or written, to supply goods to a contractor licensed pursuant to the provisions of Chapter 9 (commencing with Section 7000) of Division 3 of the Business and Professions Code or a similar contractor’s licensing law of another state, and the merchant has actual or imputed knowledge that the contractor is so licensed, and that the offer will be relied upon by the contractor in the submission of its bid for a construction contract with a third party, the offer relied upon shall be irrevocable, notwithstanding lack of consideration, for 10 days after the awarding of the contract to the prime contractor, but in no event for more than 90 days after the date the bid or offer was rendered by the merchant; except that an oral bid or offer, when for a price of two thousand five hundred dollars ($2,500) or more, shall be confirmed in a record by the contractor or the contractor’s agent within 48 hours after it is rendered. Failure by the contractor to confirm the offer in a record shall release the merchant from the merchant’s offer. Nothing in this subdivision shall prevent a merchant from providing that the bid or offer will be held open for less than the time provided for herein.