California Code, Civil Code - CIV § 1671

(a) This section does not apply in any case where another statute expressly applicable to the contract prescribes the rules or standard for determining the validity of a provision in the contract liquidating the damages for the breach of the contract.

(b) Except as provided in subdivision (c), a provision in a contract liquidating the damages for the breach of the contract is valid unless the party seeking to invalidate the provision establishes that the provision was unreasonable under the circumstances existing at the time the contract was made.

(c) The validity of a liquidated damages provision shall be determined under subdivision (d) and not under subdivision (b) where the liquidated damages are sought to be recovered from either:

(d) In the cases described in subdivision (c), a provision in a contract liquidating damages for the breach of the contract is void except that the parties to such a contract may agree therein upon an amount which shall be presumed to be the amount of damage sustained by a breach thereof, when, from the nature of the case, it would be impracticable or extremely difficult to fix the actual damage.