California Laws|Section 676.6.

                                                
676.6.  
(a) A person may assert a claim in a specified foreign money. If a foreign-money claim is not asserted, the claimant makes the claim in United States dollars. 
(b) An opposing party may allege and prove that a claim, in whole or in part, is in a different money than that asserted by the claimant. 
(c) A person may assert a defense, setoff, recoupment, or counterclaim in any money without regard to the money of other claims. 
(d) The
  determination of the proper money of the claim is a question of law.