Cal. Code of Civil Procedure § 2033.420

(a) If a party fails to admit the genuineness of any document or the truth of any matter when requested to do so under this chapter, and if the party requesting that admission thereafter proves the genuineness of that document or the truth of that matter, the party requesting the admission may move the court for an order requiring the party to whom the request was directed to pay the reasonable expenses incurred in making that proof, including reasonable attorney’s fees. (b) The court shall make this order unless it finds any of the following: (1) An objection to the request was sustained or a response to it was waived under Section 2033.290. (2) The admission sought was of no substantial importance. (3) The party failing to make the admission had reasonable ground to believe that that party would prevail on the matter. (4) There was other good reason for the failure to admit.