California Code, Civil Code - CIV § 1590

Where either party to a contemplated marriage in this State makes a gift of money or property to the other on the basis or assumption that the marriage will take place, in the event that the donee refuses to enter into the marriage as contemplated or that it is given up by mutual consent, the donor may recover such gift or such part of its value as may, under all of the circumstances of the case, be found by a court or jury to be just.