'Determination of the relevant product and geographic markets is a necessary predicate to deciding whether a merger contravenes the Clayton Act.' Marine Bancorporation, 418 U.S. at 618 (internal quotation marks omitted). Definition of the relevant market is a factual question 'dependent upon the special characteristics of the industry involved and courts will not disturb such findings unless clearly erroneous.' Twin City Sportservice, Inc. v. Charles O. Finley & Co., 676 F.2d 1291, 1299 (9th Cir. 1982).