Two University of Oklahoma student-athletes are among the U.S. contingent headed to Guanajuato, Mexico, for the bi-annual North American, Central American and Caribbean (NACAC) Under-23 Track and Field Championships held July 6-8.OU's George Alex, who exhausted his collegiate eligibility this season, and senior-to-be Riley Masters will compete for Team USA in distance running events.Alex will run the 5,000 meters and Masters the 1,500 meters, the same events the two competed at the recent U.S. Olympic Trials in Eugene, Ore.