The 49ers announced yesterday that they have signed running back Thomas Clayton to a contract. Terms of the deal were not disclosed. The 5-foot-11, 225-pound Clayton was taken in the sixth-round in April’s NFL Draft. The Kansas State product ran for 1,030 yards and seven touchdowns last season. According to the team’s web-site, the 49ers now have six of their nine draft picks under contract, including tackle Joe Staley, who was the second of the team’s two first-round selections.