More than 2,400 Marines and civilians biked 56-miles through base during the Ironman 70.3 Oceanside, Calif. triathlon March 30. The competitors swam 1.2-miles in the Oceanside Harbor, pedaled through base and ran 13.1-miles through the coastal streets of Oceanside. - More than 2,400 Marines and civilians biked 56-miles through base during the Ironman 70.3 Oceanside, Calif. triathlon March 30. The competitors swam 1.2-miles in the Oceanside Harbor, pedaled through base and ran 13.1-miles through the coastal streets of Oceanside.