Marine Corps Formal School instructors of the Marine Corps Mountain Warfare Training Center, Bridgeport, Calif., use an untouched slope of snow off their ski path to test for tell-tale signs of potential avalanche occurrence at the Leavitt Lake training area Jan 9. - Marine Corps Formal School instructors of the Marine Corps Mountain Warfare Training Center, Bridgeport, Calif., use an untouched slope of snow off their ski path to test for tell-tale signs of potential avalanche occurrence at the Leavitt Lake training area Jan 9.