Rescuers were battling heavy snow to reach a Marine Corps helicopter carrying five troops that went down in a mountainous area outside San Diego. The aircraft was located Wednesday morning by civil authorities near the mountain community of Pine Valley, about a 45-mile drive from San Diego. But rescue crews said snowy conditions were making access challenging on the ground. The fate of those aboard wasn’t immediately known. Defense officials say the Marines were flying a CH-53E Super Stallion helicopter from Creech Air Force Base, northwest of Las Vegas. They said the Marines had been conducting unit-level training and were returning home to Marine Corps Air Station Miramar in San Diego.