A potent winter storm that hammered the West Coast over the weekend triggered mudslides in Southern California in areas scorched by wildfires, trapping drivers and shutting down a major thoroughfare. On Sunday, crews towed away cars and worked to clear lanes of mud and debris along the Pacific Coast Highway that had been closed in both directions Saturday night. A portion of the road in Malibu will not reopen until at least Monday, the California Department of Transportation said. Motorists became trapped in their cars when torrents of mud cascaded down hillsides along the scenic highway.