A storm that parked itself over Southern California for days, unleashing historic downpours that caused hundreds of landslides, is expected to move out of the region after one final drenching. But authorities say it leaves behind the threat of dangerous mudslides because the soaked soil cannot hold any more water. At least seven people have died, many from falling trees, since the storm first struck Northern California last weekend and then plowed south. Forecasts call for only one heavy downpour on Wednesday followed by a drying-out period and a sunny weekend.