Another 28 injuries have been reported in Santa Barbara County following the deluge that overwhelmed an area scorched by wildfires last month.
More than 100 homes were destroyed, and another 300 have been damaged.
More than 50 people have been rescued already but many places were still inaccessible. Several roads were closed, including the major Highway 101 which authorities say will not be reopened until Monday.
The first rain in months caused mudslides when it hit ground that had been burned by December's huge wildfires.
After a wildfire, burned vegetation and charred soil create a water repellent layer which blocks water absorption. Together with the loss of vegetation, this leads to an increased risk of mudslides and floods.