SACRAMENTO (REUTERS) - One person died and thousands of people were stranded after thunderstorms raged through Southern California mountain communities on Sunday, unleashing mudslides and floods, officials said.

San Bernardino County Fire Department Captain Kyle Hauducoeur said it would take up to three days for workers using bulldozers and other heavy equipment to clear roads around Forest Falls enough for residents and traffic to move freely.

Mr Hauducoeur said one person was discovered dead inside a vehicle that had been washed off a Mount Baldy road during the heavy rains roughly 80 kms northeast of Los Angeles.

Thousands of others were stranded by the quick-moving waters in the towns of Oak Glen and Forest Falls, though no further injuries were reported as of Monday morning.

Amongst those stranded were some 500 children and chaperones who had arrived at a Forest Falls campground earlier on Sunday but could not leave after roads were covered with mud, rocks, trees and other debris. "Our priority is using heavy equipment ... to open access to that camp," Mr Hauducoeur said.

Roads across the area were completely washed out, according to pictures posted online by the San Bernardino County Fire Department.

County emergency responders rescued one woman before a mudslide destroyed her Mount Baldy home and damaged four other nearby buildings, Mr Hauducoeur said.

The National Weather Service said flash flood warnings were in effect through the earlier hours of Monday morning in parts of San Bernardino County.