Much of Southern California was pounded Wednesday by a powerful storm that dumped as much as a foot of rain in the mountains of Los Angeles County. Falling an inch an hour in some areas, the downpour caused several minor mudslides, collapsed roofs, and flooded roads and underground parking garages in the first significant rainfall the region has seen since April.

Flash-flood warnings were issued for parts of four counties as rescue crews kept a close watch on the denuded hills that were ravaged by last year's deadly wildfires. The blazes killed 20 people, destroyed 3,570 homes and scorched over 750,000 acres, leaving the burned-out areas susceptible to mudslides. Thirteen people -- including eight children -- were killed when a flash flood swept through a mountain campground on Christmas Day.

On Wednesday, crews found the body of a 19-year-old security guard who slipped into a gully in northern Los Angeles County.

Another weaker storm is expected to hit the region this weekend, and snow is expected in the higher elevations.

The rain was welcomed by state fire officials, who had been predicting that severe drought conditions would lead to a devastating fire season. Recent rainfall prompted the easing of fire restrictions. Thousands of acres of national forests, which had been closed since September because of extreme fire danger, were reopened Wednesday.

The powerful storm attracted wall-to-wall coverage by local television and radio stations as residents bundled in winter coats and armed with umbrellas slogged their way through flooded streets.

The morning commute was reduced to a crawl as drivers struggled with the wet and oil-slicked roads. Accidents doubled on Los Angeles County freeways when the rain started to fall.

"It's simply driver error," said California Highway Patrol Officer Armando Clemente. "People are not accustomed to the rain here. They tailgate, they don't slow down, and they make unsafe lane changes."

Residents of a mobile home park in Newhall, in northern Los Angeles County, were temporarily stranded in their units after mud and debris four feet deep blocked the only access road to the park. Several roofs collapsed. Commuter train service in San Bernardino and Riverside counties was brought to a standstill after heavy flooding submerged train tracks.

Sporadic power interruptions, ranging from flickering lights to power outages lasting for several hours, were reported across the region. About 300,000 electricity customers were affected statewide.

Jef Dillon placed sandbags at the door of a storage building in Devore as Southern California braced for flash floods.