A fast-moving wildfire ripped through rolling hills and ranchland in rural northern California on Tuesday, after destroying 30homes overnight and prompting more than 500 area residents toevacuate, fire officials said.

The so-called Clover Fire, which broke out on Monday afternoon,has already scorched some 7,400 acres near the rural community ofHappy Valley in Shasta County, some 200 miles north of SanFrancisco, according to the California Department of Forestry andFire Protection.

Temperatures above 100 degrees have made for tough conditions onthe fire lines, and four people, three of them firefighters, havebeen treated for smoke inhalation, CalFire spokeswoman Teresa Reasaid.

In addition to the 30 homes considered total losses, at leastanother 50 outbuildings had been damaged or destroyed by the blaze,named after its place of origin, Cloverdale Road near Happy Valley.Officials had earlier said 80 structures were destroyed and 30 moredamaged.

Some 300 homes remained under threat, prompting the evacuationsand a number of road closures in the area. The fire was 40 percentcontained as of Tuesday afternoon.

CalFire spokesman Mike Witesman said the blaze was movingquickly over hilly, rocky terrain and consuming dense vegetation,including grass, shrubs, oak and pine trees.

“Because of the very dry weather we've had, the conditions arevery volatile,” he said, adding that on Monday the flames hadspread at a rate of about 500 acres per hour.

More than 1,120 firefighters were on the ground on Tuesday,digging containment lines around the blaze, while air tankersdropped water and fire retardant on the flames.

SPOT FIRES ERUPT

Crews have shoveled and bulldozed lines around the entireperimeter of the conflagration, one of dozens of wildfires thathave spread across the drought-parched U.S. West in recent months,straining national firefighting resources.

Because of the dense vegetation and dry landscape, the fire cangain momentum and send out embers that create smaller fires outsideof containment lines, and it was not clear if the lines will checkits spread, Witesman said.

“We don't consider it contained until we're pretty sure thatit's going to hold,” Witesman said. “Yesterday, spot fires were asignificant problem.”

He said the fire had also created its own winds, which allow itto spread more quickly, adding to already windy weather in thearea.

The Clover fire was burning about 200 miles north of a mountainblaze east of San Francisco that forced the evacuation of about 100homes at the edge of the town of Clayton on Sunday.

The so-called Morgan Fire, which has blackened some 3,200 acresin and around Mt. Diablo State Park, was 45 percent contained as ofTuesday morning, according to a CalFire website, and coolertemperatures were helping crews make progress.

The state park, about 20 miles inland from the eastern edge ofSan Francisco Bay, has been closed to visitors.

Meanwhile crews were still at work on the massive Rim Fire,which has been burning in and around Yosemite National Park sincemid-August.

That fire, believed to have been sparked by a hunter's campfire,has blackened nearly 400 square miles of timber and dry brush,making it the third-largest California wildfire on record.