A wildfire in Butte County, California, has forced the evacuation of as many as 10,000 residents.

The fire is one of about 40 sparked by lightning that have charred 49,000 acres — or more than 76 square miles — in the past two weeks.

Firefighters currently are making their stand along the Feather River on the banks opposite of the city of Paradise, which is at risk if the winds shift. The fire threatens nearly 4,000 homes in Paradise, where a separate wildfire destroyed 74 homes last month.

A state fire department spokesman says at least six firefighters were treated for heat exhaustion yesterday — the result of hot, dry weather that's expected to continue through the weekend.Governor Arnold Schwarzenegger has asked President Bush to send more firefighters to help.

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By early Thursday, the lightning-sparked wildfire had destroyed at least 50 homes, mostly in the rural community of Concow, about 90 miles north of Sacramento.

"We have low humidity, high temps and then the wind, so the conditions are still red flag," meaning the most extreme fire danger, said Mike Mohler, a spokesman for the California Department of Forestry and Fire Protection. "If the weather cooperates, we have a good chance. But it all depends on what Mother Nature gives us the next few days."

The blaze is one of about 40 lightning-sparked wildfires that have charred 49,000 acres in this northern California region during the past two weeks.

For Clay and Nancy Henphill, running from raging wildfires is becoming routine. They were forced to evacuate their home for the second time in just over two weeks.

The Henphills awoke to blaring sirens around 1 a.m. Tuesday and were told to leave immediately. Only a week earlier, they had returned to their home in Concow after spending a week at a shelter.

"You almost feel like somebody is out to get you," Nancy Henphill, 61, said Wednesday.

Firefighters faced a sudden drop in humidity and triple-digit temperatures amid a heat wave that was expected to last until the weekend. At least six firefighters were treated for heat exhaustion Wednesday, Mohler said.

In Concow, small flames flickered and smoke rose from charred trees and homes. Firefighters were able to save most of the houses, often stopping flames at the doorsteps.

Fire crews across California have been straining to cover hundreds of wildfires that have burned more than 1,000 square miles and destroyed nearly 100 homes since a lightning storm ignited most of them more than two weeks ago. Some 1,450 fires had been contained Wednesday, but more than 320 still were active, authorities said.

On the state's Central Coast, firefighters pushed back a blaze threatening Big Sur — enough to allow hundreds of people to return to their homes Tuesday and Wednesday. At least 27 homes and 31 other structures have been destroyed in Big Sur. The fire has burned more than 140 square miles.

Fire officials said the blaze is still searing the mountains east of the Big Sur community and had crept within a mile-and-a-half of a historic Zen monastery.

Monks at the Tassajara Zen Mountain Center had spent weeks preparing to fight the blaze, but they decided to flee Wednesday night, according to the center's Web site.

A fire burning in the Santa Ynez Mountains above the Santa Barbara County coast was more than half contained Wednesday. More than 1,100 firefighters, nine helicopters and five air tankers were attacking the blaze, which had blackened more than 15 square miles of land northwest of Los Angeles.

Some people who had been forced to flee days ago were settling back in.

Wieke Meulenkamp, a mother of two young daughters, had gathered her family, valuables and two dogs and fled the flames, staying with friends for three days. They returned on Sunday to their home in the mountaintop community of Painted Cave near Santa Barbara.

"It looks pretty good now," she said. "But you're never out of danger up here."