Firefighters worked to keep flames from reaching more homes after a lightning-sparked wildfire advanced Thursday in the Sierra Nevada foothills of California.

The wildfire in Butte County destroyed at least 50 homes earlier in the week, mostly in Concow, and has sent as many as 10,000 residents fleeing. It continued burning through brush and trees, but no other homes were reported lost overnight, officials said Thursday.

"Things were looking good overnight," said Anne McLean, a spokeswoman for the California Department of Forestry and Fire Protection. "So far, so good."

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

Firefighters also dealt with hot, dry weather that was expected to continue through the weekend. At least six firefighters were treated for heat exhaustion Wednesday, said Mike Mohler, a state fire department spokesman.

"We have low humidity, high temps and then the wind, so the conditions are still red flag," Mohler said. "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 part of a complex of about 40 lightning-sparked wildfires that over the past two weeks have charred 49,000 acres — or more than 76 square miles — in and around Butte County. By Thursday, there were about 15 active fires.

"You almost feel like somebody is out to get you," said Nancy Henphill, 61, of Concow. She and her husband were forced to leave their home twice in just over two weeks.

Across the state, fire crews have strained to cover hundreds of wildfires that have burned nearly 1,100 square miles and destroyed nearly 100 homes since a lightning storm ignited most of them more than two weeks ago. Some 1,460 fires had been contained, but more than 320 were still active Thursday, authorities said.

Gov. Arnold Schwarzenegger's office said Thursday that the governor sent a letter to President Bush asking to send more firefighters to help build fire lines and train National Guard troops deployed to assist firefighting efforts.

"California is in the midst of battling unprecedented wildfires that have stretched our state's firefighting resources to their limit and placed thousands of Californians in immediate danger," Schwarzenegger said in the letter.

East of Bakersfield, a fire covering more than 50 square miles was 28 percent contained and was not threatening any homes, fire spokesman Dwight Robanske said.

On the state's central coast, authorities late Wednesday issued new mandatory evacuation orders for about 50 homes along a rugged road leading to the historic Tassajara Zen Mountain Center in the mountains east of the Big Sur community.

Monks at the Zen center had spent weeks preparing to fight the blaze as it approached through the Ventana Wilderness, but all but five residents had decided to flee Wednesday night, according to the center's Web site.

Many other Big Sur residents returned 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.

A separate 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 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 girls, 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."

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By DON THOMPSON, Associated Press Writer

Copyright © 2008 The Associated Press. All rights reserved.