Fire crews set backfires to halt flames from reaching a remote community in northern Ventura County threatened by one of the largest and longest-burning wildfires in state history.

Authorities issued a voluntary evacuation Monday evening for about 500 people in Lockwood Valley when flames jumped over a fire line and quickly reached a peak about 1 1/2 miles from the community.

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Firefighters took advantage of calm winds and set a backfire toward the fire line, and 45 engines were deployed to protect ranches scattered around the area, fire spokesman Dan Bastion said.

Tuesday's forecast called for winds moving about 8 mph, which will allow firefighters to escalate attacks on the fire, Bastion said.

The blaze, ignited by someone burning debris, has burned 218 square miles, or 139,720 acres, in the area 75 miles north of Los Angeles since it began on Labor Day. It was 41 percent contained.

The weather was expected to remain mild through the week, with high temperatures reaching the low 80s.

Gov. Arnold Schwarzenegger has declared a state of emergency for Ventura County. The move clears the way for government assistance with costs related to the fire.

More than 3,500 firefighters were trying to encircle the blaze, which has cost $43.6 million to fight.

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