Firefighters struggled Thursday to control a blaze along a 15-mile ridgeline in a hilly area of suburban homes that consumed one house and five outbuildings and forced the evacuation of at least 500 people. One firefighter was injured.

In addition to the 17,000-acre blaze north of the city, as many as eight smaller fires were burning in Los Angeles County and to the east in Riverside and San Bernardino counties, closing schools and prompting air pollution officials to urge residents to stay indoors.

The fires are being fed by dense undergrowth, the result of exceptionally heavy rain last winter and then an unusually long dry season, officials said.

"I always say, the way you spell fire is F-U-E-L," said Bill Patzert, climatologist at NASA's Jet Propulsion Laboratory. "There has been a lot of fuel building here, with the big drought and the big rains."

Fanned by the first hot Santa Ana winds of the fall wildfire season, the blazes tinged the city air with the scent of smoke.

The largest blaze, near affluent Simi Valley, on the border of Los Angeles and Ventura counties, began Wednesday afternoon as a small brush fire that consumed 300 acres in about an hour. But with winds gusting to 40 mph, it had scorched 7,000 acres before dawn Thursday. Firefighters went door to door in the nearby canyon communities, rousing sleeping residents.

Late Thursday, the fire had grown to 17,000 acres and was still only 5 percent contained. One firefighter was injured when a rock fell on his back, officials said. The firefighter was treated at a hospital and released.

A plume of smoke was visible across the Los Angeles basin. Schools were closed and traffic was rerouted in the affected areas. High schools and community centers were quickly transformed into evacuation centers.

Three thousand firefighters from city, county, state and federal agencies worked to keep the blaze from jumping busy Freeway 101 or veering into densely populated Simi Valley. They were aided by lighter winds, though temperatures still climbed into the nineties with very low humidity.

In the past, fires in the area have burned south through the Santa Monica Mountains and into Malibu, home to gated estates concealed in canyons near the ocean.

In Riverside County, a fire that started on a commercial chicken ranch killed hundreds of chickens and spread to 1,300 acres. The threat to homes there was minimal, said officials who expected the fire to be contained by Thursday night.

David Hillman, chief of California's Department of Forestry and Fire Protection, said he worried about fire with the first hint of warm, windy air on Wednesday.

"When I walked outside yesterday afternoon, I dare say I had the same feeling every firefighter in Southern California had," he said. "I felt the wind in my face and I wondered, later on that day, where would I be."

The weather forecast calls for diminished winds and lower temperatures over the next two days. Patzert, the climatologist, said there was no predicting whether the winds would spring back up.

"If the Santa Anas keep coming like the hurricanes have, it could be bad," he said.

A helicopter makes a water drop on a wind-whipped wildfire in southern Ventura County, north of Los Angeles.