Firefighters guarded rural homes, ranches and orchards Wednesday as a wind-driven wildfire grew to more than 25 square miles on a march through rugged land between small Southern California communities Wednesday.

The fire was stoked by hot and dry Santa Ana winds but firefighters said the windspeeds were lower than on the first day of the blaze.

Containment of the fire, about 40 miles northwest of downtown Los Angeles, also increased to 40 percent, but it was not expected to be fully surrounded until Saturday. Firefighters cut and burned away brush along a canyon road to try to corral part of the fire's western flank.

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Fire officials said the blaze began Tuesday in the area of an agricultural mulch pile, but the cause remained under investigation. The Sheriff's Department earlier said it was apparently caused by spontaneous combustion in manure.

Winds and fuels such as grasses and light brush made the fire dangerous, said incident commander Robert Lewin.

"Our firefighters need to be on guard, make sure they're out of harm's way when they're engaged in this fire, and so do the citizens," he said.

About 1,000 homes were considered threatened as the fire burned east and west just north of Moorpark, a city of 37,000. The 15,000-student Moorpark College was closed because of its proximity to the fire.

Reverse 911 calls recommending evacuations were made to 2,200 phones in unincorporated areas, but officials couldn't say how many people actually left.

One of those calls went to the home of school bus driver Maria Kadowaki in Somis, west of Moorpark.

"I wasn't too frightened but my husband freaked out," she said. "He ran outside and started watering the garage in the dark."

They chose not to leave their home, and Wednesday afternoon she and another driver were out checking which roads would be open or closed when they took children home after school.

Two outbuildings were destroyed but no homes had been damaged.

The fire was also threatening agricultural properties, a major concern in a county where the industry was valued at $1.6 billion last year.

"There are very, very valuable avocado groves and other agricultural values out there, and we are doing everything we can to protect those," Lewin said.

Helicopters dumped water on flames moving toward orchards and ground crews put out burning shrubbery at the edges of groves. County fire Capt. Ron Oatman said the fire likely had burned some peripheral trees but agricultural damage had not been confirmed.

Firefighters were also concerned about five major electrical transmission lines, a 36-inch natural gas pipeline and oil production fields within the fire perimeter, he said.

Firefighting costs surpassed $1 million as nearly 900 firefighters, 18 air tankers and 12 helicopters worked the blaze. Four injuries were reported but all were minor.

The blaze was the largest of several fires that erupted in Southern California on Tuesday as the Santa Anas blew in from the northeast, pushing back the normal flow of cool and moist ocean air.

Forecasters said weak Santa Anas would continue until Friday.

During a calm period early Wednesday, Marieke Lexmond stood with her dog Flynn and recalled the scary rush of fire and smoke past her rented Balcom Canyon home.

"It was a serious wind and the fire came out of the hills and it was burned out in 30 minutes," she said.

Lexmond and neighbors gathered horses into a corral in preparation for evacuation.

"We have the cars packed and we are ready to go. When it comes this close, you don't care. You take your passport and papers and animals and go," Lexmond said.

An animal evacuation center at the county fairgrounds had 136 horses, three donkeys, three pigs, two goats and a lamb.

Elsewhere in California, a fire that burned close to homes in the Riverside County city of Norco was just a black scar on the land by Wednesday morning, with no smoke or flames apparent.

Meanwhile, the hot, dry and windy weather increased fire activity northeast of Los Angeles in the San Gabriel Mountains, where remnants of a month-old, 251-square-mile wildfire are still smoldering. A 20-acre spot fire in was held in check by air drops of retardant, the U.S. Forest Service said.

Completion of containment lines around the giant blaze was expected Thursday, the service said. The fire destroyed 89 homes and caused two firefighter deaths in August.

A 300-acre wildfire burning in a heavily wooded area of Sonoma County near Geyserville was 90 percent surrounded, with full containment expected Thursday.

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More on this story from the Ventura County Star