San Francisco publishing heiress Nan Tucker McEvoy raised locals? eyebrows nearly 20 years ago when she transformed an old dairy outside Petaluma into a lush estate that produces Tuscan-style olive oil.

On Wednesday, McEvoy Ranch struck another blow against convention, unveiling a 140-foot windmill that will supply all of the estate?s power.

?This will bring the ranch as close to carbon neutrality as we can,? said McEvoy?s son, Nion McEvoy.

It?s the largest windmill in Marin County and the first private wind project of its size to power a California agriculture operation, the McEvoys said.

The three-bladed windmill sits on a 680-foot knoll on the west side of the ranch, where westerly winds sweep in at an average 10 miles per hour, according to Dave Williard, a green energy consultant who managed the project.

Its white tower rises nearly 100 feet, and the blades reach another 40 feet.

The mill?s turbine will generate 225 kilowatts of electricity, enough to run McEvoy Ranch?s olive processing plant and other operations, he said.

The windmill didn?t come without opposition. Neighbors objected to its original size and location, saying it would be too tall, too noisy and too dangerous for birds.

McEvoy Ranch downsized the windmill from 210 feet and moved it to different location. Planners worked with bird experts to minimize the impact on wildlife, Williard said.

Marin County leaders approved it in 2007.

?It?s been a little controversial in this part of Marin,? Nion McEvoy said Wednesday. But even critics should appreciate its energy savings, he said.

The ranch?s greenhouse gas emissions should fall by more than 100 tons a year, according to the McEvoys.

They wouldn?t disclose the project?s cost.

Nan McEvoy is the granddaughter of San Francisco Chronicle founder Michael de Young, and she led the newspaper?s board from 1981 to 1995. De Young?s descendants sold the newspaper in 1999 to the Hearst Corp. for $660 million.

Nion McEvoy is chairman of Chronicle Books, an independent publisher in San Francisco.

Nan McEvoy bought the 550-acre ranch three miles southwest of Petaluma in 1991. She planted 18,000 Italian olive trees on 80 acres and imported Italian equipment for her olive processing mill.

The estate produces certified organic extra virgin olive oil, honey, jams, soaps and other products. McEvoy Ranch olive oil sells for more than $20 per 375-milliliter bottle in stores including Whole Foods Market and at the McEvoy Ranch retail shop in San Francisco?s Ferry Building.