Bonnie Mitsui was a lover of the land who nearly 30 years ago became one of the first Sonoma County ranch owners to deed their development rights to a conservancy, and who long envisioned a hilltop hiking trail from east of Petaluma to Jack London State Park in Sonoma Valley.

Mitsui died May 11 in her native Cincinnati, Ohio, where the former killer of house plants became so adept at gardening that she operated a thriving organic farm currently harvesting more than 100,000 pounds of produce a year.

Mitsui, who never lived full-time on her property on Sonoma Mountain but often took her two young children there from the family home in Mill Valley, was 69. Her death came from complications of lung cancer diagnosed in 2007.

"She's had her impacts on Sonoma County, in many ways," said longtime friend and ally Bill Kortum, the Petaluma environmentalist and former Sonoma County supervisor.

Kortum said that going back to the 1970s, when Mitsui and her family settled in Marin County, she was a generous contributor and advocate for the League of Conservation Voters and many other environmental initiatives.

"I believe she had the first land conservation easement in the entire county. Now they're all over the place," Kortum said.

Mitsui purchased the 630-acre hillside ranch east of Petaluma in 1975.

"She bought it to have a place to raise her kids out of the city, and to ride horses," said Jeff Wilcox, the property's managing ecologist.

In 1984, Mitsui assured the Sonoma Mountain ranch land would never be developed by granting a conservation easement to the Nature Conservancy.

She returned to rural Ohio in 1993, and in 2003 made a a stunning offer she hoped might lead to resolution of a stubborn legal battle over the long-attempted conversion of Sonoma Mountain's Lafferty Ranch to a public park.

Mitsui said that if the parties would settle the issue and open the park, she would donate a 1.45-mile easement across her property for use as a trail — with magnificent, high-up views — to link the Petaluma park to the Glen Ellen area's Jack London State Park.

To this point, the legal obstacles have not been overcome. Kortum said he and other proponents of a Sonoma Mountain park and a scenic ridge trail to Sonoma Valley have not given up.

Mitsui never formalized the offer of a trail easement in writing. Last year, she created the Sonoma Mountain Ranch Preservation Foundation to manage the property, return it to its natural state and make it available to students and researchers.

The foundation's attorney, Robert Edmiston, said that were a public park to be opened at Lafferty Ranch and a request made for the trail easement Mitsui offered, that request would be considered by the foundation's board of directors.

At this point, said Wilcox, who manages the ranch for the foundation, no one lives on the property and few people come onto it. Petaluma brothers Jim and Doug Dolcini are allowed to graze cattle there, in part to control non-native grasses.

Wilcox said Mitsui was a remarkable person — "pragmatic, frugal ... she saw situations quickly, she grasped them quickly.

"And she was fearless in trying new ways, absolutely fearless."

Though she knew nothing about farming, the woman who was born Mary Elizabeth Crudgington left California in 1993 to return home to Ohio and learn organic, low-tech agriculture on Turner Farm, which she'd inherited from her grandmother.

Neighbors and passersby often waved to her as she drove a horse-drawn carriage. Mitsui continued to help work the farm after she suffered a serious stroke in 1999 and was diagnosed with lung cancer eight years later.

She is survived by her children, Natsu Alexandra Mitsui of Tokyo and Takeru Mitsui of Kaaawa, Hawaii, and one grandson.

— Chris Smith