SAN JOSE — Walter Cottle Lester, who passed up a staggering fortune to donate his family’s vast farm land to ensure Silicon Valley would forever maintain a piece of its agricultural roots, died of natural causes Friday afternoon at age 88.

Heartbreakingly, he passed away the day before the opening of the public trail he fought so hard for — one that helped him preserve his family’s 237-acre ranch in South San Jose. Santa Clara County Board of Supervisors President Mike Wasserman turned Saturday morning’s event into a “Walk for Walter,” who had been confined to his house under nurse’s care for several months.

Lester gave up more than $500 million, turning away repeated bids from developers to build on his pristine land that his family kept for three generations since the 1860s and is considered the biggest farm left in San Jose.

“People ask: Why didn’t Walter sell and go buy an island? Well, his world was right here,” said David Giordano, who managed the farming operation for Lester the last two decades. “His duty in life, as he perceived it, was to preserve the ranch in its entirety.”

The last surviving member of the Cottle family, for which Cottle Road is named, Lester was reclusive, never married and had no children.

Over the last few years, Lester donated his land to Santa Clara County and the state of California in exchange for their agreement to turn the area into a $26 million park that cannot be developed and will include plenty of land for farming.

The donation helped Lester avoid the vast majority of a more than $100 million estate tax bill associated with the death of his deaf and blind sister 15 years ago, since she co-owned the land. The bill would have forced Lester to sell a big chunk of his land — a painful and unimaginable fate.

Lester’s passion for preserving the estate reaches back to his ancestors who were on their way to Oregon in covered wagons before they ultimately settled in San Jose 150 years ago. His grandfather, Martial Cottle, gave the land to his daughter, Ethel Cottle Lester, who passed it on to her children, Walter Cottle Lester and his late sister, Edith.

The South Bay region was once known as the Valley of Heart’s Delight for its rich orchards, but as technology companies and others took over in the mid-20th century, lands like the Cottle spread were steadily sold and systematically sprouted homes, offices and shopping malls. The one big holdout was Lester.

To this day, cherries, plums, apricots, peaches and grains are grown on the land and sold from a fruit stand between Highway 85 and Branham Lane. Lester had lived in a 140-year-old farmhouse there and used to proudly drive his pickup truck around the property also rimmed by Snell and Chynoweth avenues.

Though he was distrustful of government, Lester dedicated the latter part of his life to crafting an ironclad deal with the county and state to ensure the land would remain as open space after his death — the end of his family’s blood line. After help from local officials and funding from a state parks bond, he finally accomplished that goal and crews broke ground on the park in August.

“He was just a crusty old farmer who had a dream, and he stuck with it. He was stubborn and crotchety and a loner in many ways. He knew what he wanted,” said Susanne Wilson, a former county supervisor who worked with Lester on the preservation effort. “He wasn’t about to relinquish one bit of that land. He was here first and by golly he had rights.”

In addition to the new 4-mile trail that rings the property, in the coming years, the new Martial Cottle Park will also include picnic areas, a visitors’ center and land that can be leased for farming. Although Lester didn’t get to see the full vision come to fruition, Giordano and his cousin, Frank, who also worked with Lester for decades, said he was content with the plans he had laid out.

“He drew his first and last breaths there, and you can’t say that about a lot of people,” Frank Giordano said. “We’re going to certainly miss him.”

County Supervisor Dave Cortese, who was Lester’s lawyer in the late 1990s before getting into politics and also grew up on a nearby ranch, said Lester repeatedly told him he wanted future generations to be able to have a similar place to visit in San Jose.

“You’re almost transcending space and time when you walk into the place,” Cortese said. “It’s going to be that way forever now.”

Contact Mike Rosenberg at 408-920-5705. Follow him at twitter.com/RosenbergMerc.