SAN JOSE — When Walter Cottle Lester was a boy growing up on his family farm in the 1930s, thousands of acres of prune, apricot and cherry orchards bloomed across Santa Clara Valley. As time marched on, however, developers turned the pastoral “Valley of Heart’s Delight” into subdivisions, freeways and electronics companies.

Nearly everything around Lester’s family farm has changed. But Lester, and his farm, have not.

On Friday, construction crews began work on a project to turn Lester’s 287-acre property, surrounded on all sides by development, into a new public park to showcase the agricultural heritage of Santa Clara County, provide new recreational opportunities for Silicon Valley families and make sure crops will continue to be grown on the land for years to come.

“It’s part of history here. It goes way back to my grandfather’s time,” said Lester, 88. “I was born here. I’ve spent my entire life here. It would be nice for kids in future generations to know what it was like before it all changed.”

Lester, who never married and has no children, donated the property, now called Martial Cottle Park, after his grandfather, to the Santa Clara County Parks and Recreation Department and the California state parks department. Through the years, he and his late sister, Edith Lester, had single-handedly held back the forces of Silicon Valley’s relentless urban sprawl, turning down countless offers that could have earned them hundreds of millions of dollars for the vast open space in the middle of America’s 10th largest city.

“It was very upsetting to see the farmland disappear,” he said Friday. “I wasn’t interested in selling. I wanted to maintain what we had the way it was.”

The property is in South San Jose, bounded by Chynoweth Avenue, Snell Avenue, Branham Lane and Highway 85. A few blocks away are a spate of fast-food restaurants and cul-de-sacs. But Lester’s property features huge pastures, centuries-old oak trees and hand-painted signs along the edges advertising “vine ripe tomatoes,” “fresh strawberries” and “fresh picked corn” for sale at a farm stand on the property.

“He dug in and held his ground,” said Alicia Flynn, capital projects manager for Santa Clara County parks. “This would have been a shopping mall. It is an incredible gift to the public and an incredible legacy.”

Construction crews will build a 4-mile trail around the perimeter of the property. Half of the trail is scheduled to be opened by December.

Workers also will build a 3,500-square-foot visitor’s center, parking, family picnic areas and a “discovery farm” with exhibits for children on the property, which is the size of roughly 230 football fields. Those features, and the property itself, are set to open to the public by December 2014. Total construction cost: $26 million, paid by the county’s voter-approved parks charter fund.

As it has been since the 1860s, the bulk of the property will remain in farming, with the county hiring a manager to oversee farmers who will lease the land in future years. Portions also will be devoted to a community garden, areas for children in 4-H to raise animals, agricultural research for the University of California and other related projects.

Lester, a private man who doesn’t like public accolades or even having his picture taken, will continue to live in the white 1870s-era farmhouse on the property, surrounded by 30 acres that will stay in private ownership until he dies. That landscape then will become part of the larger park.

The land is now rich with the coming bounty of a fall harvest. Rows of sweet corn grow 7 feet tall. Pumpkin vines stretch across neat furrows. Cherry trees, old tractors, plows, irrigation pipes and horses encircle Lester’s house.

“This has been his world for his whole life,” said David Giordano, of San Jose, who manages farm operations for Lester.

“He took me upstairs in his house once and said, ‘See that bed? I was born in that bed. And my mother was born in that bed.’ His family hasn’t changed over all these years.”

The property has a rich history that dates back to before the Gold Rush.

It was originally part of the 9,600-acre Rancho Santa Teresa. The rancho was a 9,600-acre Mexican land grant given by the Mexican governor of Alta California in 1834 to Jose Joaquin Bernal, a Spanish soldier and member of the 1776 De Anza Expedition that first settled San Francisco. After California became a state in 1850, the land was purchased in 1864 by Edward Cottle, who later donated 350 acres to his son, Martial Cottle.

Martial Cottle raised cattle and grain and other crops, and left the property to his daughter, Ethel Cottle Lester. After she died in 1977, the ranch went to her children Edith and Walter Lester. Edith Lester died in 1999, leaving Walter Cottle Lester as the only owner.

After Edith died, Walter faced millions of dollars in estate taxes. His attorney, now-county Supervisor Dave Cortese, contacted former state parks director Rusty Areias, who helped secure $5 million in state parks bond money to pay the taxes so the land could be donated free and clear to the county in 2004. Under the deal, although the state owns half the property, county rangers will patrol and maintain the land.

“A lot of kids don’t understand where their food comes from. It’s important for their health and it’s just good for their historical knowledge to have a place like this,” said county park ranger Carolyn Tucker. “As soon as you walk in here you are completely removed from the surrounding communities. It’s just like going back in time.”

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/paulrogerssjmn.