The property also includes a summer mansion and related buildings. The Hawthorns, as the property has been known, was the home of the Woods family. Frederick N. Woods III, who died in April 2008 at age 93, willed it to the open space district upon his death.
The property will become part of the Windy Hill Open Space Preserve, district spokeswoman Leigh Ann Gessner told the Almanac.
The property is valued at $11 million, comes with a $2 million endowment for maintenance and stewardship, and is the largest gift of open space from a private family in the district's 39 years, Ms. Gessner said. It is also the first gift that included an endowment, she said.
Town Councilman Steve Toben called the gift "extraordinary to all who cherish open space." He said it is "remarkable to contemplate that these 79 acres will remain undeveloped in perpetuity, held in public trust for the benefit of natural communities and anyone who seeks refuge from the stresses of modern life."
Added former mayor Gary Neilsen: "Although this gift appears to be a direct benefit to Portola Valley residents, we in town will want to share this open space, and gladly so, with all of our neighbors in the region when it becomes accessible."
The property will remain closed to the public at least until the district goes through the public planning process, including public hearings and an analysis of access for the public and the opportunities for environmental conservation and historic preservation.
How long might all that take? "It's hard to say. There are lots of projects in the hopper," Ms. Gessner said. "It's not really something that we planned for."
Immediate steps include setting up patrols by district rangers, reducing wildfire risks and disking the ground along the perimeter, Ms. Gessner said.
As for animals of importance to the environmentally minded, Los Trancos Creek defines the eastern border of the property and is thought to be home to steelhead trout. Other native species of threatened or endangered status include the California red-legged frog and Bell's vireo, the peregrine falcon and the willow flycatcher, all birds.
Botanical species include the remains of an olive orchard, oaks, bay laurels and buckeyes as well as willow, alder and cottonwood trees near the creek, said Ms. Gessner, who has visited the property.
"The cottonwood trees were releasing their floaty white stuff into the air. It was kind of surreal," she said. "There is a really wonderful view from the top."
"It is one of last remaining islands of open space in the residential area of Portola Valley," Ms. Gessner said, noting that it had the potential for 22 residences.
The Peninsula Open Space Trust (POST), a private nonprofit land trust, arranged a conservation easement in 2005, which had the effect of curtailing some development rights.
The buildings, including the mansion, may be historic and date from the late 19th century, Ms. Gessner said, adding that the district will probably need a management partner with expertise in such matters.
Visit tinyurl.com/PV-194 to see a PDF document with a map of the area being acquired.