Sonoma County supervisors hailed a landmark conservation deal Tuesday as they unanimously approved $4 million in open space dollars to help with the $24.5 million purchase of Preservation Ranch in the county's northwest corner.

"It's a great day for residents of the county and the entire North Coast," said Supervisor Efren Carrillo, who represents west county, including the rugged swath of coastal forest where the 19,650-acre property sits.

The funding clears the way for the largest conservation deal by acreage in county history, set to close May 31. It also defuses a prolonged battle over a plan to clear nearly 1,800 acres of forest for winegrapes.

The proposal, backed by CalPERS, the giant state workers pension fund, drew national media attention and provoked widespread opposition from environmentalists, local tribes and even some winemakers.

By comparison, the purchase deal that derails the vineyard project reached late last year between CalPERS and public and private conservation officials, enjoyed relatively little fanfare Tuesday. The smaller crowd meant good news, supporters said. The fight is over, they said.

"If a couple of years ago you'd told me that the Board of Supervisors would be looking at Preservation Ranch and the chambers would be half empty, it would have been unbelievable," said Ralph Benson, executive director of Sonoma Land Trust, the private nonprofit that is a partner in the deal.

For Carrillo, who was credited with helping to advance the purchase, the political risks inherent in a vote on the vineyard proposal were especially high. The 32-year-old supervisor, who is considering a run for a seat in the state legislature, expressed some relief Tuesday.

"I can imagine the packed room if we had had an alternative proposal before this board," he said. "I won't go there."

Once home to the Kashia Pomo, the hilly ranch was heavily logged in the 1950s and '60s. It includes 20 miles of streams inhabited by coho salmon and steelhead trout, while mountain lions, bobcats and deer roam the land.

CalPERS, the $263 billion state workers pension fund, has controlled Preservation Ranch for nearly a decade. For most of that time, the ownership was through a Napa-based vineyard development firm that bought the property in 2004 for $28.5 million.

The Board of Supervisors' decision approved use of $4 million from the county's Agricultural Preservation and Open Space District for the purchase. In exchange, the county gets a conservation easement that bans forest conversions, erases development potential over 154 parcels and restricts use of the property to sustainable forestry, grazing and public recreation.

The Conservation Fund, a private Virginia-based group, will own and maintain the property, managing it for timber and carbon credits and keeping it on the tax rolls. It is contributing $6 million and has secured $3.5 million in financing.

The state Coastal Conservancy, a public agency, last month approved $10 million toward the deal.

Sonoma Land Trust, the Santa Rosa-based nonprofit group, is set to contribute $1 million through a grant from the Gordon and Betty Moore Foundation.

The public funding comes with requirements to explore and develop opportunities for public recreation.

Tuesday's hearing featured some discussion of an access issue that could preclude general public visits to the ranch, at least in the short-term.

Kelly Road, the main artery through the area, is privately owned. Dave and Bunny Lewers, the road owners, say their agreement with the county for public access to a nearby county park wouldn't cover entrance to Preservation Ranch.

They offered to sell the county the two miles of road in question. Later, in an interview, they said they had not set a sale price. The county would be limited to providing only fair market value. It has not ordered an appraisal on the road segment.

County and conservation officials are set to work with the Lewers to see if a deal can be reached.

The Lewers said they were not looking for a windfall.

"I think for the public's $14 million, they deserve access," said Bunny Lewers. "The opportunity is there to clean up a mess. It makes sense to do it now."

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.