Nearly 20,000 acres of remote forest once targeted for vineyard development in remote northwest Sonoma County will be set aside as timberland and wildlife habitat under a landmark conservation deal that closed Friday.

The property commonly called Preservation Ranch near the town of Annapolis is now owned by The Conservation Fund, a national group that specializes in forest protection. It led the $24.5 million purchase — aided by $14 million in state and Sonoma County open space funds.

The conservation deal, the largest by acreage in Sonoma County history, secures the southernmost piece of a 58,000-acre former commercial timber holding — now entirely owned by The Conservation Fund — and assures a vast area of the rugged coast range will remain largely undeveloped and wild, officials said.

"It's like getting to the summit," said Chris Kelly, The Conservation Fund's California program director, who confirmed the sale was finalized Friday.

The acquisition was quietly negotiated last year and made public in February. It puts a quick end to one of the county's biggest land-use fights, a dispute that embodied the broader battle over the spread of Wine Country into North Coast forests.

CalPERS, the giant state workers pension fund, has controlled the 19,645-acre property for nearly a decade. Through a Napa vineyard development firm, it backed a highly controversial proposal to clear nearly 1,800 acres of redwood, fir and oak forest for premium wine grapes.

Local environmentalists and others rallied for years against the project, generating significant political opposition and regulatory hurdles that ultimately may have forced CalPERS to reconsider.

"We were going to take this to the streets," said Chris Poehlmann, president of Friends of the Gualala River, one of several local and national environmental groups that led the charge against the project.

Poehlmann hailed the deal and the "rest and recovery" he hoped it would provide for the former commercial timberland.

"These forests have done their duty," he said.

Wine industry sources said other key factors underlying the sale were the effect of a moribund economy on market demand for premium wine grapes and the mounting cost of the project — with studies and other work said to total more than $2 million last year — combined with Cal-PERS' massive investment losses in the recession and its subsequent move to unload under-performing real estate holdings.

"There were so many ways that it was going to fail," Nick Peay, an Annapolis vineyard owner and premium winemaker, said of the project's political, financial and logistical challenges. "They had to get someone to buy it."

Beyond confirming the sale Friday, CalPERS representatives have declined to comment on the deal. Premier Pacific Vineyards, the Napa development firm backed by Cal-PERS, bought the property in 2004 for $28.5 million.

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 steelhead trout and coho salmon, while mountain lions, bobcats and deer roam the land.

The Conservation Fund, based in Virginia, plans to manage it for sustainable timber operations and sale of carbon credits. It is contributing $6 million and has secured $3.5 million in financing. The property will remain on the tax rolls.

The state Coastal Conservancy, a public agency, last month approved $10 million toward the deal, and the taxpayer-supported Sonoma County Agricultural Preservation and Open Space District contributed $4 million in exchange for an easement that erases development potential and restricts use of the property to sustainable forestry, grazing and public recreation.

Sonoma Land Trust, the Santa Rosa-based nonprofit group, is contributing $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.

That work, set to take about two years, along with studies of the property's forest and streams, will begin immediately, said Kelly, of The Conservation Fund.

"All those things will begin Monday morning," he said.