A wetlands-rich section of private forest near the Cascade foothills — a place where bird-watchers have been able to spot more than 60 species in two hours' time — will be among hundreds of acres near Black Diamond protected from development by a complicated land deal announced yesterday.

Plum Creek Timber yesterday agreed that Ravensdale Ridge, a 1,600-acre slope in southeast King County popular with horse riders and mountain bikers, will continue to be logged in perpetuity, instead of being paved for new homes or businesses.

And hundreds of additional acres in and around Black Diamond, some public and some private, will be set aside for parks and open space.

In exchange, 329 acres of Plum Creek land that had been outside Black Diamond will be annexed to the city so the timber company can develop it. The plans for the development haven't been ironed out.

"Black Diamond is a rural town, and this would still fit within the character of the community," said Karen Wolf, a policy adviser to King County Executive Ron Sims. "But it certainly offers [Plum Creek] a lot more potential for development."

Jason Paulsen, city administrator for Black Diamond, said the deal had been about a decade in the making. "This was a large part of what we hoped to hold on to in order to retain our rural character and remain a unique community," he said.

The Ravensdale Ridge area, just outside the city, is home to Buck Lake, a popular trout-fishing spot, and overlooks Rock Creek, a tributary of the Cedar River.

The ridge is covered with miles of trails and rises high enough that visitors can see the Olympic Mountains to the west and peek-a-boo views of Seattle's skyline.

Under the deal, the land can be logged but never developed. And it must remain open to the public.

Yesterday's complex transaction was worked out between the city, the county, Plum Creek and the Cascade Land Conservancy, a group that tries to protect land from development that often acts as a broker in such deals.

In addition to the Ravensdale land, the deal sets aside several smaller parcels for public use. One of them, King County's undeveloped 165-acre Sawyer Lake Park, will be mostly deeded to Black Diamond, which plans ultimately to rebuild it into a working public park.

Steve Dunphy, spokesman for the Cascade Land Conservancy, said this is a small example of the kind of deals the conservancy hopes to promote in coming decades. It will be trying to persuade community leaders to invest $7 billion over the next century to set aside more than 1 million acres in the Puget Sound region, Dunphy said.

And yesterday's transaction may only be the start for Black Diamond.

The federal government tentatively has agreed to consider matching yesterday's conservation effort at Ravensdale with a $3.6 million grant for the purchase of a few thousand acres of additional forestland near Black Diamond yet to be specified.

"This agreement is really just a big first step," city administrator Paulsen said.

Craig Welch: 206-464-2093 or cwelch@seattletimes.com