Webber Lake and Lacey Meadows, located at the headwaters of the Little Truckee River, will be opened to the public for the first time in more than 100 years under the agreement.
The Truckee Donner Land Trust and Trust for Public Land, acting together as the Northern Sierra Partnership, bought the land for $8 million from Clifton and Barbara Johnson.
Barbara Johnson, whose family had owned the land for about a century and once used Lacey Meadows for summer sheep grazing, hailed the acquisition.
"Our wishes have been fulfilled, and the legacy of our family will be remembered," she said in a statement. "The beautiful lands we have worked on and care for are, at long last, protected for future generations to enjoy forever."
The two conservation groups say the property is rich in history and natural beauty. It includes 260-acre natural Webber Lake, the historic Webber Lake Hotel, unspoiled, wildflower-dotted meadows and critical habitat for wildlife.
Henness Pass Road, one of the most heavily traveled emigrant routes across the Sierra in the 19th century, runs past the lake. The hotel is the only remaining stagecoach hotel along the route.
"This property has it all," said Perry Norris, executive director of the Truckee Donner Land Trust.
A fishing campground will remain in private hands for four years, then a public campground is planned.
"This will provide exceptional recreational opportunities for people who visit and live in the northern Sierra," said Dave Sutton, northern California director of the Trust for Public Land.
The California Wildlife Conservation Board, Sierra Nevada Conservancy and Northern Sierra Partnership joined many individuals in provided significant funding for the purchase.
It's the latest in a series of acquisitions by the Northern Sierra Partnership to conserve the Little Truckee River watershed. Since its launch five years ago, the partnership has helped conserve over 14,000 acres in the watershed, including Independence Lake, Perazzo Meadows, Webber Falls and the Mt. Lola Trail.
"The Little Truckee watershed is a hidden treasure, little known to the general public," said Lucy Blake, president of the partnership. "Go there and you won't be disappointed."