Steven St. Clair, principal of Newport Beach-based St. Clair Co., had entitlements to build up to 1,550 upscale homes and some commercial space on the environmentally sensitive patch of rustic Coal Canyon. The rugged land is the last link for mountain lions and other wild animals to travel between Cleveland National Forest and Chino Hills, so building on the parcel could have spelled their doom.

St. Clair, an avid hiker and mountain-biker, says he didn't know about the parcel's ecological importance when he and some partners bought the land in 1997. But he changed his mind about developing the parcel after talking with conservationists and government wildlife agencies.

Though the property was appraised at $50 million last year, St. Clair agreed to accept $40 million because that's all that environmental groups could raise from donors and government agencies. By officially turning the property over to state parks officials on Tuesday, St. Clair also forgoes an estimated $350 million he originally expected to make in lot sales to merchant builders.