Range Creek

Utah rancher Waldo Wilcox and his family kept this archaeological site secret for 50 years.

He sold the land to a non-profit organization in 2001, and, in 2004, the story became public. From the March Smithsonian magazine:

Part of the excitement rests on hopes that Range Creek may help explain what happened to the Fremont. Along the canyon floor, traces of large villages indicate a flourishing settlement, while pit houses and granaries built high in the cliffs suggest a defensive retreat. "We’ve seen places where people were living in knife-edge ridges, 900 to 1,000 feet above the valley floor, which means to get a jug of water you’d have to send someone on a big long hike and back up," says Jones. "These people were afraid of something. They were obviously trying to protect their food, and it wasn’t from mice."

Cool story. More here (with nice photos).