Walden Pond: An endangered treasure

The National Trust for Historic Preservation has listed Walden Pond and Walden Woods, where Henry David Thoreau wrote his 1854 classic “Walden,” one of “America’s 11 Most Endangered Historic Places.” Historian Douglas Brinkley reports on how the Concord, Mass., dam and its surrounding, spiritually nourishing forests—a major part of our national heritage—are threatened by nearby development.