Sierra Club executive director David Brower and others protest plans to dam the Colorado River in Grand Canyon National Park, 1966. The percentage of Americans troubled by rampant pollution more than doubled between 1965 and 1970. By Nixon’s second year in office nearly 70% of Americans thought pollution was a serious problem, and membership in environmental groups, such as the Sierra Club, exploded.

Photo by Arthur Schatz/The Life Picture Collection/Getty Images