Stegner joined the conservation movement in the 1950s while fighting the construction of a dam on Dinosaur National Monument’s Green River. In 1960, he wrote his famous Wilderness Letter on the importance of federal protection of wild places. This letter was used to introduce the Wilderness Act, which established the National Wilderness Preservation System in 1964.In an excerpt from the letter, Stegner wrote: "Something will have gone out of us as a people if we ever let the remaining wilderness be destroyed; if we permit the last virgin forests to be turned into comic books and plastic cigarette cases; if we drive the few remaining members of the wild species into zoos or to extinction; if we pollute the last clear air and dirty the last clean streams and push our paved roads through the last of the silence, so that never again will Americans be free in their own country from the noise, the exhausts, the stinks of human and automotive waste . . . ”