Complex sentence: Stegner wrote the foreword and edited "This Is Dinosaur", with photographs by Philip Hyde, a Sierra Club book that was used in the campaign to prevent dams in Dinosaur National Monument and helped launch the modern environmental movement.
Split into simpler sentences: Stegner wrote the foreword to and edited "This Is Dinosaur", with photographs by Philip Hyde. The Sierra Club book was used in the campaign to prevent dams in Dinosaur National Monument and helped launch the modern environmental movement.