This chapter demonstrates how John Muir’s association with Yosemite defined its significance as a National Park and played a key role in the formation of modern environmentalism. Muir was deeply influenced by Wordsworth, Thoreau, and Burns and by the model of the landscape of genius in general. Muir represented nature in Yosemite as a form of high culture, analogous to the fine arts, in ways that defined the National Park as an institution and have exerted massive influence on modern discourses of nature. That high-cultural version of nature then shaped the American environmental movement, especially through the long political struggle from 1907–13 over the proposal to dam the Hetch Hetchy Valley as a reservoir for the city of San Francisco. In that struggle, Muir and his allies embraced many of the same forms of environmental rhetoric of the landscape of genius initiated by earlier attempts to preserve Wordsworth’s Lake District: a transatlantic connection that launched the American environmental movement and evolved into a hegemonic form of twentieth-century environmentalism.