Henry David Thoreau’s classic Walden; or, Life in the Woods (1854) helped establish the nature writing tradition in the US and deeply impacted environmental thought. Influenced by transcendentalist ideas of self-reliance and spiritual communion with nature, Thoreau retreated to land owned by Ralph Waldo Emerson on Walden Pond from 1845 to 1847. “I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach.

This photograph shows the influential naturalist John Muir (r.) and writer John Burroughs (l.) at the Grand Canyon. Muir helped establish the national park system, believing that exposure to wilderness encouraged people to preserve it: “If every citizen could take one walk through this reserve, there would be no more trouble about its care; only in darkness does vandalism flourish.” Muir was a founder of the Sierra Club in 1892.

In 1864 George Perkins Marsh, an influential politician, versatile scholar, and conservationist, advanced an idea revolutionary for its time: “Man is everywhere a disturbing agent. Wherever he plants his foot, the harmonies of nature are turned to discords.” His book Man and Nature; or Physical Geography as Modified by Human Action was groundbreaking for centering human agency in environmental discourse; that our choices transform nature negatively as well as positively. The park bears his name.

The celebrated naturalist John Burroughs promoted a reverence for nature and sustainable land stewardship. He warned in 1908, “One cannot but reflect what a sucked orange the earth will be in the course of a few more centuries. Our civilization is terribly expensive to all its natural resources...and soon how nearly bankrupt the planet will be!” Burroughs helped make nature writing a favorite literary genre of the period. His final home, Woodchuck Lodge, located in the park, is open seasonally.

On May 15, 1903, President Theodore Roosevelt (5th from l.) camped with naturalist John Muir (4th from r.) beneath the “Grizzly Giant,” the most famous giant sequoia tree in California’s Mariposa Grove. Roosevelt persuaded Congress to add the Grove to Yosemite National Park (1906). His bold conservationist agenda included establishing the U.S. Forest Service (1905) to manage forest reserves and signed the Antiquities Act (1906), granting the president authority to designate national monuments.

George Bird Grinnell, a NYC-based naturalist and author, known as “the father of American conservation,” promoted wildlife protection during the late 1800s and helped establish Montana’s Glacier National Park (1910). Editor of the popular sport-hunters’ magazine Forest and Stream, Grinnell advocated various conservation causes. He helped found influential conservation organizations, including the first Audubon Society, the Boone and Crockett Club, and the American Game Protective Association.

Writer Mary Hunter Austin (1868–1934) found refuge in the California desert’s Owens Valley. Inspired by flora and fauna thriving in inhospitable environments, Land of Little Rain (1903) emphasizes cultural reasons for conservation. Settling in NM in 1924, she reflected, “Man is not himself only....He is the land, the lift of its mountain lines, the reach of its valleys; his is the rhythm of its seasonal processions, the involution and variation of its vegetal patterns.” Learn more at the museum.

Gifford Pinchot was a key voice for environmental conservation at the turn of the 20th c. Heading the newly created U.S. Forest Service (1905–10), he charted a path between preservationists, who wanted wilderness lands to be set aside, and business leaders, who wanted unlimited access to extract resources. He viewed the environment as a resource that must be sustainably managed by the government for “the greatest good to the greatest number for the longest time.”

Aldo Leopold began contemplating an ecological approach to conservation in the 1920s. In A Sand County Almanac (1949), he describes his influential “land ethic,” a philosophical basis for mid-20th c. environmentalism. “Examine each question in terms of what is ethically and esthetically right, as well as what is economically expedient,” Leopold argued. “A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.”

Marjory Stoneman Douglas fought to protect the Everglades. Moving to Florida in 1915, she became active in progressive conservationist causes. Initially she argued that development should accommodate the region’s distinct environment. She became more ecological while researching her bestselling book, The Everglades: River of Grass (1947). She highlighted the interconnectedness of the water, land, vegetation, and animals of the Everglades and the threats posed by drainage, dumping, and fill.

George Washington Carver (l.), was the leading African American agricultural scientist of the 20th c. As head of the Agricultural Department at Alabama’s Tuskegee Institute (1896–43), Carver argued that sustainable environmental improvement was essential for strengthening the economic and social circumstances of impoverished Southern Black farmers. He wrote, “A poor soil produces only a poor people—poor economically, poor spiritually and intellectually, poor physically.”