Galen Clark (March 28, 1814 – March 24, 1910) was a Canadian-born American conservationist and writer. He was the first European American to document the Mariposa Grove of Giant Sequoia trees. His advocacy contributed to the Yosemite Grant of 1864, which protected the grove and Yosemite Valley under state management. He served as Guardian under the Yosemite Commission from 1866 to 1880, and again from 1889 to 1896 — 21 years in total.

Galen Clark was born in Shipton, Lower Canada (now Quebec) in 1814. He joined the westward migration as a youth and moved to Waterloo, Missouri in 1836.

In Missouri, he met Rebecca McCoy, and they married in 1839. They had five children: Elvira Missouri Clark (1840–1912), Joseph Locke Clark (1842–1862), Mary Ann Clark (1844–1919), Calen Alonzo Clark (1847–1873), and Solon McCoy Clark (1848–1857). Only two survived their parents: Elvira Clark, who married and became a doctor in Oakland, California; and their other daughter, Mary Ann Clark, who married John T. Regan of Springfield, Massachusetts.

After his wife died young, Clark moved to California to seek his fortune in 1854 at the time of the California Gold Rush. In 1857, at the age of 43, Clark contracted a severe lung infection that was diagnosed as consumption. Doctors gave him six months to live, as they had no antibiotic treatment at the time, but counseled rest and outdoor air.

Clark moved to the Wawona area. "I went to the mountains to take my chances of dying or growing better, which I thought were about even." (Galen Clark, 1856) In June 1856, Clark and William Mann explored the area above the Wawona valley and documented the Mariposa Grove of giant sequoias, making Clark one of the first non-indigenous people to visit the grove. Clark spent subsequent years exploring the area and guiding visitors to the sequoias.

He wrote about protecting the grove to friends and the US Congress. He contributed to the writing and passage of legislation to protect the area, gaining support of US Senator John Conness from California. The act for the Yosemite Grant was signed into law by President Abraham Lincoln. Ceding the land to the state of California for preservation, the grant was the first of its kind. The legislation was to protect Yosemite Valley and the Mariposa Grove of Giant Sequoias for "public use, resort, and recreation ... to be left inalienable for all time." Clark was appointed the first guardian of the grant by the Yosemite Commission, the state board created to manage Yosemite Valley and the Mariposa Grove. In 1880 a new California state constitution limiting tenure of office replaced the entire board and Clark with it; he returned as Guardian in 1889 and served until 1896. His lungs healed, and he explored and climbed much of the area.

Clark did not seek to enrich himself from Yosemite Valley or the Sequoia trees. He ran Clark's Station, a modest hotel and guide service at what is now Wawona, providing meals, shelter, and grazing for travelers on the route between Mariposa and Yosemite Valley. The Ahwahnechee people called the site "Pallahchun," meaning "a good place to stop." He sold the property in 1874 to relieve his debts; the buyer, Henry Washburn, later renamed the area Wawona. A poor businessman throughout his life, Clark was constantly in debt. His Clark's Station, for example, had several more employees than required for the number of guests and its short season.

Toward the end of his life, Clark was desperately poor. He wrote three books on Yosemite. These include Indians of the Yosemite (1904), The Big Trees of California (1907), and The Yosemite Valley (1910), the last delivered to the printer less than two weeks before his death. Clark's book on the sequoia trees is simple, factual, and direct. He left out his personal role in the discovery, popularization, and protection of the Mariposa Grove of Big Trees. He served as hotel keeper, guide, and guardian of Yosemite and the Mariposa Grove.