Galen Clark 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.