John Muir is shown in this circa 1860s image issued by the Wisconsin Historical Society. The society is publishing a rare collection of letters written by Muir on the society's Web site. The letters span more than 50 years of Muir's life, documenting in his own words how he evolved from a strict Calvinist at the University of Wisconsin-Madison to a mountain-climbing, tree-hugging advocate for all things nature. (AP Photo/Wisconsin Historical Society) Greatest Californian: John Muir, shown in a circa 1860s image from the Wisconsin Historical Society, made saving the Sierra Nevada the focus of his conservation efforts.
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