In August 1916, the US Congress created the National Park Service to protect America's finest landscapes and encourage people to visit them. One of the inspirations for the Park Service was the work of the Scottish-born naturalist, John Muir, whose lyrical writings about the Yosemite Valley gained huge popularity. Simon Watts tells John Muir's story through readings from his work and contributions from Mary Colwell, author of "John Muir: The Scotsman who saves America's Wild Places".PHOTO: John Muir (Getty Images).NOTE: The wildlife audio in this programme is used courtesy of the National Park Service, the National Audubon Society and Kevin Colver.