In the spring of 1921, through a coöperative arrangement with the California Fish and Game Commission, the National Park Service instituted a free nature-guide service in Yosemite. The aim of this service was to furnish useful information regarding trees, wildflowers, birds, and mammals, and their conservation, and to stimulate interest in the scientific interpretation of natural phenomena. The means used to attain this aim were: trips afield; formal lectures, illustrated with lantern slides or motion pictures; ten-minute campfire talks, given alternately at the main resorts of the park; a stated office hour when questions regarding the natural history of the park could be answered; a library of dependable reference works, and a flower show where the commoner wildflowers, properly labeled, were displayed. Occasionally, visiting scientists helped by giving lectures. About this same time, a Yosemite ranger, Ansel F. Hall, conceived the idea of establishing a Yosemite museum to serve as a public contact center and general headquarters for the interpretive program. Superintendent W. B. Lewis endorsed the plan, and the old Chris Jorgenson artists’ studio was made into a temporary museum; Hall was placed in charge as permanent educational officer. The same year found a museum program under way in Yellowstone National Park, where Milton P. Skinner was made park naturalist, and in Mesa Verde National Park, where Superintendent Jesse Nusbaum organized a museum to care for the archeological treasures brought to light among the ruins of prehistoric man’s abode. Glacier, Grand Canyon, Mount Rainier, Rocky Mountain, Sequoia, and Zion quickly organized educational programs similar to those established by Yosemite and Yellowstone, and in 1923 Hall, with headquarters in Berkeley, was designated to coördinate and direct the interpretive work in all parks. Working with Dr. Frank R. Oastler, Hall in 1924 organized a comprehensive plan of educational activities and defined the objectives of the naturalist group.