In the 1860s and 70s, photographer Timothy O'Sullivan created some of the best-known images in American History. After covering the U.S. Civil War, (many of his photos appear in this earlier series), O'Sullivan joined a number of expeditions organized by the federal government to help document the new frontiers in the American West. The teams were composed of soldiers, scientists, artists, and photographers, and tasked with discovering the best ways to take advantage of the region's untapped natural resources. O'Sullivan brought an amazing eye and work ethic, composing photographs that evoked the vastness of the West. He also documented the Native American population as well as the pioneers who were already altering the landscape. Above all, O'Sullivan captured -- for the first time on film -- the natural beauty of the American West in a way that would later influence Ansel Adams and thousands more photographers to come.