Timothy H. O'Sullivan (1840–1882) was a photographer for two of the most ambitious geographical surveys of the nineteenth century. He traversed the mountain and desert regions of the western United States under the command of Clarence King and Lt. George M. Wheeler for six seasons between 1867 and 1874. O'Sullivan developed a forthright and rigorous style in response to the landscapes of the American West. He created a body of work that was without precedent in its visual and emotional complexity, while simultaneously meeting the needs of scientific investigation and western expansion.