Timothy O’Sullivan apprenticed in the Washington, D.C., portrait studio of Mathew Brady, and he matured and was tested under the most trying conditions as a field photographer during the Civil War. As a result, he was perfectly suited to participate in the postwar government-sponsored surveys of the American West. From 1867 to 1873, he accompanied expeditions that charted the geology and natural resources of the Southwest, sites for future settlement, militarily useful information about the topography and indigenous populations, and the route of the transcontinental railroad. In 1873, he led a side mission to the ancient Anasazi ruins at Canyon de Chelly, in what is now northeastern Arizona. Many photographers have since returned to photograph the so-called White House, fifty feet above the canyon floor, but none has surpassed O’Sullivan’s sweeping depiction of man’s ancient traces tucked in a niche of the steep, striated cliff.