Cooley's Park was taken during one of the expeditions Timothy O'Sullivan made out West in the late nineteenth century in Nevada, Arizona, and Colorado. O'Sullivan was assigned to join Lt. George M. Wheeler on the Geological Surveys West of the One Hundredth Meridian, where he was part of a team required to photograph the topography and towns as well as Native Americans. This image was taken in Arizona, close to the canyons and rock dwellings where several tribes were living at the time.

O'Sullivan's Western photographs represent not only an explorer's first encounter with a startling new terrain, but also an artist's vision of the power of nature, at once threatening and awesome. Traversing American frontiers of land and photography, O'Sullivan encountered the Western wilderness and documented the outposts of an advancing civilization.

Timothy H. O’Sullivan (1840–1882) was one of the most important American photographers of the nineteenth century. Employed by Mathew B. Brady and Alexander Gardner, he made iconic images of the American Civil War. He then served as the official photographer for three U.S. government survey expeditions,  working alongside geologists, naturalists, and surveyors: the Geological Exploration of the Fortieth Parallel (or “King Survey”) of 1867–69 and 1872; the Darien (Isthmus of Panama) Expedition of 1870; and the Geological Surveys West of the 100th Meridian (or “Wheeler Survey”) of 1871 and 1873–74.