What is the setting of A Canticle for Leibowitz by Walter M. Miller, Jr.?

A Canticle for Leibowitz by Walter M. Miller, Jr., is set in the vast, arid, and desolate vistas of the American Southwest whose conditions are heightened by a nuclear holocaust in the late 20th century. The "Flame Deluge" throws humankind back to hunter-gatherer economies, with some chieftains beginning to think of spreading power to neighbors as the novel opens in the 26th century.