The frontier, both as an ideal and in the physical sense, shows up in both Train Dreams and River of Shadows. In Train Dreams the frontier appears through the protagonist’s job of building railroads through the, at that time, somewhat wild and uncivilized area of America. A large part of the frontier is that it is one step away from no longer being the frontier because it is the “American way” to constantly push forward and develop the unsettled area, such as through building railroads. In River of Shadows the frontier is less about boundaries of land but rather developments in technology. Muybridge creating motion pictures for the first time is an obvious example of this. It is him pushing the envelope and finding something new from what is already there. Just as the frontier of land was developed in Train Dreams so was photographic technology in River of Shadows.