What are the motifs in The Last American Man by Elizabeth Gilbert?

The American Frontier is a recurring idea. In Eustace Conway's own way, he is one of the preservers of the American frontier. Since colonial times, the American frontier was considered to be any place in the new world that was not yet inhabited and beyond the reach of the Europeans. Soon the American frontier became synonymous with the forested interior of the country and what eventually became known as the Wild West.