Three years ago, in the course of thirteen months, the photographer Peter McBride and the writer Kevin Fedarko hiked from one end of the Grand Canyon to the other. They did it in eight sections, mainly so that McBride could shoot in different seasons. In all, it took them seventy-one days to cover two hundred and seventy-seven river miles and some eight hundred shoe-leather miles, through some of the continent’s roughest hiking terrain—“a whole lot of scratching around the rock puzzles in that giant abyss,” as McBride put it recently.