Tell your fellow americans that you plan to cross the United States by train, and their reactions will range from amusement at your spellbinding eccentricity to naked horror that they, through some fatal social miscalculation, have become acquainted with a person who would plan to cross the United States by train. Depending how you slice it — time or money — there are either 61 or 960 immediate reasons not to travel by Amtrak trains from New York City to Los Angeles. Those are the extra hours and dollars, respectively, that you might reasonably expect to forfeit if you forgo a six-hour $129 nonstop flight and opt instead for an Amtrak sleeper car. Covering the interjacent 2,448.8 miles can easily consume some 67 hours for a mind-boggling $1,089. Of course, you might remind your quote-unquote fellows, any form of modern engine-based transport, even Amtrak, is preposterously fast compared with the method that Homo sapiens employed to move ourselves and, more important, our tchotchkes for most of our species’ 300,000-year history, which is walking. Crossing the stretch of land where roughly half the Donner party starved, froze or, in the case of the group’s two Miwok guides, were s...