"It's hard to see a river all at once, especially in the mountains. Down on the plains, rivers run in their course as straightforward as time, channeled toward the sea. But up in the headwaters, a river isn't a point where you stand. In the beginnings of the river, you teeter on the edge of a hundred tiny watersheds where one drop of water is always tipping the balance from one stream to another. History changes with each tiny event, shaping an outcome that we can only fully grasp in hindsight. And that view changes as we move farther downstream."