The Colorado plateau is a physiographic region in the southwestern United States that spans the four states of Arizona, Mexico, Colorado and Utah. The plateau is named after the Colorado river (the state itself has little of the plateau), which has, along with its tributaries, side-streams, run-offs and other forces of nature formed the canyons the region is famous for: Grand Canyon in Arizona, Zion and Bryce in Utah and hundreds of others, perhaps not as grand as these but just as beautiful. Why is the Colorado River such a great carver of canyons, while the Mississippi that runs longer is not? I overheard a ranger at the Grand Canyon National Park give a succinct answer: the Colorado has a sharp gradient owing to its descent from the Rockies, and also carries much grit – cutting power – in the form of rocks. The river runs into the elevated Colorado plateau that is brittle on account of its aridity, and cuts through it, chipping a little of the plateau every year. It has taken over five million years, a length of time too hard for us to imagine but that is not more than a blink of an eye in geological terms, for something of such magnificence as the Grand Canyon to form. There is, of course, much pooh-poohing of this theory – You’re telling me a river caused this? – and there should be, for even geologists do not concur on this topic, and theories do change over time, the newest ones overriding the existing ones.