Thursday, January 24, 2013
Exploring A Grand Mystery
Carving Grand Canyon: Evidence, Theory, and Mystery, by Wayne Ranney, is the next logical book to read after the one he co-wrote with Ron Blakey, Ancient Landscapes of the Colorado Plateau. In Ancient Landscapes, the authors describe the environments in which the layers of the Colorado Plateau formed and illustrate those concepts with paleogeographic maps. As you study those maps, you can't help but try to impose the Grand Canyon on them, since it's the feature that best exposes the layers. At what point, you may wonder, does the canyon begin to be carved?
Carving Grand Canyon is the best answer to that question. It narrates the attempt by geologists to formulate a unified theory of how the Grand Canyon formed and how long it took to do so. Once you've started reading it you'll realize that theory is – complicated.
Fortunately, it's also fascinating – a story of rivers and basins, faults and frost wedging, lava flows and karst collapse, personalities and plate tectonics. If you look at a map of the Canyon, from Lee's Ferry to Grand Wash Cliffs, you may suspect that it's not simply a question of how old the Colorado River is (though that's the most pertinent question). It's a question of what else can happen in a region that large, over millions of years during which several unique conditions persist.
One of the most interesting controversies is whether a paleocanyon may have existed, one that continued to be cut down to current levels in parts of the Grand Canyon. The graphic on page 124 beautifully illustrates the argument that a paleocanyon existed in Mesozoic layers above Eastern Grand Canyon that have since eroded away. The relatively new study of karst collapse near the Kaibab Upwarp also sheds some light on the mystery of how the river cut through the southern tip of the upwarp.
This book is for people whose curiosity burns when they look at the Grand Canyon, trained geologists and armchair geologists alike. It is lavishly illustrated with photographs, cross-sections, maps (some of which are paleogeographic), and diagrams that make the text clear and easy to understand. It offers a coherent answer to a question that is far more complicated than it seems. And best of all, it sparks as much curiosity as it satisfies. Buy two copies – one for your reference library, and one to take with you as you explore Grand Canyon, a place with enough wonder to fill a lifetime.