Why the West Is Wild

As a result of a string of remarkable geological discoveries during the past decade, many bewildering features of the earth's surface are being satisfactorily explained for the first time. Most scientists finally agree, for example, that the continents--which look as if they once fitted together like a giant jigsaw puzzle--indeed broke off from one or two immense land masses along volcanically active cracks in the earth's crust known as mid-ocean ridges. Part of this undersea mountain chain, which girdles the earth like stitching on a baseball, has now been identified as the prime suspect in still another major geological mystery: the raw and atypical terrain of the American West.

The new theory, outlined by the University of Toronto's J. Tuzo Wilson, fits in neatly with the tenets of the new geology. As North America slowly crept westward away from the Mid-Atlantic Ridge, Wilson says, the west coast of the continent eventually met up with another segment of the ridge system called the East Pacific Rise. But the moving continent did not stop at this natural barrier; instead it bulldozed right over it. As a result, the West now sits smack atop this hot seam in the earth's crust.

Granite Slabs. Wilson traces the path of the rise (see map) by such subtle evidence as heat flow in rocks, remains of ancient magnetic fields and the variations in the velocity of seismic waves under different parts of the West. He also points to much more conspicuous signs of its presence: the hot springs in California and Yellowstone National Park, the remnants of old volcanoes--Arizona's Kitt Peak, for example, and Crater Lake in Oregon--the upward tilt of the American plains as they stretch westward toward the Rockies and the shape of the mountains themselves. Unlike the Andes or even the closer Canadian Rockies --both of which were squeezed up by massive lateral pressures--the American Rockies seem to have been at least partially lifted by enormous forces directly beneath them. As Geophysicist Wilson points out, many of them are not jagged or irregular peaks, like their Canadian neighbors to the north, but huge granite slabs that still retain the flatness of the original Colorado Plateau.

Do geological events that occurred 30 or 40 million years ago have any contemporary relevance? Wilson is convinced that they do. By carefully studying the rise, he says, scientists may be able to locate more of the rich mineral deposits that were lifted close to the surface. Further analysis of this underground activity may also help explain the slight but puzzling earth tremors that periodically plague Nevada and Colorado, which lie outside the Pacific earthquake belt. Finally, such studies may bring some needed enlightenment about California's San Andreas Fault, a 600-mile crack running through the surface of the earth that was probably created by the underlying rise and may still be affected by it. Could part of California actually split off from the mainland along this seam, as some people fear? Wilson acknowledges that the area west of the fault is edging slowly northward. But he is confident that because the movement is at a less-than-glacial pace of an inch or so a year, California will remain part of the North American continent for millions of years to come.

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