SIERRA NEVADA RANGE ON THE MOVE, REPORT SAYS.

Byline: Associated Press

The Sierra Nevada mountains are moving - at the rate of about an inch every three years.

That's the conclusion of a report published last week in the journal Nature.

Geologists Craig Jones of the University of Colorado, Jeff Unruh of Walnut Creek and Leslie Sunder of Dartmouth University say in their report that motion may help explain some of the most dramatic features of this part of the world, including the sharp rise and fall of mountain, plain and valley, from Colorado to California.

``If you look at the western United States, on average, its behavior is more like a very dense fluid, like molasses, than a bunch of small rigid pieces of rock,'' said Unruh of William Lettis and Associates in Walnut Creek. ``Really, that's what we wanted to do: Make sense of what we are seeing.''

The geologists used data obtained over three decades to estimate the density and thickness of the continental crust in the West. ``We are the beneficiaries of a lot of hard work by other people,'' Jones said. They also calculated the pull of gravity on the mountain ranges, factoring in height, type of material and whether rising heat from the Earth's mantle, a layer of hot, liquid rock just below the crust, was keeping certain areas more fluid.

The Basin and Range region of Nevada, up to the eastern Sierra, and Colorado's Rio Grande Valley appear to be heated most from beneath, although researchers are still trying to figure out why. The heat seems to be a major factor, though, in how fast a mountainous area flows.

Geologists have puzzled for some time over the spectacular Western landscape. At one time, it was simply thought that all the geologic ups and downs resulted from natural tensions along the edge of a continental plate. The North American plate, underlying this continent, meets the Pacific plate along the edge of California. That junction is best known as the San Andreas Fault.

The two plates grind against each other, moving about six times faster than the Sierra apparently does. And yet, scientists have grown increasingly aware even such an enormous pull is not enough to explain 1,000 miles of deformation in the continental crust.

But a liquid landscape model does. Not only that, but it may also help explain some peculiar earthquake faults that have startled geologists by being where theory said they shouldn't be - including a whole set of deep, buried faults along the western edge of the Central Valley. Scientists are beginning to speculate that those were formed by the slow, steady pressure of the Sierra flowing downward, pushing against the Valley formation.

``The bigger point, of course, is that we're looking beyond plate tectonics for explanations,'' said Jones.