The next layer is the mantle. Many people think of this as lava, but it's actually rock. The rock is so hot, however, that it flows under pressure, like road tar. This creates very slow-moving ...

John Wesley Powell had more than just a passing interest in the layers upon layers of rocks exposed by the Colorado River. The expedition down the Green and Colorado Rivers, he would later claim ...

Layers of volcanic rock in eastern Oregon, the Willamette Valley and the Columbia Basin have created fertile soil for farming and ranching, but in the future it could provide fruitful ground for a ...