Photograph by James P. Blair, National Geographic Published
March 2, 2011 A tough hunk of rock that may be under Wyoming
could solve the mystery of how the Rocky Mountains formed,
according to a new idea that explains why some mountain ranges
exist farther inland than expected. Normally mountains form
close to coastlines, in places where oceanic plates dive—or
subduct—under continental plates (get an overview of plate
tectonics). But at about 620 miles (1,000 kilometers) inland,
the North American Rockies (see map) are unexpectedly far east
from the tectonic collision point. The prevailing hypothesis for
the Rockies' birth, called flat-slab subduction, says that the
Pacific oceanic plate dove underneath the North American plate
at an unusually shallow angle. But about 70 million years ago,
the diving plate mysteriously rose and started to scrape along
the continent's underside, generating friction that pushed up
the mountains. Watch video of the flat-slab theory for making
the Rockies. The new theory doesn't