Researchers say that if it weren't for the hot rocks below Earth's crust, mile-high Denver would be 727 feet below sea level.
In fact, the researchers at the University of Utah say that without those hot rocks, most of the United States would disappear, except for some major Western mountain ranges.
Graduate student Derrick Hasterok says researchers have failed to appreciate how heat makes rock in the continental crust and upper mantle expand to become less dense and more buoyant.
He and professor David Chapman published their findings in the June online issue of Journal of Geophysical Research-Solid Earth.
They say heat inside the planet accounts for half the reason land rises above sea level or higher to form mountains.