North America has been criss-crossed by one immense range of mountains after another throughout its almost four-billion-year history.
A range of mountains may persist for hundreds of millions of years, like the Appalachians. On repeated occasions, the warped, folded rocks of the Appalachians were brought up out of the continent's basement and raised thousands of feet by tectonic forces. If mountains are not continuously uplifted, they are worn down by erosion in a few million years. In North America's geologic past, eroded particles from its mountains were carried by streams and dumped into the continent's inland seas, some of which were as large as the present-day Mediterranean. Those rivers and seas are gone from the continent, but the sediments that filled them remain, like dirt in a bathtub when the water is drained. The roots of all the mountain ranges that have ever stood in North America all still exist, and much of the sand and clay into which the mountains were transformed still exists also, as rock or soil formations.
Various parts of North America were formed all over the world, at various times over four billion years, and were brought together and assembled into one continent by the endless process of plate tectonics.
