Mature and Youthful Landscapes in the United States

July 20, 2012


: Thomas McGuire 
Summary Author: Thomas McGuire

The rounded, mature landscapes of the Appalachian Mountains in the eastern U.S. contrast with youthful and dramatic landscapes of the West, including the Rocky Mountains. Both mountain regions were formed in response to collisions of Earth’s tectonic plates. But unlike the ancient Appalachians, plate motions that created the Rockies, and other mountains of the American West, continue today.

For the most part the uplift of the Appalachian Mountains ended about 250 million years ago. Since then erosion has been the dominant force shaping the Appalachians. This includes numerous advances of continental glaciers. In fact, the Hudson Highlands (shown in the upper image) were overtopped by glaciers -- by as much as 1 mi (1.5 km) of ice and rubble.

The Rocky Mountains formed much more recently as illustrated below by the Collegiate Peaks of the Sawatch Range in Colorado. Furthermore, recent glaciers were restricted to mountain valleys and the highest peaks were not completely entombed in ice. This is why such dramatic peaks characterize the Rockies. Upper Photo: New York, U.S (taken in mid 1990s); Lower photo: Colorado, U.S. (taken in 2005). [Revised August 2017]