The Appalachian Mountains ( or , ), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians first formed roughly 480 million years ago during the  Ordovician Period and once reached elevations similar to those of the  Alps and the Rocky Mountains before they were eroded. The Appalachian chain is a barrier to east-west travel as it forms a series of alternating ridgelines and valleys oriented in opposition to any road running east-west.