The Appalachian Mountains (i/ˌæpəˈleɪʃᵻn/ or /ˌæpəˈlætʃᵻn/,[note 1] French: les Appalaches), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians first formed roughly 480 million years ago during the <answer>Ordovician Period</answer> 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.
In what era did the mountains form?
Ordovician Period