[PAR] [TLE] Appalachian Mountains [SEP] The Appalachian Mountains ( , 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 Ordovician Period.  It once reached elevations similar to those of the Alps and the Rocky Mountains before naturally occurring erosion.  The Appalachian chain is a barrier to east-west travel, as it forms a series of alternating ridgelines and valleys oriented in opposition to most roads running east or west. [PAR] [TLE] Western United States [SEP] The Western United States, commonly referred to as the American West, the Far West, or simply the West, traditionally refers to the region comprising the westernmost states of the United States.  Because European settlement in the U.S. expanded westward after its founding, the meaning of the West has evolved over time.  Prior to about 1800, the crest of the Appalachian Mountains was seen as the western frontier.
[PAR] [TLE] Appalachian Mountains [ SEP ] The Appalachian Mountains ( , 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 Ordovician Period . It once reached elevations similar to those of the Alps and the Rocky Mountains before naturally occurring erosion . The Appalachian chain is a barrier to east - west travel , as it forms a series of alternating ridgelines and valleys oriented in opposition to most roads running east or west . [PAR] [TLE] Western United States [ SEP ] The Western United States , commonly referred to as the American West , the Far West , or simply the West , traditionally refers to the region comprising the westernmost states of the United States . Because European settlement in the U.S. expanded westward after its founding , the meaning of the West has evolved over time . Prior to about 1800 , the crest of the Appalachian Mountains was seen as the western frontier .
Which mountain range, found in eastern North America, was seen as the western frontier prior to about 1800?
Which mountain range , found in eastern North America , was seen as the western frontier prior to about 1800 ?
Appalachian Mountains
Appalachian Mountains