In many places it is.
Western North America is more mountainous.
The western side of North America is more mountainous.
Western North America is the most mountainous part of North America.
western North America
Western North America is more mountainous.
Although both sides are both mountainous, the western side of the US has a much more mountainous landscape. But it is mostly the Northern Butte side.
western
Western.
EAstern :)
The western part of North America since it is where the Rocky Mountains are.
Northwestern North America has higher elevation than Southeastern North America. Northwestern North America is mainly mountainous while Southeastern North America is mainly flat.
Because that is how it was formed there is more mountains there.