The answer depends on where you are looking at the Appalachians!

* In the United States: West of the Appalachian Mountains lies the Mississippi River Valley, which stretches all the way to the Rocky Mountains. This region includes the Great Plains, the Midwest, and the Gulf Coast.

* In Canada: West of the Appalachian Mountains in Canada is the Canadian Shield, a vast, rocky area.

So, the answer is: It depends on the location!