Answer:
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Step-by-step explanation:
Both were formed from overthrusting. Overthrust mountains are formed when one tectonic plate crumples over on top of the old rock that lay in its path. The Rockies were formed when the N. American plate moved westward and the plate in its path was shoved on top of N. America.
The Andes are also overthrust mountains, but unlike the Rockies there are extinct, dormant and active volcanoes in the Andes. The tallest of these is Ojos del Salado, which peaks at over 22k feet asl. It lies in the southern volcanic belt of the Andes on the border of Chile and Argentina. There are 3 other volcanic belts in the Andes.
The Andes appear to be newer than the Rockies. They are more seismically active, they have active volcanoes in them and they are much higher, indicating that not enough time has elapsed to erode them very much.