* The San Andreas Fault doesn't directly form mountains. While it's a major geological feature in California, the San Andreas Fault is a transform fault where two plates slide horizontally past each other. This creates earthquakes, not mountains.

* The Andes Mountains are the mountain range along the western edge of South America.

* The Nazca Plate is subducting beneath the South American Plate. This process of subduction is what's driving the formation of the Andes Mountains.

In short, the Nazca Plate is subducting beneath the South American Plate to form the Andes Mountains.