* Plate Tectonics: The Earth's continents are situated on massive plates that are constantly moving. The west coast of the United States is located on the boundary of the North American Plate and the Pacific Plate. These plates are converging (colliding), which causes:

* Subduction: The denser Pacific Plate slides under the North American Plate, creating mountains and volcanoes.

* New Crust Formation: Magma from the mantle rises to the surface, creating new oceanic crust along the mid-ocean ridge. This new crust is relatively young.

* East Coast: The east coast of the United States is situated on the interior of the North American Plate. This area is relatively stable and doesn't experience the same level of tectonic activity as the west coast. The crust here has had more time to cool and solidify, making it older.