Here's a breakdown:

* Convergent Plate Boundary: This type of boundary occurs when two tectonic plates collide. In the case of the Cascade Range, the Juan de Fuca Plate (oceanic) is subducting beneath the North American Plate (continental).

* Subduction: As the denser oceanic plate (Juan de Fuca) dives beneath the continental plate, it melts due to the immense pressure and heat. This melted rock (magma) rises to the surface, erupting as volcanoes and creating the Cascade Range.

So, the Cascade Range is a classic example of a volcanic mountain range formed by the forces of plate tectonics and subduction.