Final answer:
The Cascade Mountain Range (including Mt. St Helens) is an example of a convergent plate boundary where the North American Plate is converging with the Juan de Fuca Plate.
Step-by-step explanation:
The Cascade Mountain Range, which includes Mt. St. Helens, is an example of a convergent plate boundary. A convergent plate boundary occurs when two tectonic plates collide or move towards each other. In the case of the Cascade Mountain Range, the North American Plate is converging with the Juan de Fuca Plate.
Learn more about Plate tectonics