The Cascade Range, located in the northwestern United States, is one of the most well-known examples of a volcanic mountain range formed by the subduction of one tectonic plate beneath another. Specifically, the plate boundary associated with the Cascade Range is the Juan de Fuca Plate being subducted beneath the North American Plate.
The Cascadia Subduction Zone is the region where this interaction occurs. It's characterized by a convergent plate boundary, where the oceanic Juan de Fuca Plate moves eastward and descends beneath the continental North American Plate. This subduction process leads to various geological phenomena, including volcanic activity, which has resulted in the formation of several active volcanoes in the Cascade Range, such as Mount St. Helens, Mount Rainier, and Mount Adams.
If you were to examine a globe, you would find the Cascade Range along the western edge of the North American continent, with the Pacific Ocean to the west and the Sierra Nevada range to the south. The subduction zone extends from northern California up through British Columbia in Canada.