This region is one of the most geologically young and tectonically active in North America. The generally rugged, mountainous landscape of this province provides evidence of ongoing mountain-building. The Pacific Mountain System straddles the boundaries between several of Earth's moving plates-the source of the monumental forces required to build the sweeping arc of mountains that extends from Alaska to the southern reaches of South America.

This province is subdivided into several subprovinces, including the active and sometimes deadly volcanoes of the Cascade Range and the young, steep mountains of the Pacific Border and the Sierra Nevada. - USGS