The Coast Belt includes the Coast and Cascade mountains and the Fraser Lowland south and east of the city of Vancouver. The mountains form a rugged wall that extends from northwestern Washington state to the Yukon. It is penetrated from the west by long, deep, marine inlets, or fjords, that were carved by glaciers descending from the mountains mostly during and following continental glaciation over 12,000 years ago. The bedrock is mainly (80%) granitic rock that was intruded and cooled deep within the crust as discrete bodies of molten rock (variously called "plutons", or if they are very large, "batholiths") at various times between the Middle Jurassic and early Tertiary (170 to 45 million years ago). Generally the older granitic rocks are towards the ocean and the younger ones are landward. Combined, these intrusions make up one of the largest granitic masses in the world that has been called the "Coast Plutonic Complex". Between the intrusions are "screens" of metamorphosed, folded and faulted volcanic and sedimentary rock. Most are equivalent to the unmetamorphosed strata in the Insular Belt to the west, and some to the rocks of the Intermontane Belt in the east.

The granitic rocks of the Coast Belt probably represent the roots of successive chains of deeply eroded volcanoes, with younger ones built upon older ones. Only the youngest volcanoes (less than 3 million years old), such as Mount Baker in northwestern Washington or Mount Garibaldi northeast of Squamish, preserve the original volcanic landforms.