Insular Islands

The Insular Islands were an arc of volcanic islands that stood in what is now the Pacific Ocean through the Paleozoic and Mesozoic eras, built by subduction and melting along the Farallon Plate at the edge of the Insular microplate, likely forming as a composite volcanic chain near the equator around 300 to 325 million years ago in the Carboniferous period. About 115 million years ago, in the mid-Cretaceous, the chain collided with and fused onto the North American Plate; its remnants now form part of western North America's coast, including the Insular Mountains of southeast Alaska, Haida Gwaii, Vancouver Island, and sections of the North Cascades in Washington state.