Insular Islands

They probably formed as a composite of several volcanic chains near the equator, offshore of continental landmasses, by the Carboniferous Period around 300-325 million years ago.

This violent collision halted subduction which fed volcanic activity in the Omineca Arc and closed the Bridge River Ocean.

The subduction zone moved westward to the Farallon Trench, causing new volcanism which formed the Coast Range Arc.

Rocks of the Insular Islands now comprise wide sections of the westernmost coast of the North American plate.

This extends to the northern North Cascades range in Washington State, perhaps as far as the Wallowa Mountains in northeastern Oregon which may be a displaced fragment from the Insular Belt.