The present geology of the northwest quadrant of the Circum-Pacific is the product of the interact- ions between plates or paleo-plates which have oc- curred since the earliest part of the earth's hist- ory. Almost every possible geologic structures are observable there; stable continents, collision belts, and subduction arcs as well as extensional basins. This suggests that almost all the possible tectonic processes occurred through geologic time and the present overall structure of the Quadrant is no more than a time section of the long lasting tectonic history which the region experienced.