Sea of Cortez geological origins

Modified from NOAA-NGDC image

The Origin of the Sea of Cortez and the Baja California peninsula

Around 4 to 6 million years ago a segment of the East Pacific Rise split the Baja California peninsula from the Mexican mainland, shifting it and much of southern California in a northwesterly direction relative to the rest of North America (Brusca, 1980). The East Pacific Rise is an area where magma from below the earth's crust reaches the earth's surface, and flows outwards, spreading apart the two tectonic plates that it separates. To the east is the American plate, consisting of most of North America, and to the west is the Pacific plate, containing the Baja Peninsula and part of California on its eastern margin. The East Pacific Rise continues up the Gulf, and continues across land as a complex system of transform faults, the most famous being the San Andreas fault. The East Pacific Rise then emerges from the land mass and re-enters the Pacific Ocean off the coast of Oregon. The map at left shows the East Pacific Rise as the newer crustal material (redder color). This seafloor spreading is continually widening the Sea of Cortez, much as the mid-Atlantic ridge is currently widening the Atlantic Ocean basin.