This is a very interesting question. As a geologist who mainly looks at how the surface of the Earth changes through time, I had to do a bit of internet sleuthing to come up with an answer.

First, here is a little bit of background on the origin of the Mar de Cortez. The Sea of Cortez, also known as the Gulf of California, is a unique corner of the Pacific Ocean. This remarkable “young” sea is thought to be around five million years old and home to nearly 900 species of fish and the widest variety of whales and dolphins found anywhere on Earth. It is one of the youngest seas on Earth.

I use “young” in the geologic sense, where we tend to think of Earth’s oceans and mountain ranges forming on the 10 – 100 million year timescales. This is because the tectonic plates on Earth move at very slow rates, millimeters per year, about the same rate that your fingernails grow.

This young ocean basin formed when the North American and Pacific tectonic plates began separating at a mid ocean ridge called the East Pacific Rise. This process of seafloor spreading caused the Earth’s crust to be stretched thin and sink inside the continent and eventually resulted in the Baja peninsula breaking away from mainland Mexico. This plate boundary extends northward as the San Andreas Fault system, where the North American and Pacific Plates are sliding past each other.

Now, the answer to your question.The California coast and western coast of Baja is connected and influenced by the California current that brings cold water from the north, all the way from Alaska (check out this diagram ). This is where things get interesting, and a little more complicated.

The California current flows away from the continent and doesn’t flow into the Sea of Cortez because of the Coriolis effect, and the Sea of Cortez is too small to be affected by lunar tides. But, tides from the rise and fall of the Pacific Ocean pour in and rush out of the Sea of Cortez in a massive movement. The northern end has a 32-foot tidal range, the third largest in North America! Wind-induced currents also cause major movements of water during the winter. The wind drives the water at 3% of the wind speed and transfers as much as 40% of its energy. When water moves away from an island or coastline it is replaced by water from below in a process called upwelling. All this water moving around brings up not only deeper water, from depths of ~1500 ft, but large amounts of nutrients as well. This upwelling and transfer of nutrients is what makes the Sea of Cortez such an amazing place for fish and marine life to flourish, and why it is such an interesting and ecologically diverse place on our planet.

I hope that helps answer your question :)