As the Gulf of California expands, its seafloor does sink or deepen. The current site of the Gulf was previously above sea level, and some parts may have been as high as the 1,800-meter-tall (6,000-foot-tall) Laguna Mountains east of San Diego.
The Gulf of California initially formed about 15 million years ago when the western margin of the North American continent was stretched and thinned, creating a depression between Baja California and mainland Mexico. As this extension continued, it led to rifting of the continent and created a long, narrow fissure in the earth’s lithosphere — the part of the solid earth that includes the crust and the upper mantle. This rifting further separated Baja California from mainland Mexico and submerged the area in between them.
New seafloor crust in the Pacific Ocean is on average 2,500 meters (8,200 feet) below sea level. Seafloor crust gets deeper as it gets older because it gets thicker and heavier, and thus much of the vast expanse of the old Pacific seafloor is deeper than 4,000 meters (13,100 feet). In contrast, the seafloor crust in the Gulf of California is young, less than 7 million years old, and contains broken pieces of continental landmass that are at times only a few hundred meters below sea level.
Additionally, the gulf is almost entirely surrounded by land that pours sediments into its confined area, covering and adding height to the seafloor. As the gulf expands, sediments coming from land are dispersed thinly over a large area.
-— Pat Castillo, geologist and professor, Geosciences Research Division
To learn more about how the Gulf of California is changing, read our story “Birth of an Ocean” at explorations.ucsd.edu/Features/2009/Birth_of_an_Ocean/.