The Gulf of California (also known as the Sea of Cortez or Sea of Cortés or Vermilion Sea; locally known in the Spanish language as Mar de Cortés or Mar Bermejo or Golfo de California) is a body of water that separates the Baja California Peninsula from the Mexican mainland. It is bordered by the states of Baja California, Baja California Sur, Sonora, and Sinaloa with a coastline of approximately 4,000 km (2,500 mi). Rivers which flow into the Gulf of California include the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and the Yaqui. The gulf's surface area is about 160,000 km2 (62,000 sq mi).
The Gulf is thought to be one of the most diverse seas on the planet, and is home to more than 5,000 species of macro-invertebrates. Home to over a million people, Baja California is one of the longest peninsulas in the World, second only to the Malay Peninsula in Southeast Asia. The Gulf of California is a UNESCO World Heritage Site.
Even though the shores of the Gulf of California are generally sheltered from the continuous wave shock that is experienced by most other North American shores, storms known as a “chubasco” can cause significant damage to shorelines, despite their brevity.
Geologic evidence is widely interpreted by geologists as indicating the Gulf of California came into being around 5.3 million years ago as tectonic forces rifted the Baja California Peninsula off the North American Plate. As part of this process, the East Pacific Rise propagated up the middle of the Gulf along the seabed. This extension of the East Pacific Rise is often referred to as the Gulf of California Rift Zone. The Gulf would extend as far as Indio, California, except for the tremendous delta created by the Colorado River. This delta blocks the sea from flooding the Mexicali and Imperial Valleys. Volcanism dominates the East Pacific Rise. The island of Isla Tortuga is one example of this ongoing volcanic activity.
The narrow sea is home to a unique and rich ecosystem. In addition to a wide range of endemic creatures, such as the critically endangered vaquita, it hosts many migratory species, such as the humpback whale, California gray whale, killer whale, manta ray and leatherback sea turtle, and the world's largest animal, the blue whale. The unusual resident populations of fin whales and sperm whales do not migrate annually. This region has historically been a magnet for world-class sport fishing activities, with a rich history of sporting world records.
The region also has a rich history as a commercial fishery. However, the data vary wildly according to the species being studied, and the Gulf's ability to recuperate after years of overfishing remains uncertain. Moreover, changes in terrestrial ecology, such as the vast reduction in flow from the Colorado River into the Gulf, have negatively affected fisheries, particularly in the northern region.
The Gulf of California sustains a large number of marine mammals, many of which are rare and endangered. Its more than 900 islands are important nesting sites for thousands of seabirds, and its waters are primary breeding, feeding, and nursing grounds for myriad migratory and resident fish species. For decades, the gulf has been a primary source of two of Mexico
's leading marine resources, sardines and anchovies. Water pollution is a problem in the Gulf of California, but the more immediate concerns are overfishing and bottom trawling, which destroys eelgrass beds and shellfish.
The Gulf of California contains 37 islands – the two largest being Isla Ángel de la Guarda and Tiburón Island. Most of the islands are found on the peninsular side of the gulf. In fact, many of the islands of the Sea of Cortez are the result of volcanic explosions that occurred during the early history of Baja California. The islands of Islas Marías, Islas San Francisco, and Isla Partida are thought to be the result of such explosions. The formations of the islands, however, are not dependent on each other. They were each formed as a result of an individual structural occurrence. Several islands, including Isla Coronado, are home to volcanoes.