The Gulf of California (also known as the Sea of Cortez, Sea of Cortés (named for Spanish Conquistador Hernán Cortés) or Vermilion Sea; locally known in the Spanish language as Mar de Cortés or Mar Bermejo or Golfo de California) is a marginal sea of the Pacific Ocean 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). Depths range from fording at the estuary near Yuma, Arizona, to in excess of 3,000 meters (9,800 ft) in the deepest parts.
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 micro-invertebrates.
Home to over a million people, Baja California is the second-longest peninsula in the world, after the Malay Peninsula in Southeast Asia.
The depth of the water helps to determine its temperature. For example, shallow depths are directly influenced by the local temperature of the air, while deeper waters are less susceptible to changes in air temperature. The temperature of the water in the Gulf of California generally experiences lows of 16 °C (61 °F) in winter and highs of 24 °C (75 °F) in summer. But temperatures can vary greatly in the gulf, and the water is almost always warmer by the coast than the open ocean. For example, the waters surrounding La Paz reach 30 °C (86 °F) in August, while the waters in neighboring city Cabo San Lucas, only reach 26 °C (79 °F).
Occasionally, the northern Gulf of California will go through significantly cold winters. The water in the Northern Gulf can sometimes drop below 8 °C (46 °F), which can lead to a large die-off of marine organisms. The animals most susceptible to the large decrease in water temperature include macroscopic algae and plankton.
Giant Pacific manta ray
The narrow sea is home to a 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, Humboldt squid 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. The area near the delta of the Colorado river has a small remnant population of the totoaba fish. This region has historically been a magnet for world-class sport fishing activities .
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.
UNESCO World Heritage Site. Conservation of the Gulf's fisheries and coastlines i San Felipe, San Carlos, Sonora, Cabo San Lucas, La Paz, Loreto, Guaymas, Bahía Kino, Puerto Peñasco, Topolobampo and Mulegé.