The Gulf of 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 micro-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.