Mazatlán is a city in the Mexican state of Sinaloa. The city serves as the municipal seat for the surrounding municipio, known as the Mazatlán Municipality. It is located on the Pacific coast across from the southernmost tip of the Baja California Peninsula.

The Gulf of California, also known as the Sea of Cortés or Sea of Cortez, or less commonly as the Vermilion Sea, 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 that flow into the Gulf of California include the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and the Yaqui. The surface of the gulf is about 160,000 km2 (62,000 sq mi). Maximum depths exceed 3,000 meters (9,800 ft) because of the complex geology, linked to plate tectonics.