Mexico is bordered by the United States to the north and Belize and Guatemala to the southeast. Mexico is about one-fifth the size of the United States. Baja California in the west is an 800-mile (1,287-km) peninsula that forms the Gulf of California. In the east are the Gulf of Mexico and the Bay of Campeche, which is formed by Mexico's other peninsula, the Yucatán. The center of Mexico is a great, high plateau, open to the north, with mountain chains on the east and west and with ocean-front lowlands beyond.