Mexico's Gulf of California has long been known as the Sea of Cortez in a nod to the Spanish explorers who opened up the continent to Europe. Described as the world's fish trap, this rich sea once derived much of its bounty from the Colorado River, which provided nutrients while its delta acted as a huge nursery for sea life. The gulf separates the Mexico mainland from Baja California, which also serves as a U.S. playground with a colorful past.