Gulf of Mexico numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River and Rio Grande in the northern gulf, and the Grijalva and Usumacinta rivers in the southern gulf. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach. The Gulf of Mexico is an excellent example of a passive margin. The continental shelf is quite wide at most points along the coast, most notably at the Florida and Yucatán Peninsulas. The shelf
Gulf of Mexico basin evaporite sediments deposited after the opening of the Gulf of Mexico has become the Florida Platform. Salt in the Gulf of Mexico can be divided into two main regions: the Northern Gulf of Mexico salt basin and the Campeche salt basin; interpreted to have formed simultaneously. Also referred to as the Louann and the Yucatan Salt basins. Salt deposition in the Gulf of Mexico is poorly dated; the Louann Salt has no index fossils and the age is based on the ages of formations below and above. Salt deposition began in the Jurassic after the first rotation of the Yucatan