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 the present Gulf of Mexico basin originated in Late Triassic time as the result of rifting within Pangea. The rifting was associated with zones of weakness within Pangea, including sutures where the Laurentia, South American, and African plates collided to create it. First, there was a Late Triassic-Early Jurassic phase of rifting during which rift valleys formed and filled with continental red beds. Second, as rifting progressed through Early and Middle Jurassic time, continental crust was stretched and thinned. This thinning created a broad zone of transitional crust, which displays modest and uneven thinning with block faulting, and a broad