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 Mexico which penetrated the Late-Triassic and Early-Jurassic strata, filling the extensional graben features. The Gulf of Mexico basin red beds are specifically named the Eagle Mills formation, located directly beneath the salt, evaporite and marine sediments deposited during the Jurassic, and often found with the diabase dikes and basalt flows mentioned above. Basement rocks in the northeastern region of the Gulf of Mexico basin are fragments of the African plate which remained behind during the breakup of Pangaea and date back to the late Precambrian through the Cambrian. It is atop these Precambrian plate fragments that the mainly carbonate and