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 center active contemporaneously in regards to geologic time. The transform boundary caused two approximately 22° counterclockwise rotations of the Yucatan Block away from the North American plate. One rotation happened prior to seafloor spreading, and the second rotation happened while the basin spread, creating the current geographical shape of the Gulf of Mexico and the current placement of the Yucatan Peninsula. The active rifting of the Late-Triassic to Mid-Jurassic, and the stratigraphy which depended strongly on that tectonic development, is followed by a relatively calm tectonic period in the Late-Jurassic. The Late-Jurassic Gulf of Mexico is characterized mostly by prolonged