In western South America, a large coastal plain lies between the Andes Mountains and the Pacific Ocean. In the United States, coastal plains can be found along the Atlantic Ocean and the Gulf of Mexico.
Coastal plains can form in two basic ways. Some start as a continental shelf, a flat piece of land located below sea level. When the ocean level falls, the land is exposed, creating a coastal plain. Sometimes, these coastal plains can extend far inland. Fossils of marine organisms have been found in the landlocked U.S. state of Kansas, for instance. Kansas was part of a vast