A basic fact about coastal plains that kids should know is that coastal plains are flat, low-lying pieces of land next to an ocean or a sea coast. One of the largest coastal plains in the world is in eastern South America.
Coastal plains in the United States are found along the Gulf of Mexico and the Atlantic Ocean. Coastal plains feature a body of water, such as an ocean, on one side and a landform, such as a mountain or hills, on the other. The inland boundary of a coastal plain is called a fall line.
Coastal plains may form as continental shelves or when sedimentary material in the ocean builds up to create a flat landscape. A continental shelf is a flat piece of land located just below sea level. It forms a coastal plain when the ocean level drops and exposes the flat piece of land. Such coastal plains can extend very far inland.
Coastal plains also develop when river currents carry soil, rocks and other sedimentary materials into the ocean. After a while, the sedimentary materials build up to create a gently sloping or flat landscape just above sea level. Wetlands often dominate coastal plains, and this creates an important ecosystem for several species.