A coastal plain is a flat, low-lying piece of land next to the ocean. Coastal plains are separated from the rest of the interior by nearby landforms, such as mountains.

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 coastal plain that formed when the Western Interior Seaway was forced to the Gulf of Mexico about 100 million years ago. The Western Interior Seaway was a large sea that split the continent of North America from what is now the Gulf of Mexico to the Arctic Ocean during the Cretaceous period.

A coastal plain can also develop when river currents carry rock, soil and other sedimentary material into the ocean. Layers of this deposited sediment build up over time, creating a flat or gently sloping landscape.

coastal plain
Wetlands often dominate coastal plains.

Coastal Strawberries
The Oxnard Plain, a coastal plain in southern California, is home to some of the most fertile soil in the world. Some of the world's juiciest strawberries are grown there.

adjacent
Adjective

next to.

Noun

edge of land along the sea or other large body of water.

Noun

low, flat land lying next to the ocean.

Noun

part of a continent that extends underwater to the deep-ocean floor.

Cretaceous period
Noun

145 million to 65 million years ago. The period ended with extinction of the dinosaurs and the rise of mammals.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

geologic
Adjective

having to do with the physical formations of the Earth.

interior
Noun

internal or inland.

mountain
Noun

landmass that forms as tectonic plates interact with each other.

Noun

large body of salt water that covers most of the Earth.

Noun

movement and interaction of the Earth's plates.

rock
Noun

natural substance composed of solid mineral matter.

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

Noun

solid material transported and deposited by water, ice, and wind.

soil
Noun

top layer of the Earth's surface where plants can grow.

Western Interior Sea
Noun

large, inland sea that split the continent of what is now North America into two parts during most of the early and late Cretaceous period. Also called the Cretaceous Seaway, the Niobrara Sea, and the North American Inland Sea.