• coastal plain
    Wetlands often dominate coastal plains.

    Photograph by James P. Blair

    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.

    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.

  • Term Part of Speech Definition Encyclopedic Entry
    adjacent Adjective

    next to.

    coast Noun

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

    Encyclopedic Entry: coast
    coastal plain Noun

    low, flat land lying next to the ocean.

    Encyclopedic Entry: coastal plain
    continental shelf Noun

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

    Encyclopedic Entry: continental shelf
    Cretaceous period Noun

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

    current Noun

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

    Encyclopedic Entry: current
    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.

    ocean Noun

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

    Encyclopedic Entry: ocean
    plate tectonics Noun

    movement and interaction of the Earth's plates.

    rock Noun

    natural substance composed of solid mineral matter.

    sea level Noun

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

    Encyclopedic Entry: sea level
    sediment Noun

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

    Encyclopedic Entry: sediment
    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.

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