Plain, an extensive area of flat or gently rolling land. Most plains are of low elevation, but some, such as the Great Plains of the western United States, slope gradually upward to higher altitudes and are called high plains.
Many of the world's plains were formed by rivers and glaciers. A river deposits materials in its valley and at its mouth to form floodplainsand delta plains.Melting glaciers form outwash plainsand till plains. Lacustrine plainsare dry lake beds. Wind-blown silt, deposited over centuries, forms loess plainsin large areas of China and parts of the United States. Abyssal plainscovered with marine deposits lie at great depths on the ocean floor. Coastal plainsare low, flat areas along seacoasts.
Plains do not have a specific type of vegetation. Some, such as the Everglades of Florida, are grassy swamps. Others are barren deserts. The tundrais a treeless plain found in arctic regions. Some plains are covered with dense forests. Plains with natural vegetation of grasses and scattered trees include the prairiesof North America and the pampas, llanos, and camposof South America.
The most extensive plains in the United States are the Great Plains, extending from western Texas north to Canada; the Central Lowlands, from Oklahoma northeast to Ohio; and the Coastal Plain, from Texas to New York.
