fall line

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the geographical line indicating the beginning of a plateau, usually marked by many waterfalls and rapids
Skiing the line of direct descent down a hill

the line east of the Appalachian Mountains, marking the end of the coastal plains and the beginning of the Piedmont Plateau

See fall line in American Heritage Dictionary 4

noun

A line connecting the waterfalls of nearly parallel rivers that marks a drop in land level.
The natural line of descent, as for skiing, between two points on a slope.

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fall line science

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