The areas where rivers and streams drop from a high elevation to coastal plains, historically popular sites to establish cities, are called fall lines.
Explanation:
A fall line is generally formed at the stratigraphic interface between a crystalline basement of orogenic origin and sedimentary deposits of maritime origin. This bordering zone, which can be ten kilometers wide, corresponds in fact to an ancient shore line of an ocean. This strip of land in the form of a belt is formed under the action of differential erosion by the elements and the rivers. The resulting geomorphology is mainly due to the difference in hardness between the hard crystalline basement and the softer sedimentary layers. Thus the rivers arriving at the level of the stratigraphic interface deeply dig the sedimentary layers resulting in the formation of waterfall at this level.
