This is the term given to a geologic break between and upland region and a coastal plain, and is often crossed by a river with varying degrees of rapids.

A geologic break between an upland region and a coastal plain is called a fall line. It can denote the frequent change between upland harder, crystalline rock and softer often sedimentary flat lying rocks. The rugged  Fraser Canyon in BC, Canada which passes through partly volcanic and granitic rocks is an example of such an upland region and where the Fraser River flows out onto the coastal plain of in part the Lower Mainland the plain is underlain by the softer sandstones and shales of the Huntingdon Formation.