Fall line

[1] A fall line often will recede upstream as a river cuts out the uphill dense material, forming "c"-shaped waterfalls and exposing bedrock shoals.

Because of these features, riverboats typically cannot travel any farther inland without portaging, unless locks are built.

Seeking a head of navigation with a ready supply of water power, people have long made settlements where rivers cross a fall line.

As such, many cities along a fall line grew as a result of demand for transferring people and goods between land-based and water-based transportation at that place.

The fall line marks the geologic boundary of hard metamorphosed terrain—- the product of the Taconic orogeny—- and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated Cretaceous and Tertiary sediments.