[15] Monongalia County and the town of Monongah, both in West Virginia, are named for the river, as is the city of Monongahela in Pennsylvania.

Prior to early Pleistocene regional glaciation, more than 780,000 years ago, the ancestral Monongahela River (a.k.a.

One (or more) extensive ice sheet advance dammed the old north-flowing drainage and created a vast lake—known as Lake Monongahela—stretching from an unknown point north of present-day Beaver, Pennsylvania for ~200 miles (320 km) south to Weston, West Virginia.

Over 200 feet (61 m) deep in places, its southwestward overflow gradually incised old drainage divides and contributed to the geological development of the present-day upper Ohio River Valley.

The river is navigable its entire length with a series of locks and dams that maintain a minimum depth of 9 feet (2.7 m) to accommodate coal-laden barges.

Some of the best known specific stream locations for this include: The Monongahela River valley was the site of a famous battle that was one of the first in the French and Indian War—the Braddock Expedition (May–July 1755).

It resulted in a sharp defeat for two thousand British and Colonial forces against those of the French and their Native American allies.

In 1817, the Pennsylvania legislature authorized the Monongahela Navigation Company to build 16 dams with bypass locks to create a river transportation system between Pittsburgh and the area that would later become West Virginia.

[30] Originally planned to run as far south as the Cheat River, the system was extended to Fairmont, and bituminous coal from West Virginia was the chief product transported downstream.

Following the killing of several workers in the course of the strike, anarchist Emma Goldman wrote: "Words had lost their meaning in the face of the innocent blood spilled on the banks of the Monongahela."

[31] Coal barges are a common sight on the river, and the railways which line either side are heavily used by freight.

[citation needed] The river was the site of a famous airplane crash that has become the subject of urban legends and conspiracy theories.