Monongahela

Geography

The Monongahela is formed by the confluence of the West Fork River and its "east fork"—the Tygart Valley River—at Fairmont in north central West Virginia. From there it flows northeasterly to cross the Pennsylvania border just west of north Cheat Lake on its Cheat River tributary. Then it flows northerly across southwestern Pennsylvania, taking a bit of a detour northeast 10 miles south of Pittsburgh to approach Pittsburgh from the southeast and its confluence with the Allegheny River to form the Forks of the Ohio at "The Point" of Point State Park in Downtown Pittsburgh.

History

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. 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.

Geology

Prior to early Pleistocene regional glaciation, more than 780,000 years ago, the ancestral Monongahela River (a.k.a. the Pittsburgh River) flowed northward from present-day north-central West Virginia, across western Pennsylvania and northwestern Ohio, and into the Saint Lawrence River watershed. 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. A river-lake with many narrow bays, its maximum water surface rose to 1,100 feet (340 m) above sea level.