Page 2 The 1990 U.S. Census Bureau population data indicate that approximately 4,166,000 people lived in counties that are wholly or partly within the study unit. Most of the population resides in and near Pittsburgh, an urban-suburban area. The 1990 population density within a 10-mile radius of Pittsburgh commonly exceeds 5,000 people per square mile, and the population density is greater than 13,000 people per square mile in parts of Pittsburgh. Areas distant from Pittsburgh are generally rural and the 1990 population density is less than 130 people per square mile except for towns such as Johnstown, Jamestown, Morgantown, and other towns near major transportation corridors. Major industries include manufacturing, coal mining, oil and gas production, construction industry, transportation industries, forestry, agriculture, and outdoor recreation.
Forests are the dominant land use.
The remaining 1 percent of the area was covered by streams, lakes, and wetlands. The Allegheny River begins in northern Pennsylvania, flows north into New York, then bends to the south to flow again through Pennsylvania toward Pittsburgh. Major tributaries of the Allegheny River include the Conewango Creek, French Creek, Clarion River, Redbank Creek, Kiskiminetas River, and Cone-maugh River. Mean annual flow of the Allegheny River 24 river miles upstream from the Ohio River is 19,660 cubic feet per second. The Monongahela River begins in West Virginia at the confluence of the West Fork River and Tygart Valley River and flows northward to Pittsburgh.