Before the Ice Age, approximately one million years ago, the Allegheny River was three distinct and unrelated rivers. The "Lower" Allegheny followed the course of the Clarion to Pittsburgh, where it met the north-flowing Monongahela that drained into the ancestral Erie Basin. The "Middle" Allegheny started northeast of Tidioute, went down to Franklin, then flowed north up present-day French Creek. The "Upper" Allegheny flowed from Potter County through Olean, NY, through Chautauqua County and emptied into the Erie Basin. The illustration to the right is the artist’s rendering of the land, rivers, and events that took place in the northwest part of the Watershed 10,000 years ago and more.