The mighty meandering Monongahela River. This figure illustrates how the Monongahela River and its major tributaries changed their channels in numerous places over the last few million years. The dark blue represents water in rivers and creeks. Light blue represents the river valleys. Arrows in abandoned meanders indicate the direction of water flow at the time the meanders were occupied by the rivers. Representative cities and towns have been added for reference. At one time, the rivers flowed over a landscape with low rolling hills separated by wide valleys. The old rivers meandered within broad floodplains, perhaps several miles wide (think Mississippi River!). Over time, old meander bends were abandoned and new ones formed. When the Ice Age began about one million years ago, the rivers rapidly began eroding into the landscape. New, straighter channel segments replaced old meanders at places like Morgantown, West Virginia, and Masontown, Belle Vernon, and Perryopolis, Pennsylvania. At the same time, the rivers continued to cut down while maintaining some of their old meanders in places like the bends north of Carmichaels on the Monongahela, south of McKeesport on the Youghiogheny, and south of Point Marion on the Cheat.