The largest American river east of the Appalachians, the main (North) fork of the Susquehanna rises from Otsego Lake at Cooperstown, New York. Flowing southward and then southwestward, the river and its tributaries drain much of south-central New York; after passing through Binghamton, the Susquehanna makes a broad curve to the west before passing through Wilkes-Barre, Pennsylvania. From that city, it flows southwestward to Northumberland, where it receives its West Fork.
The West Fork of the Susquehanna rises on the Appalachian Plateau, west of Altoona, Pennsylvania. Flowing northward and then eastward, the river drops to the Ridge and Valley Province at Lock Haven and then passes through Williamsport, the largest city along its course; from there, the Susquehanna flows southeastward to its junction with the North Fork.
From Sunbury, Pennsylvania, the combined flow of the Susquehanna angles SSW to Harrisburg and then southeastward to the northern tip of Chesapeake Bay. In fact, the Bay is the drowned valley of the lower Susquehanna and its tributaries; before the last Pleistocene Ice Sheets melted back into Canada, the Susquehanna River flowed another 200 miles to the Atlantic. While its current length is listed as 464 miles (from Otsego Lake to Chesapeake Bay), the river once flowed for 664 miles to the sea, draining half of Pennsylvania along the way.