The river rises in the northeastern corner of Pittsburg, New Hampshire, at the outlet of Boundary Pond, whose western end just touches the Canada–United States border. The river flows in a curving route to the east, entering Maine after two miles. The river passes through a wide, wet valley known as Moose Bog, then joins the Second East Branch of the Magalloway River. The juncture of the West Branch and the Second East Branch forms the beginning of the Magalloway.[2]
