The New River rises in the Gulf of Slides, a small glacial cirque at the foot of Boott Spur, a southern extension of Mount Washington. Flowing northeast, the stream drops rapidly down the western slopes of Pinkham Notch, joining the Cutler River in the floor of the notch at the Route 16 crossing, just south of the notch's height of land, and just upstream from the Cutler River's merging with the Ellis River.