The highest headwaters begin along the slopes of Mount Data in the Cordillera mountains at Bauko, Mountain Province. It then flows northeastward through Bontoc, Sabangan, Sadanga, Tinglayan, Lubuagan, Tabuk City, Pinukpuk, Tuao, Piat, Rizal, and finally at Santo Niño, where it merges with the Cagayan River.