The North Platte rises in the high basin of North Park located in north-central Colorado, near the town of Walden, on the eastern slope of the Park Range. It flows northward into Wyoming (through Northgate Canyon), along the western side of the Medicine Bow Mountains. On the north end of the range it is joined by the Medicine Bow River in the Seminoe Reservoir, then downstream of the Kortes Reservoir it is joined by the Sweetwater River in the Pathfinder Reservoir. Northeast of the reservoir it passes through the Alcova and Gray Reef Reservoirs and flows northeast between the Granite Mountains to the west and the Laramie Mountains to the east.