From the Rocky Mountains of southwestern Montana, three small rivers converge to form the headwaters of the Jefferson River. The longest begins at Brower's Spring, 9,030 feet (2,750 m) above sea level, on the northern flank of the Centennial Mountains. The site is marked by a pile of rocks. The water flows west then north as Hell Roaring Creek before merging with Rock Creek and flowing west through Upper and Lower Red Rock Lakes. Here it becomes the Red Rock River, flowing west through Lima Reservoir and then northwest into Clark Canyon Reservoir near Dillon. Below the dam, the river is known as the Beaverhead River. It is joined by the Ruby River above the town of Twin Bridges and converges with the Big Hole River to form the Jefferson about two miles downstream from town.