It flows E, SE, and E away from the mountains, past Simms, Sun River, and Vaughn and joins the Missouri at Great Falls.

The North Fork of the Sun River begins high up in the Bob Marshall Wilderness and flows generally Southward for about 20 miles (32 km) until it meets up with the South Fork of the Sun River.

[9] A sign located 3 miles south of Great Falls gives information on the history of the Sun River:[13] This river was called "The Medicine" by the Indians.

In his journal under that date he said: "when I arrived in sight of the white-bear Islands the missouri bottoms on both sides of the river were crowded with buffaloe I sincerely believe that there were not less than 10 thousand buffaloe within a circle of 2 miles around that place"

The City of Great Falls covers a portion of the plain across which the Expedition made their difficult 18 mile portage around the falls of the Missouri in June 1805