Rock Creek is a 52-mile river in Missoula and Granite County, Montana. Rock Creek is a tributary of the Clark Fork river. The river's headwaters are in Lolo National Forest near Phillipsburg, Montana. The river roughly parallels the Sapphire Mountains and enters the Clark Fork of the Columbia River near Clinton, Montana. Sapphires are found along th…Rock Creek is a 52-mile river in Missoula and Granite County, Montana. Rock Creek is a tributary of the Clark Fork river. The river's headwaters are in Lolo National Forest near Phillipsburg, Montana. The river roughly parallels the Sapphire Mountains and enters the Clark Fork of the Columbia River near Clinton, Montana. Sapphires are found along the river.