Rock River (Big Sioux River tributary)

The Rock River is a tributary of the Big Sioux River, about 144 mi long, in southwestern Minnesota and northwestern Iowa in the United States. Via the Big Sioux and Missouri rivers, it is part of the watershed of the Mississippi River. The river's name comes from a prominent rocky outcrop about 175 feet high (designated "The Rock" on Joseph Nicollet's 1843 map of the area) of reddish-gray Sioux Quartzite, about 3 miles (5 km) north of Luverne. The outcrop of quartzite is contained in Minnesota's Blue Mounds State Park.

Course
The Rock River starts in Pipestone County, Minnesota, approximately 13 mi northeast of the town of Pipestone, and flows initially southwardly through Rock County, Minnesota, and Lyon County, Iowa, where it turns southwestward into Sioux County, Iowa. It flows into the Big Sioux River in Sioux County, 6 mi north of Hawarden.

Along its course the Rock River passes the towns of Holland, Edgerton, Luverne and Ash Creek in Minnesota; and the towns of Rock Rapids, Doon and Rock Valley in Iowa.

Tributaries
In its upper course in Minnesota, the river collects the East Branch Rock River, about 15 mi long, which flows for its entire length in Pipestone County. In Iowa, it collects the Little Rock River just south of Doon.