The Grand River is a tributary of the Missouri River

Missouri River

The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...

 in North Dakota

North Dakota

North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....

 and South Dakota

South Dakota

South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The length of the combined branch is 110 mi (177 km). With its longest fork, its length is approximately 200 mi (320 km).

It is formed by the confluence of the North Fork

North Fork Grand River (South Dakota)

The North Fork of the Grand River is a tributary of the Grand River, approximately 80 mi long, in North Dakota and South Dakota in the United States....

 (which rises in North Dakota) and the longer South Fork

South Fork Grand River (South Dakota)

The South Fork of the Grand River is a tributary of the Grand River, approximately 90 mi long, in South Dakota in the United States....

 (which rises in South Dakota) in northwestern South Dakota near Shadehill in Perkins County

Perkins County, South Dakota

As of the census of 2000, there were 3,363 people, 1,429 households, and 937 families residing in the county. The population density was 1.2 people per square mile . There were 1,854 housing units at an average density of 0.6 per square mile...

, near several parcels of the Grand River National Grassland

Grand River National Grassland

Grand River National Grassland is a National Grassland in northwestern South Dakota, USA. It is named for the Grand River. The North and South forks of the rivers meet in the grassland. It has a land area of 154,783 acres . In descending order of acreage it lies in parts of Perkins, Corson, and...

. It flows east, through the Standing Rock Indian Reservation

Standing Rock Indian Reservation

The Standing Rock Indian Reservation is a Lakota, Yanktonai and Dakota Indian reservation in North Dakota and South Dakota in the United States...

  and joins the Missouri in Lake Oahe

Lake Oahe

Lake Oahe is a large reservoir behind Oahe Dam on the Missouri River beginning in central South Dakota and continuing north into North Dakota in the United States. The lake has an area of and a maximum depth of . By volume, it is the fourth-largest reservoir in the US. Lake Oahe has a length of...

, approximately 10 mi (16 km) northwest of Mobridge

Mobridge, South Dakota

Mobridge is a city in Walworth County, South Dakota, United States. The population was 3,465 at the 2010 census.-Geography:Mobridge is located at ....

. The lower 15 mi (25 km) of the river form an arm of the Lake Oahe reservoir.

The forks of the Grand was the site of the famous 1823 attack by a grizzly bear

Brown Bear

The brown bear is a large bear distributed across much of northern Eurasia and North America. It can weigh from and its largest subspecies, the Kodiak Bear, rivals the polar bear as the largest member of the bear family and as the largest land-based predator.There are several recognized...

 on frontiersman Hugh Glass

Hugh Glass

Hugh Glass was an American fur trapper and frontiersman noted for his exploits in the American West during the first third of the 19th century....

.