The Cheyenne 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 the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

s of Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 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...

. It is approximately 295 mi (475 km) long and drains an area of 24240 mi2

Formed by the confluence of Antelope and Dry Fork creeks, it rises in northeastern Wyoming in the Thunder Basin National Grassland

Thunder Basin National Grassland

The Thunder Basin National Grassland is located in northeastern Wyoming in the Powder River Basin between the Big Horn Mountains and the Black Hills. The Grassland ranges in elevation from feet to and the climate is semi-arid. The Grassland provides opportunities for recreation, including hiking,...

 in northeastern Converse County. It flows east into South Dakota, passes Edgemont

Edgemont, South Dakota

Edgemont is a city in Fall River County, South Dakota, United States. The population was 774 at the 2010 census.-Geography:Edgemont is located at ....

, and skirts the southern end of the Black Hills

Black Hills

The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is something of a geological anomaly—accurately described as an "island of...

, passing through Angostura Reservoir

Angostura Reservoir

Angostura Reservoir is a reservoir on the Cheyenne River in Fall River County, South Dakota, USA. It was created after the construction of Angostura Dam in 1949 for irrigation...

.

On the east side of the Black Hills, it flows northeast, past Oral

Oral, South Dakota

Oral is an unincorporated community in Fall River County, South Dakota, United States at an elevation of . Although not tracked by the Census Bureau, Oral has been assigned the ZIP Code of 57766.-External links:*...

 and the Buffalo Gap National Grassland

Buffalo Gap National Grassland

Buffalo Gap National Grassland is a National Grassland located primarily in southwestern South Dakota, United States. It is also the second largest National Grassland. Characteristics of the grasslands include mixed prairie and chalky badlands. The grassland is managed by the U.S. Forest Service...

, and along the northwestern boundary of the Pine Ridge Indian Reservation

Pine Ridge Indian Reservation

The Pine Ridge Indian Reservation is an Oglala Sioux Native American reservation located in the U.S. state of South Dakota. Originally included within the territory of the Great Sioux Reservation, Pine Ridge was established in 1889 in the southwest corner of South Dakota on the Nebraska border...

 and Badlands National Park

Badlands National Park

Badlands National Park, in southwest South Dakota, United States preserves of sharply eroded buttes, pinnacles, and spires blended with the largest protected mixed grass prairie in the United States....

.