South Dakota is a state located in the north-central United States. It is usually considered to be in the Midwestern region of the country. The state can generally be divided into three geographic regions: eastern South Dakota, western South Dakota, and the Black Hills. Eastern South Dakota is lower in elevation and higher in precipitation than the western part of the state, and the Black Hills are a low, isolated mountain group in the southwestern corner of the state. Smaller sub-regions in the state include the Coteau des Prairies, Missouri Coteau, James River Valley, and the Dissected Till Plains. Geologic formations in South Dakota range in age from two billion-year-old Precambrian granite in the Black Hills to glacial till deposited over the last few million years. South Dakota is the 17th-largest state in the country.
South Dakota has a humid continental climate in the east and the Black Hills, and a semi-arid climate in the west outside of the Black Hills, featuring four very distinct seasons, and the ecology of the state features plant and animal species typical of a North American temperate grassland biome. A number of areas under the protection of the federal or state government, such as Badlands National Park, Wind Cave National Park, and Custer State Park, are located in the state.
In 2025, the population of South Dakota was estimated to be 924,669, and the state ranks fifth-lowest in both total population as well as population density in the United States. Sioux Falls, with a population of just over 200,000 is the largest city in the state. Rapid City ranks as South Dakota's second-largest city, and Pierre is the state capital. Historically a very agricultural state, the service and tourism sectors have grown in economic importance in recent years.
Location and size
South Dakota is situated in the north-central United States, and is considered to be a part of the Midwest by the U.S. Census Bureau,Census Regions and Divisions of the United States, U.S. Census Bureau. Retrieved 2009-01-29. although the Great Plains region also covers the state. Additionally, the culture, economy, and geography of western South Dakota has more in common with the West than the Midwest.Johnson, Dirk. Gold Divides Dakotans as River Did The New York Times. October 9, 1988. (accessed 2008-2-14)Hasselstrom, Linda: Roadside History of South Dakota, pages 2–4. Mountain Press Publishing Company, 1994 The state has a total land area of 77,116 sq. miles (199,905 km2), making it the 17th largest in the Union.
South Dakota is bordered to the north by North Dakota; to the south by Nebraska; to the east by Iowa and Minnesota; and to the west by Wyoming and Montana. The western border is the Black Hills meridian, a north-south line set out at a certain distance from Washington, D.C., to separate South Dakota from Montana and Wyoming during the transition to statehood. The northern border is the 46th parallel north and was originally marked by 720 quartzite monuments over of prairie.
Two time zones cover South Dakota; the state is split roughly in half between the Central Time Zone (UTC-6) in the east and the Mountain Time Zone (UTC-7) in the west. The boundary between the two zones runs south down the Missouri River until Pierre, at which point the boundary roughly continues due south while the river turns southeast.
The North American continental pole of inaccessibility is in Bennett County, located 1024 mi (1650 km) from the nearest coastline, between Allen and Kyle (Oglala Lakota County) at .
Regions
South Dakota can generally be divided into three regions: eastern South Dakota, western South Dakota, and the Black Hills.Thompson (ed.), p. 14. The Missouri River serves as a somewhat stark boundary in terms of geographic, social and political differences between eastern and western South Dakota, and the geography of the Black Hills differs from its surroundings to such an extent that it can be considered separate from the rest of western South Dakota. South Dakotans also at times combine the Black Hills with the rest of western South Dakota, and refer to the two resulting regions, divided by the Missouri, as West River and East River.
Eastern South Dakota is generally wetter and features lower topography than the western part of the state. Smaller geographic regions of this area include the Coteau des Prairies, the Dissected Till Plains, and the James River Valley. The Coteau des Prairies is a higher region bordered on the east by the Minnesota River Valley and on the west by the James River Basin.Thompson (ed.), pp. 17–18. Numerous glacial lakes cover the Coteau, and it is largely drained by the Big Sioux River, a tributary of the Missouri. Further to the west, the James River Basin is mostly low, flat, highly eroded land, following the flow of the James River through South Dakota from north to south. The Dissected Till Plains, an area of rolling hills and fertile soil that covers much of Iowa and Nebraska, also extends into the southeastern corner of South Dakota.
The Missouri Coteau lies between the James River Basin of the Drift Prairie and the Missouri River.Thompson (ed.), p. 20. This region is the southern section of a large plateau extending into Canada.
The Great Plains cover most of the western two-thirds of South Dakota. West of the Missouri River the landscape becomes more rugged and consists of rolling hills, plains, ravines, and steep flat-topped hills called buttes. These buttes sometimes rise 400 to 600 feet (120 to 180 m) above the plains. In the south, east of the Black Hills, lie the South Dakota Badlands.
The Black Hills are in the southwestern part of South Dakota and extend into Wyoming. This range of low mountains covers 6,000 sq. miles (15,500 km2.) with mountains that rise from 2,000 to 4,000 feet (600 to 1,200 m) above their bases. The highest point in South Dakota, Black Elk Peak (formerly named Harney Peak) is 7,242 ft or 2,207 m above sea level and is in the Black Hills. This is the highest point in the United States east of the Rocky Mountains. Other Black Hills mountains that are over 7,000 ft (2,133 m) in elevation include Bear Mountain, Crooks Tower, Terry Peak, and Crows Nest Peak. The Black Hills are rich in minerals such as gold, silver, copper, and lead. The Homestake Mine, the largest and deepest gold mine in North America, was located in the Black Hills and produced over $1 billion in gold since it started operation in 1876.Yarrow, Andrew L. "Beneath South Dakota's Black Hills", The New York Times, August 9, 1987. Accessed January 11, 2008. "The Homestake Mine, in Lead, has operated continuously since 1876, a year before George Hearst purchased the claim for $77,000. Homestake, which is the largest, deepest and most productive gold mine in North America, has yielded more than $1 billion in gold over the years." The mine is now a scientific laboratory.
Geology
South Dakota geologic formations and deposits range in age from several billion to several thousand years, and the age of the rocks generally decreases as one moves from west to east across the state. The oldest geologic formations in the state were created over two billion years ago during the Precambrian, and consist of metamorphic and igneous rocks. These form the central core of the Black Hills, but they can also be found in two isolated locations in eastern South Dakota near Milbank and Sioux Falls. Formations from the Paleozoic Era form the outer ring of the Black Hills; these were created between roughly 540 and 250 million years ago. This area features rocks such as limestone which were deposited here when the area formed the shoreline of an ancient inland sea.
Outside of the Black Hills, much of western South Dakota features rock formed during the Mesozoic Era, from 250 million to 66 million years ago. At the time, much of western and central South Dakota was again covered by a shallow inland sea. Marine skeletons from this ocean settled to the seafloor and were compacted to form the sedimentary rocks in the area today. During this period, the Black Hills, which had been pushed up to an elevation of around 15,000 feet (4,500 m), lost around 6,000 feet (1,800 m) worth of rock layers due to erosion. Many of these sediments ended up in the same area as the marine deposits from the inland sea, and both contribute to western South Dakota's present-day geological makeup. In several areas in western South Dakota, tertiary deposits may also be found. These were formed between 66 and 2.5 million years ago from eroded mountains to the west. There is also volcanic material deposited here that presumably came from the Yellowstone area. These layers of sedimentary rock are distinctly visible in the multi-colored rocks and cliffs of Badlands National Park.
Layers deposited during the Pleistocene epoch, starting around two million years ago, cover most of eastern South Dakota. These are the youngest rock and sediment layers in the state, and are the product of several successive periods of glaciation which deposited a large amount of rocks and soil, known as till, over the area. The thickness of the glacial till layer ranges between 100 and 900 feet (30 and 270 m). This till is also what makes agriculture more prevalent in eastern South Dakota as it is extremely fertile.
Much of the human history of South Dakota was shaped by its geology. Gold seekers founded most of the larger cities around the Black Hills, and quarrying was an important economic activity in several areas in eastern South Dakota. Mines and quarries in present-day South Dakota produce gold, Sioux quartzite, Milbank granite, sand, gravel, limestone, mica, and uranium. The state also produces a very limited amount of oil and natural gas.
Rivers and lakes
The Missouri River is the largest and longest river in the state. Other major South Dakota rivers include the Cheyenne, the James, the Big Sioux, and the White. Essentially all of South Dakota's rivers are part of the Missouri River Valley. Dams on the Missouri River create four large reservoirs: Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake. Hydroelectricity generated from power plants at the dams provides approximately half of the electricity used by South Dakotans.
The vast majority of South Dakota's natural lakes are located in the eastern half of the state, and most are the product of the most recent ice age. The title of largest natural lake is somewhat disputed; Lake Thompson is larger than Lake Poinsett, but Lake Poinsett has maintained its current size for a much longer period of time. Other major natural lakes include Lake Kampeska, Waubay Lake, Lake Madison, Lake Whitewood, and Lake Herman. Additionally, two large lakes, Big Stone Lake and Lake Traverse, form part of the border between South Dakota and Minnesota. The continental divide separating the drainage basin of Hudson Bay from that of the Gulf of Mexico is situated between these two lakes.
Ecology
Much of South Dakota, with the notable exception of the Black Hills, is dominated by a temperate grasslands biome. Although grasses and crops cover most of this region, deciduous trees such as cottonwoods, elms, and willows are common near rivers and in shelter belts. In open, uncultivated areas of the plains, grasses such as buffalograss, western wheatgrass, switchgrass, big bluestem and little bluestem thrive. Mammals in this area include bison, deer, pronghorn, coyotes, beavers, and prairie dogs, while reptiles include the snapping turtle, the box turtle, and various types of snakes. The prairie rattlesnake is South Dakota's only venomous snake. Rivers and lakes of the grasslands support populations of walleye, carp, pike, and bass, along with other species. The Missouri River also contains the pre-historic paddlefish, and chinook salmon, native to the Pacific Northwest, have been successfully introduced in Lake Oahe.
Tall grass prairies