The Black Hills is an isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States.

It formed as a result of an upwarping of ancient rock, after which the removal of the higher portions of the mountain mass by stream erosion produced the present-day topography.

In 1868, the federal US government signed the Fort Laramie Treaty of 1868, establishing the Great Sioux Reservation west of the Missouri River, and exempting the Black Hills from all non-indigenous settlement “forever”; however, when American settlers discovered gold here as a result of George Armstrong Custer's Black Hills Expedition in 1874, a gold rush swept in miners.

The US government conquered the Black Hills and forcibly relocated the Lakota, following the Great Sioux War of 1876, to five smaller reservations in western South Dakota, selling off 9 million acres (36,000 km2) of their former land.

[10] As the economy of the Black Hills has shifted away from natural resources (mining and timber) since the late 20th century, the hospitality and tourism industries have grown to take its place.

The Southern Hills is home to Mount Rushmore National Memorial, Wind Cave National Park, Jewel Cave National Monument, Black Elk Peak (the highest point in the United States east of the Rockies), Custer State Park (the largest state park in South Dakota), the Crazy Horse Memorial, and The Mammoth Site in Hot Springs, the world's largest mammoth research facility.

Attractions in the Northern Hills include Spearfish Canyon, historic Deadwood, and the Sturgis Motorcycle Rally, held each August.

Scientists have been able to utilize carbon-dating to evaluate the age of tools found in the area, which indicate a human presence that dates as far back as 11,500 BC with the Clovis culture.

The Lakota (also known as Sioux) arrived from Minnesota in the 18th century and displaced the other tribes that lived there, who eventually moved to what became known as the Western United States.

In order to secure safe passage of settlers on the Oregon Trail, and to end intertribal warfare, the United States government proposed the Fort Laramie Treaty of 1868, which established the Great Sioux Reservation west of the Missouri River and acknowledged indigenous control of the Black Hills.

Both the Sioux and Cheyenne also claimed rights to the land, saying that their cultures considered it the axis mundi, or sacred center of the world.

During the 1875–1878 gold rush thousands of miners went to the Black Hills; in 1880, the area was the most densely populated part of the Dakota Territory.

Following the defeat of the Lakota and their Cheyenne and Arapaho allies in 1876, the United States occupied the Black Hills in disregard of past treaties.

Anaya met with tribes in seven states on reservations and in urban areas as well as with members of the Obama administration and the Senate Committee on Indian Affairs.

In an appeal issued August 21, 2012, Anaya brought a sale of over 1,900 acres of land in Black Hills by the Reynolds family to the attention of the US government and asked that it disclose measures taken by federal or state governments to address Sioux concerns over the sale of the land within Reynolds Prairie.

[21] After 2,022 acres of Pe' Sla (Reynolds Prairie) were granted Federal Indian trust status by the Bureau of Indian Affairs in March 2016, the Shakopee Mdewakanton tribe released a statement acknowledging the 2012 land purchase of 1,940 acres of Pe' Sla and also stated that this purchase was the result of a joint effort by the Rosebud, Shakopee Mdewakanton, Crow Creek, and Standing Rock Sioux Tribes.

[22] In March 2017, Pennington County agreed to abandon its claim to the Pe' Sla area and recognize its Federal Indian trust status.

The stratigraphy of the Black Hills is laid out like a target, as it is an oval dome, with rings of different rock types dipping away from the center.

This collision, called the Trans-Hudson Orogeny, caused the original rocks to fold and twist into a vast mountain range.

Today we see the evidence of this erosion in the Black Hills, where the metamorphic rocks end in an angular unconformity below the younger sedimentary layers.

Above this, the layers of rocks are less distinct and are all mainly grey shale with three exceptions: the Newcastle sandstone; the Greenhorn limestone, which contains many shark teeth fossils; and the Niobrara Formation, which is composed mainly of chalk.

Oddly, this endemic variety of spruce does not occur in the moist Bear Lodge Mountains, which make up most of the Wyoming portion of the Black Hills.

Biologically, the Black Hills is a meeting and mixing place, with species common to regions to the east, west, north, and south.

The southern Black Hills are in Custer and Fall River Counties and are administered in the national forest's Hell Canyon District.

Finally, Wyoming's Black Hills follow the Bearlodge District, approximately Weston and Crook Counties.

Geologically separate from the Black Hills are the Elk Mountains, a small range forming the southwest portion of the region.

The George S. Mickelson Trail is a recently opened multi-use path through the Black Hills that follows the abandoned track of the historic railroad route from Edgemont to Deadwood.