On this date, April 29, 1868, a number of Lakota tribes and the Arapaho signed the Treaty of Fort Laramie, which recognized the Black Hills as part of the Great Sioux Reservation.  The rest, as the say, his history. 

Source: http://www.historicaldocuments.com/TreatyofFortLaramielg.htm

Historical Documents
Treaty of Fort Laramie

In this treaty, signed on April 29, 1868, between the U.S. Government and the Sioux Nation, the United States recognized the Black Hills as part of the Great Sioux Reservation, set aside for exclusive use by the Sioux people.

Source: http://puffin.creighton.edu/lakota/1868_la.html

FORT LARAMIE TREATY APRIL 29, 1868

TREATY WITH THE SIOUX-- BRULÉ, OGLALA, MINICONJOU, YANKTONAI, HUNKPAPA, BLACKFEET, CUTHEAD, TWO KETTLE, SANS ARCS, AND SANTEE--AND ARAPAHO

15 Stat., 635.
Ratified, Feb. 16, 1869.
Proclaimed, Feb. 24, 1869

Articles of a treaty made and concluded by and between Lieutenant-General William T. Sherman, General William S. Harney, General Alfred H. Terry, General C. C,. Augur, J. B. Henderson, Nathaniel G. Taylor, John B. Sanborn, and Samuel F. Tappan, duly appointed commissioners on the part of the United States, and the different bands of the Sioux Nation of Indians, by their chiefs and head-men, whose names are hereto subscribed, they being duly authorized to act in the premises.

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On this date, April 20, 1992, a major blizzard that hit the Black Hills, dumping nearly three feet of snow in some areas and packing 60+ mph winds ended. 

Source: http://www.crh.noaa.gov/fsd/?n=fsdtrivia04

A blizzard beginning on April 18th, 1992 lasted into the 20th across the Black Hills of South Dakota. Heavy wet snow and strong winds created blizzard conditions in the northern Black Hills that led to a major power outage. About 2000 households were without power for over 4 hours in some areas around Lead/Deadwood. Snow amounts of 2 feet were common with 30 inches falling at Lead causing major traffic problems. Northwest winds gusted to over 65 miles an hour at Rapid City and to around 50 mph in the Hills .

(Sorry for the multiple posting. It's been a busy week.)

April 3

On this date, April 3, 1936, the coldest temperature ever recorded during the month of April at Sioux Falls occurred, when the temperature fell to just 4 degrees F above zero.

Source:   http://www.crh.noaa.gov/fsd/?n=fsdtrivia04

April 4

On this date, April 4, 1881, 40,000 cattle were represented by the Black Hills Stockgrower's Association.

Source: http://www.southdakotastockgrowers.org/history.htm

April 5

On this date, April 5, 1862, the Territorial Legislature passed an act establishing Lincoln, Minnehaha, Brookings, and Deuel Counties.

Source: Minnehaha County History, p. 19.

On this date, March 12, 1954, a major blizzard hit the Black Hills.

Source: http://www.intellicast.com/Almanac/NorthernPlains/March/

March 12, 1954 -

a blizzard raged from eastern Wyoming into the Black Hills of western South Dakota while a severe ice storm was in progress from northeastern Nebraska to central Iowa . The ice storm isolated 153 towns in Iowa . Dust from the Great Plains caused brown snow, while hail and muddy rain fell over parts of Wisconsin and Michigan

Feds to the Lakota: "You don't sell the Black Hills, we declare you hostile."On this date, January 31, 1876, the federal government decreed that all Lakota not on a reservation were considered hostile.  The Lakota had rebuffed the government's attempt to purchase the Black Hills.

Source: http://www.pbs.org/weta/thewest/people/s_z/sittingbull.htm

When government efforts to purchase the Black Hills failed, the Fort Laramie Treaty was set aside and the commissioner of Indian Affairs decreed that all Lakota not settled on reservations by January 31, 1876, would be considered hostile. Sitting Bull and his people held their ground.

On this date, January 19, 1982, the U.S. Supreme Court decided to not hear an appeal regarding the return of lands in the Black Hills to the Oglala Sioux Tribe and other Indian nations. 

Source: http://query.nytimes.com/gst/fullpage.html?res=9405E2D81138F93AA25752C0A964948260&n=Top%2fNews%2fNational%2fU%2eS%2e%20States%2c%20Territories%20and%20Possessions%2fSouth%20Dakota

SIOUX LOSE FIGHT FOR LAND IN DAKOTA

By LINDA GREENHOUSE, SPECIAL TO THE NEW YORK TIMES
The decades-long effort in Federal courts by a tribe of Sioux seeking to regain ownership of the Black Hills of South Dakota ended today when the Supreme Court refused to hear an appeal. A lawyer for the tribe, the Oglala Sioux of the Pine Ridge Reservation, said that the efforts would now shift to the United Nations. The end came when the Justices, without comment, refused to hear an appeal from a lower court ruling that limited the Indians to cash compensation rather than the land itself. The tribe's lawyer, Russel Barsh, said that stress would now be placed on the United Nations, where, since 1980, the Human Rights Commission has been investigating a charge by the Sioux that the Federal Government's handling of the Indians' claim to the Black Hills violates international law.