Butte County, South Dakota: History
=== Prehistory ===
In 1975, plesiosaur fossils dating to the Cretaceous Period (ca. 110 million years ago) were discovered in Butte County. In the 1980s, a 90-million-year-old fossil of a clawless lobster was discovered. A Tyrannosaurus rex skeleton was found in 1981.
The early human history of the Belle Fourche River Valley has been traced to about 3000 BC. The first people of the area were Native Americans who resided on the northwestern plains of North America. The earliest known evidence of human activity in the area dates to the Middle Plains Archaic Period of the Plains Indians (ca. 3000–1500 BC). Traces of tipi rings dating from this period have been found. In 1979 and 1980, archeologists excavated a fortified and previously inhabited site west of Belle Fourche that dated to AD 1000. This site was called the Smiley-Evans Site and had been recorded in 1959. Until 1984, only 47 archaeological sites had been recorded, but after the excavation of the Smiley-Evans Site, several investigations were undertaken. As of 1989, 199 archaeological sites had been discovered in the county.