Flash flood hits Rapid City - Jun 09, 1972 - HISTORY.com

A flash flood in Rapid City, South Dakota, kills more than 200 people on this day in 1972. This flood demonstrated the danger of building homes and businesses in a floodplain region.

The native Sioux called the river Minnelusa when European settlers overtook the Black Hills region in 1876 as part of one of the last gold rushes in North American history. The settlers built the town of Rapid City well south of the floodplain and for 75 years there were few flooding problems for the residents.

In 1952, the Pactola Dam was built 10 miles from the city. The new dam controlled the floods, setting off a boom in development of the floodplain area. Eventually, the Rapid City area became home to 50,000 people.

In the spring of 1972, torrential rains battered the Black Hills. Warm moist air from the Gulf of Mexico collided with a Canadian cold front, causing 15 inches of rain to come down in only six hours. The spillway for the Pactola Dam got clogged with debris during the storm, leading to the total collapse of the dam and a devastating wave of water crushed most of the nearby buildings and swept away 238 people. Residents, most of whom were not insured for flood damage, suffered $160 million in damages.

In the wake of this tragedy, it was decided that the floodplain should no longer be used as a residential area. It is now a golf course and a park with several ponds.