It was the Black Hills Gold Rush.

it was caused by gold mines.

Gold was discovered in the Black Hills of South Dakota by a small group of miners led by George Armstrong Custer in 1874. This discovery led to the Black Hills Gold Rush, and the subsequent influx of settlers and miners to the area.

South Dakota has three major attractions. In western South Dakota, there are the Black Hills, which were the site of a major gold rush. In the Black Hills are Mount Rushmore and the Badlands.

Black hills gold is jewellery that was first created in the 1870s during the black gold rush by a French goldsmith. It's made with pure 24 karat gold bars and stocks of pure silver and copper. The prices vary but a woman's gold ring costs between $100 and $600.