In the late 18th century, the Butte Copper Mines were the leading source of copper in the world. One hundred years earlier, Butte began as a silver and gold mine, but as the American Industrial Revolution rapidly swept across the country, and the demand for and use of electricity skyrocketed, the volume of copper being pulled from the mines increased exponentially. Butte flourished. Though, with the sheer number of active mines and the thousands of worker there within, of course accidents are bound to happen. On June 8, 1917, the deadliest recorded underground mining accident occurred in the Speculator Mine, when a fire erupted and spread throughout the shaft, asphyxiating 168 men. A memorial now stands commemoration of these lives lost on the northeastern ridge of the Berkeley Pit. The Berkeley Pit was opened in 1955 as the mine transitioned from operating primarily underground to primarily above ground, which was more cost and labor efficient. This “open pit mine”, the Berkeley Pit, would produce over 290 million tons of copper before operations ended in 1982, earning the mine the nickname, “The Richest Hill on Earth.”