Copper was essential to America’s Industrial Revolution, the Age of Electricity, and the Information Revolution because it is a superb conductor used in house wiring, cars, and electronic devices. Underground mining first targeted high-grade ore, but as copper demand rose through the 20th century and new technologies made it profitable to extract copper from low-grade ore, open-pit mining turned to the low-grade ore in hills around the underground mines and maximized copper recovery. Waste rock containing little or no copper was piled into man-made hills called stockpiles, and even tiny traces of copper can now be extracted from these piles through leaching. Rising demand accompanied developments such as the Model T, air conditioning, U.S. entry into World War I, World War II, and the Korean conflict, while falling demand came with the 1929 stock market crash and the 1974 and 2008 recessions. Blasting began on the Sacramento Pit in 1917, production began there in 1921, and operations ceased in 1929; development of the Lavender Pit began in 1950, production began in 1954, and operations ceased in 1974. By the mid-1970s, Bisbee’s mines had run out of desirable ore and shut down, but mining could begin again if copper demand and prices rise enough and improved technology makes extraction of the very low-grade copper in Bisbee’s hills profitable.