Bisbee, in the Mule Mountains of southeastern Arizona, has an extensive mining history dating from the 1870s. It is said the value of copper produced from the Copper Queen in 1925 alone was valued 10 times more than the cost of the Gadsden Purchase, which was $10 million in 1854.
The first open pit mine at Bisbee was the Sacramento pit comprising 35 acres. It began as a shaft in 1911 and six years later developed as an open pit.
Extensive geological research had determined copper ore deposits throughout the Bisbee district resulting from a large mass of intrusive granite porphyry pushed up into the surrounding schist and limestone. The copper was deposited in limestone traps forming ore bodies. Over time, progressive layers of barren limestone were formed on top, with the entire mass tilting southeastward.
Sacramento Hill, a large block of intrusive granite porphyry, contained around 1.48% copper ore per ton while richer ore bodies were found at greater depths further southeast.
Phelps Dodge invested in a large concentrator to mine the 550-foot high Sacramento Hill, which within a few years was reduced to a pit. Rail proved vital in the removal of ore, with the delivery of empty ore cars transported by locomotive along the spiral tracks to the base of the pit to be filled by steam shovels and taken back to the surface for the ore’s treatment at the mill.