The Delgado Mine was a mine located next to the Boot Hill Cemetery. It was where Doc Brown, who was unable to fix the badly damaged DeLorean time machine due to lack of suitable replacement parts in 1885, hid the car for seventy years. Doc sent a letter to Marty in 1955 via several generations of Western Union to inform him of this, and also put an envelope containing repair instructions and a schematic diagram in the DeLorean to enable Marty and his younger self to restore it to working order using 1955 components to replace the burnt-out time circuit control microchip.