More than 100 years old the Hardtack Mine tunnel was made by the employees of the Hidden Treasure Mine Co. It was supposed to be an underground transport tunnel for the Hidden Treasure's ore production located more than a quarter mile up the mountain. Mining accidents along with dwindling financial woes halted the work in 1907 and the connection was never completed.
Treasure City or Treasureville as it was to become known was a collection of shacks and buildings in and around the Hidden Treasure and Hardtack Mines. A bustling little community from the 1890's until 1930, the mine produced more than a million and a half dollars in silver ore. The present location had a mill, mine offices, a bank, boarding houses, and a commissary. One mile up the road at the Ute - Ulay Lake City Mines was a one room schoolhouse for the miners children.
With the decline of metal ore production, especially silver in the 1930's the curtailment and existence of the Hidden Treasure Mine and Treasureville was inevitable. Another part of the Hinsdale County Galena Mining District was gone.