This is an abandoned charcoal oven. These overs are all over the west wherever gold was found and the people who made the charcoal were called “carbonari”. The ovens were made of various materials, including volcanic rocks. This one is made of metal. It was a cottage industry that families could earn a living with for a while because charcoal burns hotter than wood and was used to process ore that came out of the mines. The industry was eventually phased out by the discovery of coal, the shortage of timber and the cost of transportation of timber as the forests near the ovens were used up. After they were abandoned they were often used by stockmen, prospectors and even bank and stage robbers as shelter. Today they are still used by some campers who find shelter in them during an unpredictable storm in the Sierras.