The Otho Mine was part and parcel of the infamous Black Hills "Tin Boom," running from 1883 until 1892. In 1883, an 'inexhaustible' deposit of cassiterite, a high grade ore of tin, was discovered about a mile up Greyhound Gulch at the Etta Mine. In 1884, a group of wealthy American and English capitalists formed the Harney Peak Consolidated Tin Mining, Milling and Manufacturing Company. This company proceeded to acquire some 1,100 tin claims in the Harney Range, perhaps the largest land grab in Black Hills history. Large milling operations were established at Hill City, Otho-Glendale and Etta Camp.

When large lodes of tin ore, presumed to lie beneath the surface, were not there to be found, British investors jumped ship in 1892, just as the large tin mills were being completed. The following litigation revealed corruption among the American investors which helped bring the Black Hills Tin Boom to an immediate halt. Local miners were not bothered much since gold-bearing quartz had been discovered in Keystone the year before and gold mining paid better money than tin mining.

The Otho Mine was established on the 9th of June in 1892. Three buildings remain, the bunk house, the cook house, and the office. The main entrance to the mine still exists as well as a cabin dating to the early 1900s.