The Mount Ophir Mine was one of the most successful and conspicuous Mother Lode mines in Mariposa County. It included the Mount Ophir Mint, the first such mint to turn gold into coins. The mint was built by John Moffitt, who had been appointed to the Office of United States Assayer for California by President Tyler. It produced $50.00 octagonal coins, known as slugs, in 1850 and 1851 before the mint was established in San Francisco. The mine was worked extensively until 1914.