In 1849, one troy ounce of gold was worth $20. A $20 coin contained .9675 ounce of pure gold.
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Gold was discovered in 1848 in California by James W. Marshall at Sutter's Mill. This was the first of the Gold Rushes, though the Victorian goldrushes in Australia were the richest.
A large migration and immigration movement to the San Fransisco area in hopes of finding gold.