The discovery of gold in California in 1848 brought large quantities of gold dust and gold nuggets of varying sizes to the market. This created an immediate need for assayers, refiners, and minters to turn the natural gold into forms of consistent size and purity for use by the local population and for shipment to external markets. This need was fulfilled by an assortment of individuals, associations, and quasi-governmental organizations. Profit was made in two ways: first, through fees charged for assays and second, through misrepresentation of the purity of the finished products. The latter method was used most often on coins, where the initial trust on the part of the public later turned to anger when assays revealed the debasement of the gold. The dishonest practices of some led to calls for an official solution, culminating in the establishment of an official U.S. Assay office in 1851 and a branch mint in San Francisco in 1854. Most of the privately issued California gold coins are extremely rare today because most were melted down and converted to "real" coins by the new U.S. mint.
This section includes a list of organizations that produced actual gold coins for circulation, as well as coins (not necessarily gold) that never made it past the pattern (or prototype) stage.