Because the forces of erosion and gravity tend to carry lighter materials like quartz away more easily, the heavy minerals like gold or silver will tend to be concentrated in the general area around the vein outcrop. These concentrations are what make residual placers so attractive.

The Oatman/San Francisco Mining District’s historic gold production of 2.2 million ounces of gold since the 1880s makes this area Arizona’s greatest primary gold producing district.