My great grandfather, Richard R. Williams,(B) St.Blazey, Corwall came just before 1870 & he+wife Susan were on 1870 census. They lived in Lake City(a mining town which no longer exists) & other family lived in Nevada City and North Bloomfield, as well as Dutch Flat, and Columbia Hill which was also known as North Columbia. The only mines I can think of off the top of my head are Empire & Lone Star mines. In 1884 the Sawyer Decision stopped the hydraulic mining in which whole hillsides were washed away by powerful jets of water to find the gold.I will ask my cousin who is 85 about other mines which she remembers.All my father's family were miners.They were poorly educated and drank a lot.Mostly poor moral standards also.Lots of scandals in our family!Also lots of children! No birth control then!