Copper Stain from Gilpin County, Colorado, USA
USA | |
| Lovering, T.S., Goddard, E.N. (1950) Geology and ore deposits of the Front Range, Colorado. Professional Paper 223. US Geological Survey doi:10.3133/pp223 |
| Emmons, S. F., Becker, G. F. (1885) Statistics and Technology of the Precious Metals. Bureau of the Census. |