This collection consists of pages of unbound printed forms on which daily assay samples
are recorded, giving the percentages of copper, iron, etc. in each sample. Since the
period covered by these records includes the World War I years, the data displayed may
show an increase in mining activity in response to war needs.
Campo Seco, eight miles southwest of Mokelumne Hill in Calaveras County prospered briefly
as a gold mining camp (1850-1860), but in later years was known principally for its
production of copper and zinc, most notably from the Penn Mine. In 1887 the Penn Chemical
Co. acquired a mining site and erected a smelter (1899) which served the Penn mines
through 1919. The smelter was equipped with a crushing and grinding plant, eight roasting
furnaces and a blast furnace. The smelter was shut down and dismantled when the price of
copper declined following World War I. Gross returns from the smelting operation exceeded
Collection is open for research.