 By the time Santa Clara County bought the mines in 1976 and ended operations, 1,137,727 flasks totaling of mercury (worth more than US$70 million) had been extracted.The remains of a variety of structures left over from the 135 years of mining activity, including housing for the up to 1,800 miners, are scattered about the park, with the biggest concentration at what was known as English Camp, established by Cornish miners in the 1860s.Some structures were built later by the U.S. Army Corps of Engineers and there is a memorial honoring the Civilian Conservation Corps firefighters who were stationed there for a time.