Round Lake Mine, part of the Johnsonville Mining District, was initially prospected during the Gold Rush but not fully developed until 1914. A stamp mill was built here in 1915 to extract the gold. Only a few feet of ground surface were gold bearing because the quartz vein extended under Round Lake and was covered by glacial debris. In 1918, miners built a shaft 300 feet deep, creating a tunnel that followed the gold-bearing solid quartz fissure 100 feet to the east and another 160 feet to the west under Round Lake. In 1935, the Ready Bullion Company of Sacramento built a second mill at a cost of $100,000, and a 400 foot incline shaft was built to reach under the lake. Shortly after they were built, the mill and shaft timbers burned to the ground, and the venture was abandoned. The remains of the mill survive here.