Big Thunder Gold Mine (originally named Gold Hill Lode) was discovered in 1892 by two German immigrant miners. Today, it contains the most types of rocks, structures and minerals indigenous to the area, and it offers mine tours, a mining museum and gold panning. There is also a full-service eatery and a gift shop. Located in Keystone, we are open daily, April through October (see our hours online). We are open by reservation only, November through March.