California Caverns

California Cavern is a limestone cave in the Sierra Nevada foothills, in Cave City, Calaveras County, California. The series of interconnected caverns are one of the earliest officially recorded caves in the Mother Lode region of California. Although one of numerous caves in the Mother Lode region, California Caverns claims the distinction of having the most extensive system of caverns and passageways.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).