These otherworldly "towers," located in California's Mono Lake, may look like eerie art installations, but they occur naturally and are made of limestone. Mono Lake is a shallow salt water lake located in the high desert on the eastern slope of the Sierra Nevada Mountains, in California in the United States. The lake has no outlet to the ocean causing high levels of salts to accumulate in the waters. These rock towers form when underwater springs rich in calcium mix with the waters of the lake, which are rich in carbonates. The resulting reaction forms limestone. Over time the buildup of limestone formed towers, and when the water level of the lake dropped the towers became exposed.