Tufa limestone columns on Mono Lake, California.

Mono Lake is a large, shallow saline lake in Mono County, California.
The lake has been formed at least 760,000 years ago as a terminal lake in a basin that has no outlet to the ocean. Because it lacks an outlet, dissolved salts make the lake very alkaline and saline.

Perhaps the most intriguing of Mono Lake's phenomena are the tufa (pronounced "toofah") towers visible along much of the shoreline. Tufa are made from calcium carbonate which makes its way into the lake from underground springs. The calcium and carbonate combine to form limestone which builds up over time around the lake bottom spring openings. Declining lake levels have exposed the tufa towers we see today. Some of these tufa towers are up to 30 feet high.