Seen from South Tufa.

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.

This desert lake has an unusually productive ecosystem based on brine shrimp that thrive in its waters, and provides critical nesting habitat for two million annual migratory birds that feed on the shrimp. Mono Lake is also notable for containing GFAJ-1, a rod-shaped extremophilic species of bacteria that may be capable of metabolizing the usually poisonous element arsenic.

The human history of Mono Lake is associated with its productive ecosystem. The native Kutzadika'a people derived nutrition from the larvae of the alkaline flies that live in the lake. When the city of Los Angeles diverted water from flowing into the lake, it lowered the lake level, which imperiled the migratory birds. The Mono Lake Committee formed in response, winning a legal battle that forced Los Angeles to partially restore the lake level.

Mono Lake is a geologist's paradise. Currently, Mono Lake is in a geologically active area at the north end of the Mono–Inyo Craters volcanic chain and is close to Long Valley Caldera. Volcanic activity continues in the Mono Lake vicinity: the most recent eruption occurred 350 years ago, resulting in the formation of Paoha Island. Panum Crater (on the south shore of the lake) is an excellent example of a combined rhyolite dome and cinder cone.