Mono Lake is an alkaline and hypersaline lake in Mono County, California on the eastern side of the Sierra Nevada.
It has an unusually productive ecosystem, and is a critical nesting habitat for several bird species.
It is believed to have formed at least 760,000 years ago, dating back to the Long Valley eruption. Sediments located below the ash layer hint that Mono Lake could be a remnant of a larger and older lake that once covered a large part of Nevada and Utah, making it among the oldest lakes in North America.
At its height during the last ice age, the lake may have been 900 feet (270 m) deep.
It is the terminal lake in a watershed fed by melting runoff, with no outlet to the ocean. Dissolved salts in the runoff
thus remain in the lake and raise the water's pH levels and salt concentration.