Nestled at the edge of the arid Great Basin and the snowy Sierra Nevada mountains in California, Mono Lake is a saline soda lake formed at least 760,000 years ago as a terminal lake in an endorheic basin. The lack of an outlet causes high levels of salts to accumulate in the lake. These salts also make the lake water alkaline. This desert lake has an unusually productive ecosystem based on brine shrimp that thrive in its waters, and provides critical habitat for two million annual migratory birds that feed on the shrimp and alkali flies. Along the lakeshore, scenic limestone formations known as tufa towers rise from the water’s surface.