Mono Lake is a State Natural Reserve that was established to preserve the spectacular "tufa towers," calcium-carbonate spires and knobs formed by interaction of freshwater springs and alkaline lake water. Mono Lake is a majestic body of water covering about 65 square miles. It is an ancient lake, over 1 million years old -- one of the oldest lakes in North America. It has no outlet. Throughout its long existence, salts and minerals have washed into the lake from Eastern Sierra streams. Freshwater evaporating from the lake each year has left the salts and minerals behind so that the lake is now about 2 1/2 times as salty as the ocean and very alkaline.

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. The lake is famous for the Mono Lake brine shrimp, a tiny species of brine shrimp, no bigger than a thumbnail, that are endemic. During the warmer summer months, an estimated 4-6 trillion brine shrimp inhabit the lake. Brine shrimp have no food value for humans, but are a staple for birds of the region. The brine shrimp feed on microscopic planktonic algae which reproduce rapidly during winter and early spring after winter runoff brings nutrients to the surface layer of water. The whole food chain of the lake is based on the high population of single-celled algae present in the warm shallow waters. By March the lake is "as green as pea soup" with photosynthesizing algae. Alkali flies, live along the shores of the lake and walk underwater encased in small air bubbles for grazing and to lay eggs. These flies are an important source of food for migratory and nesting birds.

Mono Lake is a vital resting and eating stop for migratory shorebirds and has been recognized as a site of international importance by the Western Hemisphere Shorebird Reserve Network. Nearly 2,000,000 waterbirds, including 35 species of shorebirds, use Mono Lake to rest and eat for at least part of the year.

The unusual rock formations that grace Mono Lake's shores are known to geologists as tufa (too'-fah). Tufa is essentially common limestone. What is uncommon about this limestone is the way it forms. Typically, underwater springs rich in calcium mix with lakewater rich in carbonates. As the calcium comes in contact with carbonates in the lake, a chemical reaction occurs resulting in calcium carbonate--limestone. The calcium carbonate precipitates (settles out of solution as a solid) around the spring, and over the course of decades to centuries, a tufa tower will grow. Tufa towers grow exclusively underwater, and some grow to heights of over 30 feet. The reason visitors see so much tufa around Mono Lake today is because the lake level fell dramatically after water diversions began in 1941.