Mono Lake is a 70 square-mile saline lake at the eastern foot of the Sierra Nevada Range, approximately 13 miles east of Yosemite National Park. Enclosed within a natural basin by the Sierra Batholith to its west and Pliocene-Pleistocene volcanic ranges to its north, east and south, the lake is fed by three primary streams (Lee Vining, Rush and Mill Creeks) and by freshwater springs along its floor. Having formed during the Pleistocene, about 1 million years ago, it is one of the oldest lakes in North America and is the largest lake completely within California.
As a basin lake, its size and depth are a balance between inflow from streams and springs and evaporative loss in the dry climate of the Basin and Range Province. Prior to 1941, its surface elevation hovered above 6400 feet but this was dramatically lowered by diversion of inflow to the Los Angeles Water System; legal challenges by conservation groups eventually restored most of the inflow by 1994.
Despite its high salinity (2.5 times that of ocean water) and alkalinity (which precludes fish survival), Mono Lake supports a spectacular ecosystem. Photosynthetic algae, feeding on minerals from the surrounding mountains, bloom in spring when snowmelt peaks. Feeding on the algae, brine shrimp and brine flies thrive in the lake shallows and provide vital nourishment for migrating shorebirds, eared grebes and phalaropes, among other species; indeed, Mono Lake was added to the Western Hemisphere Shorebird Reserve Network in 1991. California gulls and snowy plovers nest on Paoha Island and smaller islets, escaping predation by fox and coyotes. Beyond the abundant birdlife, Mono Lake is perhaps best known for its tufa towers of calcium carbonate, produced by the interaction of freshwater springs and the alkaline, mineral-rich lake waters. Students of geology will also appreciate the surrounding volcanic landscape, including the relatively recent Panum and Mono-Inyo craters, south of Mono Lake.
