Mono Lake

Mono Lake is the remnant of the Pleistocene Lake Russell which, at its highest, covered some 700 square kilometers (270 square miles) of the Mono Basin. Terrace deposits and wave-cut cliffs formed by the older lake are visible at elevations up to 230 meters (750 feet) above the present surface level.

Mono Lake is a shallow-water body, its greatest depth being approximately 35 meters (120 feet), with no outlet. Within the lake are two large islands, Paoha and Negit. Both are of volcanic origin; the latter is almost entirely basaltic, while the former, and larger, was formed by volcanic uplifting of the lake-bed sediments. There is a hot spring on Paoha.

There are numerous springs, some hot, onshore and subsurface. Tufa deposits, consisting primarily of calcium carbonate, have been formed at and near the springs.

The lake water has a salinity approaching three times that of ocean water. While there are no fish, the lake supports very dense populations of the brine shrimp Artemia salina and of the Mono Lake fly, Ephydra hians, as well as several other invertebrates.

Some 62 species of water-oriented birds have been observed here. It is the site of the second largest breeding colony of California gulls, Larus californicus, in the nation, with over 40,000 individuals in 1978. This was halved in 1979 as a result of the lowering of the lake level. Up to 700,000 eared grebes, Podiceps caspicus, probably non-breeding migrants, have been counted on the lake. It is estimated that this represents approximately one-third of the world's population. Both the gulls and grebes feed primarily on the brine shrimp.

Migrating Wilson's and northern phalaropes, Steganopus tricolor and Lobipes lobatus, occur here in great numbers, with counts as high as 93,000 and 21,600, respectively. The phalaropes feed primarily on the Mono Lake fly. There is also a breeding population of the snowy plover, Charadrius alexandrinus.

Excepting the marshy areas on the shore, vegetation of the recently exposed lake bottom is sparse, with some salt grass, Distichlis spicata. Above the more recently exposed floor, scrub is the dominant vegetation and includes such species as greasewood, Sarcobatus vermiculatus, sagebrush, Artemisia tridentata, bitterbrush, Purshia tridentata, rabbit brush, Chrysothamnus nauseosus and Chrysothamnus viscidiflorus. The marsh areas contain a variety of species including Scirpus spp., Typha spp., Puccinellia nuttalliana, Cleomella parviflora and the non-native Bassia hyssopifolia.

Integrity: Since 1940 the diversion of freshwater streams flowing into the lake has resulted in a drop of 13 meters (43 feet) in the surface level. This lowering of the water level has formed a land bridge to Negit Island, allowing predators to deplete the colony of gulls. Current plans call for the raising of the water level to protect the island.

Use: Research, educational, observational.

Ref: Winkler, D. W. (ed.), 1977. An Ecological Study of Mono Lake, California. Davis: Inst. of Ecology.

March 1980