References Consulted

 Background Information
Mono Lake
California

General statements and explanation of the Geographic Summary are a result of field observations by the WETMAAP Team and a composite of information from multiple sources including reports, articles, books, Internet accessible data, and interviews with experts on Mono Lake’s changing lake levels and wetland change.General information from multiple sources and data from Internet websites are not specifically cited.Much of the information compiled in this summary is from the Mono Lake Committee Website. WETMAAP thanks the Mono Lake Committee for their contribution to this project by giving permission for the unrestricted use of information from their website References Consulted, located at the end of this geographic summary, lists the specific Mono Lake Committee webpages used for this summary as well as other sources.

Note:  The Geographic Summary is a compilation of information from existing sources and is intended to provide a brief synopsis of the Mono Lake area, changes in lake level, and wetland changes.It is not meant to be an in-depth treatise on the geography and background of the area.

The Physical Setting and Settlement History

Mono Lake, one of the oldest lakes in North America, is located on the western fringe of the Basin and Range province, and east of Sierra Nevada Mountains.  This unique lake is approximately 140 miles south of Reno, Nevada and 340 miles north of the City of Los Angeles (Figure 2.1).  During the Pleistocene Age glacial melt water produced the highest level of Mono Lake causing it to overflow into the Owens River Gorge and drain south into a large glacial lake in the Owens Valley.  Below this highest level Mono Lake has no outlet. The only natural way for water to leave a terminal lake is through evaporation, which causes minerals and trace elements present in the run-off to become concentrated in the water that remains in the lake.  This process, combined with thousands of years of time, has resulted in a lake that has a pH of 10 and salinity 2-3 times greater than that found in the ocean.  The runoff from the Sierra Nevada Mountains has been the primary source of these minerals and trace elements in the past.  Currently, physical alterations including road construction and retreating lake levels have changed the landscape and hydrology affecting the flow of groundwater.  An area of current concern for the leaching of minerals by groundwater is the Mono Craters south of Mono Lake.  Runoff is causing the leaching of naturally occurring minerals found in these volcanic craters that may be hazardous to humans and wildlife.

Settlement History

Although it would appear that the water chemistry of Mono Lake would make the lake unsuitable for life, nothing could be further from the truth.>Mono Lake and Basin have supported life for thousands of years.There is evidence that humans may have walked

Figure 2.1: Location of Mono Lake

the shores of Mono Lake as early as 5,500 years BP.During the summer months, the early inhabitants would harvest alkali fly pupae, or Kutsavi, which was an excellent source of protein and was easy to obtain.These early people became known as Kutzadika’a, or the “fly eaters”.The alkali fly pupae food source combined with abundant waterfowl of Mono Lake, allowed the Mono Basin to seasonally support a community of 200 people.

Even though the Kutzadika’a lived in the Mono Lake area for thousands of years, the area was accidentally discovered by European Americans in 1852 by a group of cavalry soldiers who were in pursuit of a band of renegade Miwock Indians from the Yosemite area.While the Indians were never captured, many intriguing ore samples were found in the area of Mono Lake.The news of these ore finds spread and miners descended on the Mono Basin hoping to make their fortunes.The immediate area around Mono Lake was not the source of any large strikes.Substantial veins of silver, however, were found in the area north of Mono Lake near the towns of Bodie and Aurora.These two towns became part of the “boom and bust” cycle prevalent in many areas of the American West. These communities swelled in size with the news of a silver strike, only to shrink and, in some instances, die when the silver played out. Some settlers moved to the Mono Basin during the gold-strike era hoping to make their living from the land.Some were able to survive by supplying the mining towns with locally grown food. Today, the remains of some of early homesteads can still be found in the Mono basin.While some of the early settlers made their living with cash crops, others made their fortunes by supplying Bodie, Aurora, and other mining towns with timber harvested from the southern portion of the Mono Basin.One of the most successful individuals in this industry was Lee Vining; the town that bears his name is still an important community in the Mono Basin.

The Mono Lake and Basin area remained a profitable place for agriculture until the Great Depression of the 1930’s. As a result of the Depression, many landowners were unable to survive financially and were forced to leave the region. As well, during the 1930’s, the Los Angeles’ Department of Water and Power (LADWP) realized that they would eventually need to extend their aqueduct north to meet the increasing demand for water in Los Angeles.  The LADWP bought large tracts of land from individuals in the Mono Basin, and in larger measure, bought most of the water rights in the Mono Basin.These acquisitions have made Los Angeles the second largest landholder in the Mono Basin, with only the federal government owning more land in this area.

Geology

Geologists’ estimate the age of Mono Lake ranges between 1 million and 3 million years. While the exact age of Mono Lake is a source of a controversy, it is generally agreed that the lake has held water for over 700,000 years BP.  The debate over the age of the lake arises largely from a test oil well that was drilled on Poaha Island in the early 1900’s.  The workers, after drilling through several hundred feet of sedimentary rock, discovered a layer of ash, then more layers of sedimentary rock.  The layer of volcanic ash dates to the Long Valley Eruption approximately 760,000 years BP. This means that the sediment layers beneath the ash are older than 700,000 plus years.

Approximately 3 million years BP (Before Present), the Mono Basin became a closed depressional feature through a combination of block faulting along the eastern scarp of the Sierra Nevada and from a down warping of the north and south sides of the Basin. The Basin closure has continued to be accentuated by the volcanic activity along the southern margins of the Basin.

The Mono Basin is of great interest to geologists because this area has continued geologic activity.The Mono Craters south of Mono Lake are plug dome volcanoes.Cooled lava forms a huge dome shaped structure that “plugs” the vent in the bottom of the crater.The Mono Craters are relatively young, with eruptions forming the first of these volcanic domes about 100,000 years ago. A few eruptions occurred 100,000 years ago, however, the majority of the Mono Craters formed in the last 10,000 years.Panum Crater, the newest crater of the group, was formed in an eruption approximately 650 years ago.Because Panum Crater is a geologically young volcano, erosion factors have had minimal impact on its features.While Panum Crater is the most recent extrusive volcanic feature to form in the Mono Basin, the most recent example of volcanic activity is Poaha Island, which is the larger of the two islands in Mono Lake.Poaha Island formed about three hundred years ago when lake bottom sediments were pushed upward by magma that lacked the force to break through to the surface.Steam vents and fumeroles present on the island suggest that the volcanic activity within Poaha Island may not be dormant.

The geologic history of the Mono Basin is intense and impressive, and the most dynamic aspect of the Basin is that it still tectonically active with evidence of faulting and volcanic activity within the Basin and the Mono Craters.An 11.5 mile tunnel was drilled through the Mono Craters during the 1930’s while extending the aqueduct system for LADWP. Work crews drilling the tunnel observed steam, hot groundwater, and carbon dioxide, all of which indicate volcanic activity.From the geologic record evidence of a volcanic eruption occurs about every 500 years in the Mono Basin, a cycle that has been occurring for a several thousand years, and perhaps a possible calendar of future events.

Topography

Mono Lake lies in a tectonic basin surrounded on all sides by mountains.The Sierra Nevada Mountains are to the west of the lake. Mt. Warren, located in the Sierra Nevada’s within sight of Mono Lake, is over a mile higher in elevation than the surface of the lake.The Bodie Hills to the north and the Cowtrack Mountains on the east side of the Mono Lake are the remains of earlier volcanic activity that occurred before Mono Lake existed. The Mono Craters are south of the lake with the highest of the plug domes over 9000 feet in elevation.

The Mono Craters, Bodie Hills, and Cowtrack Mountains constitute the majority of topographic features in the Mono Basin; however, there are three other topographic points that are also of volcanic origin.  Black Point, currently on dry land, located on the northwestern shore of Mono Lake and easily recognized because it is a short, flat-topped, black hill with deep fissures on its southwest side, is believed to have erupted under hundreds of feet of water when Mono Lake was considerably larger.  Negit, the smaller of the two islands located in Mono Lake, is also of volcanic origin.  Paoha is the larger of the two islands located in Mono Lake and more closely resembles a dried mud flat. 

Mono Lake’s terraced shorelines are a result of lake retreat, and contribute to the excessive exposure of one of the Basin’s most striking features, tufa towers.  These pale gray limestone towers form underwater and are exposed as the level of the lake decreases.  The tufa towers are very common in many alkaline lakes worldwide.  Tufa is formed from a simple chemical reaction of a few very abundant elements in the lake environment.  Calcium rich water bubbles up from springs in the lake combining with the carbonate saturated water of the lake to form calcium carbonate.  This calcium carbonate forms a tower around the spring and continually grows as long as the spring is submerged in the water.  Tufa is estimated to grow as much as an inch per year.

Precipitation

Mono Lake lies in the rainshadow on the eastern side of the Sierra Nevada Mountains.The annual precipitation in Mono Lake averages 6 inches.Thunderstorms, some of which may be intense and localized, are the primary source of summer rainfall with the Mono Basin.

The high elevations of the Sierra Nevada receive an average of 50 inches of precipitation.Most of the high elevation precipitation falls as snow, which may occur year-round with the highest accumulations between October and March.

Water

Surface Runoff

Five major streams, plus a number of small streams, originating in the Sierra Nevada, Bodie Hills, Cowtrack Mountains, and Mono Craters uplift drain into Mono Lake.Snowmelt begins in April and continues through June with maximum runoff in May and June. Because the runoff from snowmelt is highly seasonal, approximately 40 % of the total annual flow occurs in the late spring and early summer.

Groundwater

Since the Mono Basin is a structural and depositional basin, the movement of groundwater flows from the edges toward the center of the basin that is occupied by Mono Lake.The Basin is filled with layers of lake lacustrine, alluvial, colluvial, and glacial sediments that are unconsolidated to poorly consolidated allowing unimpeded flow of groundwater through the layers.Recharge areas are found within the higher mountains and hills surrounding the basin.The flow of groundwater will vary between 175 feet of the basin sediments to shallow depths of less than 3 feet or on the surface near the lakeshore.Mono Lake is a groundwater sink for the Basin.Groundwater is discharged at springs and seeps underneath the lake or near the lakeshore.

Lake Evaporation

The LADWP in 1987 estimated the annual evaporation rate to be 42 inches per year. This makes evaporation approximately 50 % of the total lake water loss.

Prehistoric and Historic Fluctuations

During the last stage of Pleistocene glaciation, approximately 23,000 to 12,500 years ago, the level of the lake in the Mono Basin was 7 times deeper and 5 times larger than it is today.The Pleistocene lake in the Mono Basin has been named Lake Russell.At the time that it reached its maximum extent, approximately 23,000 years BP, it carved a glacial spillway into the Owens River Gorge draining into the Owens Valley.The Lake has reached several low stands during pre-historic and historic times including a glacial stand at approximately 6,600 feet above sea level and at approximately 1,850 year BP the Lake was at its lowest stand ever.The former would have been a couple of hundred feet higher than the present day lake level and the latter would have been approximately 20 feet below the current lake level.

Water Before 1941

When Mono Lake first formed, it was just one of the many lakes that were prevalent in the Great Basin of North America.The majority of these lakes have disappeared mainly due to climatic changes that have occurred in the last 15,000 years. Mono Lake water levels have fluctuated widely during the climatic changes of the last 15,000 years. When Mono Lake was fed by glacial meltwaters after the last ice age, approximately 12,500 years BP, the surface area of the lake was almost 340 square miles with a depth nearing a thousand feet in the deepest areas of the lake.This ancient lake had a surface area of almost five times the current level and was nearly 800 feet deeper than Mono Lake currently is today. Before 1941, the level of Mono Lake appeared to have stabilized at 6,417 feet above sea level with the highest recorded level this century in 1928 with a height of 6,428 feet above sea level.These levels no longer exist and will probably never occur again because of the actions of the LADWP in 1941 and because of other human alternations to stream drainage and to watersheds.

Water 1941 to 1994

In 1941, the LADWP began diverting water from Mono Lake.The water in Mono Lake is not potable, however, the five streams that drain into the lake consist of fresh water derived from the snow melt in the Sierra Nevada range.The LADWP recognized this seemingly abundant source of pure water and diverted four of Mono Lake’s tributaries to serve as a source of water for Los Angeles.The extreme reduction in lake inflows caused the Lake to decline by 45 feet to 6,372 feet above sea level in 1982; which was the lowest recorded level for the Lake. During this period of tremendous water export, 18,000 acres of former lake bottom were exposed due to the receding water level.

In 1994, after more than a decade of legal battles, the California State Water Resources Control Board issued an order (D.1631) protecting the lake and the tributaries draining into it.The order called for minimum flows to be maintained in all diverted streams. The order implemented a plan that will raise the level of Mono Lake to 6,392 feet above sea level or 17 feet higher than it was when the order was issued.It is expected to take approximately 20 years for the lake to stabilize at this level.

Water 1994-Present

Since the fall of 1994 when D1631 was implemented, the level of the Mono Lake has risen approximately 10 feet.The lake level in October of 1999 was 6,384.4 feet above sea level, while the level of the lake as of May 27, 2000 was 6,384.5 feet above sea level with only 9,300 acres of the pre-1941 lakebed still exposed(Table 2.1). When the lake reaches its stabilized level by 2014, it is projected that there will be only 6,000 remaining acres of the pre-1941 lakebed exposed. The area of the lake will have grown by an estimated five square miles and the salinity will be approximately 10% less than today’s levels. While it appears that Mono Lake will reach 6,392-foot level, a few years of diminished snowfall amounts in the Sierra Nevada’s could impact the future rates of lake level increases.

Realizing that the demand for water will always be a concern, the Mono Lake Committee and LADWP are working together to develop new strategies and methods to conserve and recycle this precious resource. The East Valley Reclamation Project was implemented through the combined efforts of the Mono Lake Committee and Los Angeles Department of Water and Power. The reclamation project will eventually supply over 30,000 acre-feet of recycled water per year.This will constitute approximately 40% of the 78,000 acre feet of water that was lost when the order to restore Mono Lake was implemented.The Mono Lake Committee and Los Angeles Department of Water and Power also have worked together to implement a low flush toilet program that distributes low flush toilets free of charge to homeowners, thus stretching water supplies even farther.

Table 2.1:Mono Lake Level 1850-1998

Through these programs and many others, the water used by Los Angeles has declined to levels of use in the mid -seventies. Water reduction has occurred even though the population has increased by over a million people in this same period of time.

Vegetation

Wetland Habitats As the lake level of Mono Lake receded, patches of emergents and shrubs dominated the vegetation that became established on the exposed flats. The patchiness is a result of a series of localized environmental conditions of, primarily, soil salinity and available moisture. Precipitation, depth to the water table, the amount of spring and seep flow, and the extent of salt deposition in the soil from evaporation are factors that influence the environmental conditions around the lakeshore.

While lake levels have decreased and some shallow water habitats have been lost, the change in the phreatophyte communities (plants with roots that extend to the groundwater table, and usually grow around the edges of lakes and playas) has increased from 170 to 1,360 acres between 1940 and 1978. These phreatophytes include emergent marsh of Scirpus spp. and Juncus spp., and scrub-shrubs of willow Salix spp. and Sarcobatus vermiculatus.

A typical transect from the shoreline will include the following communities and species:

The first 1-6 foot of elevation increase will be barren or very sparse salt tolerant vegetation species.  Next, the saltgrass, Juncus spp. in particular, will increase in density from sparse to dense. 

Marsh grass habitat will develop from the water source to the lake edge if there is a spring or seep available with freshwater on or moistening the surface.  This area will be dominated by Scirpus spp.  Some wet areas around springs, or along the seep line, will support scrub-shrub species of willow. 

The edge of the emergent marsh will transition into dry upland scrub-shrub and upland range habitats of Sagebrush (Artemisia tridentata) and Rabbitbrush (Chysothamnus spp.).  This will occur between 5 and 12 feet vertical elevation above the lake level.  Typically, in this scrub-shrub sagebrush habitat, the plants tolerant of high salinity and a water table closer to the surface may be found closer to the shoreline, and consist of Chrysothamnus nauseousus mixed with emergent marshgrass.  Conversely, Artemisia tridentata will dominate the upland scrub-shrub and upland range habitats where the water table is greater than one meter below the surface.

Riparian vegetation dominates the streams that drain into Mono Lake.  The riparian vegetation will vary from very sparse in the dryer stream bottoms and on the alluvial fans to a dense streamside growth of woody trees.  The riparian vegetation at the mouths of the streams as they discharge into the Lake has undergone several changes as lake levels have increased and decreased.  The streams have incised into the glacial outwash and lake sediments, cutting narrower valleys and producing small deltas at the shoreline.  As the discharge levels of the streams have decreased over time these deltas have become subaerial providing additional habitats of scrub-shrub rather than shallow water inundated emergents.

Farther up the slopes of the Sierra Nevada front the pinyon-juniper scrub-shrub woodland is evident.  However, because of low precipitation availability due to the rainshadow effect on the eastern side of the Sierras, this woodland is comprised of stunted tree growth and is dominated by Artemisia tridentata and Purshia tridentata.

Vegetation and Wetland Changes

Historically, Mono Lake contained numerous types of wetland habitats to support the large numbers of migratory waterfowl that used the lake.Today the wetland habitats of the pre-diversion days have declined or changed because declining water levels have caused the degradation and loss of large areas of wetlands.It is estimated that before the diversions began, lagoons, fresh water marshes, and creek deltas accounted for approximately 900 acres of wetland habitat.This estimate does not include the speculative one mile long lagoon at Simmons Point.

The diversions that began in 1941 did not have an immediate impact on the vegetation and habitats of Mono Lake.The first noticeable effect of the diversions occurred when the lake level fell below 6,405 feet above sea level.When the lake fell below this level, the large lagoons that were on the northeastern shore of the lake disappeared. The level below 6,405 was reached in 1957 or 16 years after the diversions began. Throughout the 1960’s as the lake level declined, more habitats were lost, primarily at creek deltas as freshwater creeks incised their stream beds. Incision, reduced stream flows, and questionable water discharge practices contributed to the additional loss of approximately 200 acres of riparian plant growth along Mono Lake’s four main tributaries.

Although there has been a reduction of shallow lagoon areas, the areas of marsh, wetland scrub, alkali meadow and wet meadow have increased substantially.With this increase, however, the habitat types around the lake have changed, thus affecting the quality and functions of the vegetation and open water.In particular, the change in wetland types has produced more less-desirable habitats for most waterfowl.

When areas of lakebed are exposed, a layer of efflorescent salt forms on the surface of the former lakebed.This salt is one of the main ingredients of the alkali dust along with the soil from poorly vegetated areas of the former lakebed. On windy days alkali dust from the exposed former lakebed becomes wind-born affecting air quality, visibility, and corrosion.

In addition to raising the level of the lake, D.1631 provides for the restoration of streams and the riparian corridors of growth that follow these streams.The restoration projects will be accomplished through the use of various techniques including the re-watering and elimination of grazing on riparian vegetation.Hand labor, heavy equipment and fire have been and are still currently being used to clear channels and creek deltas to improve their productivity. As the lake and stream levels have increased, the emphasis has been placed on allowing streams to mimic natural flows so that riparian vegetation can reestablish itself in a more natural manner.

Specific Environmental Concerns

Bird Nesting Ground

The waters of Mono Lake are too alkaline to support any species of fish, however, brine shrimp are abundant. The high alkalinity of the lake supports a very unique and robust ecosystem that attracts millions of migrating birds each year. Significant numbers of Eared Grebes, Wilson’s Phalaropes and Red-necked Phalaropes use the lake as a primary stopover point along the migration routes to and from Central and South America each year. The birds forage on the brine shrimp and alkali flies that thrive in the saline waters of the lake. Mono Lake also is the nesting ground for large numbers of California Gulls; the only place in the world having a higher concentration is the Great Salt Lake in Utah. The gulls at Mono Lake used Negit Island as one of their primary nesting sites until 1977 when the excessive diversions of water caused the level of the lake to drop low enough for a land bridge to develop. This allowed predators to feed on the birds and their nests. Consequently, the gulls moved their nesting site to some of the small islands around Negit Island, but it is undetermined how much of an effect this relocation had on the gull population of the lake. Mono Lake also hosts the nesting grounds for more than 10% of California’s breeding population of Snowy Plovers and numerous other species of ducks, geese and other water birds.

In the past, over one million ducks migrated to Mono Lake annually. Even though these numbers of waterfowl are impressive, some species of waterfowl that used the lake have declined to 1% of their pre-diversion numbers. A major reason for this decline is the decreasing inflow of freshwater. Mono Lake, although highly alkaline, has freshwater environments at the mouths of the streams flowing into the lake -- a phenomenon known as hypopycnal stratification. Hypopycnal stratification is the condition in which low density freshwater floats on the top of the denser water of the lake before mixing. This layer is an ideal habitat for ducks because they are able to feed on the brine shrimp and alkali flies above, below, and at the edges of this environment. Consequently, as inflows have decreased, these habitats have decreased in size and carrying capacity, thus reducing the number of ducks using the lake.

Fragile Ecosystem

Fragile, hardly seems the appropriate word to use in a description of any part of an ancient lake. A lake that has seen glaciers come and go and volcanoes erupt on its shores, but fragile is a very accurate description of the ecosystem of Mono Lake. Brine shrimp and alkali flies have adapted to the environment of Mono Lake after many thousands of years; however, as the salinity of the lake has increased due to diversions the numbers of brine shrimp and alkali flies present at Mono Lake has decreased. This can be attributed to the fact that more energy is needed to survive in the increased salinity so less energy is available for growth and reproduction. If the alkalinity had increased naturally over time the flies and shrimp would have been able to adapt to the changes over many generations. As it was the alkalinity of the lake almost doubled in a fifty year period.

It is anticipated that as the lake level increases the number of brine shrimp, alkali flies and acres of hypopycnal habitat will increase. The National Forest Service has also recognized the need for the protection of nesting areas around the lake and has imposed numerous restrictions on how close individuals can get to these nesting areas. It is hoped that these measures will make the lake more desirable to larger numbers of waterfowl in the future.

The importance of this lake cannot be disregarded. While Mono Lake can never be returned to it’s pre-diversion state it is hoped that through the efforts of the Mono Lake Committee, National Forest Service, and numerous other organizations that Mono Lake will continue to be an important part of the ecosystem of the western hemisphere for many years to come.

Facts and Statistics