Lake Cahuilla ( ; also known as Lake LeConte and Blake Sea) was a prehistoric lake in California and northern Mexico. Located in the Coachella and Imperial valleys, it covered surface areas of to a height of above sea level during the Holocene. During earlier stages of the Pleistocene, the lake reached even higher elevations, up to above sea level. During the Holocene most of the water came from the Colorado River with little contribution from local runoff; in the Pleistocene local runoff was higher and it is possible that Lake Cahuilla was supported solely from local water sources during the Wisconsin glaciation. The lake overflowed close to Cerro Prieto into the Rio Hardy, eventually draining into the Gulf of California.
The lake formed several times during the Holocene, when water from the Colorado River was diverted into the Salton Trough. This tectonic depression forms the northern basin of the Gulf of California, but it was separated from the sea proper by the growth of the Colorado River Delta. Such changes in river courses may have been caused by earthquakes among the numerous faults that cross the region, such as the San Andreas Fault. Conversely, it is possible that the weight of the water itself triggered earthquakes. During its existence, Lake Cahuilla formed strandlines and various beach deposits such as gravel bars and travertine deposits.
The lake existed in several stages over the last 2,000 years, periodically drying and refilling and eventually disappearing sometime after 1580. Between 1905 and 1907, due to an engineering accident, the Salton Sea formed in parts of the lower basin of Lake Cahuilla. Were it not for human intervention, the sea might have grown to the size of prehistoric Lake Cahuilla. Today the former lake bed forms the fertile regions of the Imperial and Coachella Valleys.
The Algodones Dunes were formed from sand deposited by Lake Cahuilla, which was transported by wind toward the area. During its existence, the lake supported a rich biota with fish, bivalves and vegetation on its shorelines. These resources supported human populations on its shores, as evidenced by a number of archeological sites and mythological references to the lake in the traditions of the Cahuilla. The lake may have had profound effects on population genetics and language history of the surrounding regions.
Name
The name "Lake Cahuilla" was used in 1907 by William Phipps Blake and is sometimes spelled "Coahuila". The lake is named after the Cahuilla, who refer to the lake in their oral tradition. A second name is "Blake Sea", after William Phipps Blake, who during one of the Pacific Railroad Surveys recognized the deposits of the former lake. According to their mythology, the Salton Trough was created by their deities Mukat and Témayawet to pool water.
The name "Lake LeConte" was coined in 1902 by Gilbert E. Bailey, and it is occasionally used to refer to the lake that existed during the Wisconsin glaciation or Pleistocene. In 1980, M.R. Waters applied the term to cover all lakes of Holocene age in the Salton Basin. This name is derived from Joseph LeConte, a geography professor.
Presently, the name "Lake Cahuilla" applies to the reservoir at the northern end of the Coachella Canal, in the Coachella Valley. "Lake Cahuilla" is also the name of a seismic station in California.
Geography
Lake Cahuilla formed in the region of the present-day Salton Sea. It extended over the southern end of Coachella Valley in the north, through the Imperial Valley in the south, and down to the Cerro Prieto area in Baja California. The general area is also known as the Colorado Desert. Currently, of the land is below sea level. The Salton Trough extends northwest and has a width of at the border.
Towns in areas formerly covered by Lake Cahuilla include, from north to south, Indio, Thermal, Mecca, Mortmar, Niland, Calipatria, Brawley, Imperial and El Centro. Calexico and Mexicali may have been covered as well. To the southeast, the New River and the Alamo River now flow through the dry lakebed, while the Whitewater River and the San Felipe Creek enter from the northwest and southwest, respectively.
Major shorelines existed at above North American Datum (NAD) and at above NAD. With a southern shore south of the US-Mexico border, Lake Cahuilla had a length of , a maximum width of and reached a depth of approximately at a water elevation of . The maximum surface area was about . The lake at maximum level held about - of water. At maximum size, Lake Cahuilla was considerably larger than the Salton Sea and almost as large as the entire Salton Trough, and constituted one of the largest lakes of Holocene North America.
Bat Caves Butte and Obsidian Butte formed islands in the lake when it was full although during highstands the latter was submerged. Relatively straight northwest–southeast trending eastern shores faced from northwest to southeast the Indio Hills, the Mecca Hills, the Orocopia Mountains, the Chocolate Mountains and the East Mesa. The less regular western shore faced the Santa Rosa Mountains towards north and the Fish Creek Mountains and Vallecito Mountains farther south. Earlier lake stages may have extended into the Jacumba Mountains as well.
Hydrology
Inflow
Lake Cahuilla was formed by water from the Colorado River; groundwater and other inflows were negligible. Likewise, the precipitation (presently about ) did not contribute much to the lake budget. The amount of water needed to sustain Lake Cahuilla at a level of above sea level is possibly about half of the discharge of the Colorado River, and during times where the lake was filling nearly no water from the river would have reached the Gulf of California.
Sedimentation of the Colorado River Delta directed water into the Lake Cahuilla area, a process that was more likely to happen during humid periods. Distributaries in a river delta are inherently unstable and tend to change course often. Major floods may have triggered the change in river course, although most of the flood events in the prehistoric record do not appear to be associated with diversions to Lake Cahuilla and one cannot conclude that the river course changes are more likely to occur during wet periods. Given that the slope toward Lake Cahuilla is steeper than the one toward the Gulf of California, once the river entered the basin it likely stabilized on that course. In fact, it is remarkable that this slope difference doesn't regularly cause the river to enter the Salton Trough. The diversions occurred close to the apex of the Colorado River Delta and would have discharged water directly through the Alamo River and indirectly through Volcano Lake and the New River into Lake Cahuilla. The infilling of the lake may have been a catastrophic flood, considering that native people fled the Imperial Valley to the mountains. Infilling to an altitude of above sea level would have taken 12–20 years. When the lake was full, the Colorado River would have entered it at the southeastern side.
When the Colorado River drained into Lake Cahuilla, the entire sediment flow ( ) of the river would have entered the lake; a sedimentation rate of has been inferred for the northern part of the lake while the Colorado River Delta shows evidence of reduced sedimentation while the river drained into Lake Cahuilla. Sedimentation of the inlet during highstands and resulting river course changes away from Lake Cahuilla would have resulted in the Colorado River changing its course back to the Gulf of California.
Other major streams that drained into Lake Cahuilla were Whitewater River from the north, and San Felipe Creek and Carrizo Creek from the southwest. More minor drainage came from Arroyo Salado on the western shore, and Salt Creek and Mammoth Wash on the eastern shore. Additional unnamed drainages did exist. Drainage from the Chocolate Mountains and the Cargo Muchacho Mountains may have reached the lake but are now buried by the Algodones Dunes. All these water systems are ephemeral.
Presently the only major streams entering the basin come from mountains to the west and northwest, as well as the New and Alamo Rivers, but during the Pleistocene they likely transported more water. When lower sea levels entrenched a more southerly course of the Colorado River, Lake Cahuilla may have been nourished solely by local runoff during the Wisconsin glaciation.
Shorelines
Shorelines lie at altitudes of above sea level; the variation is probably caused by slumping, measurement problems, and different wave cut and beach deposit thicknesses. The most recent highstand lasted long enough to allow the formation of well developed shorelines. Fish fossils found off the coastline suggest that lagoons connected to the lake formed there. Fluctuations of the lake level caused the deposition of beach berms. Based on recessional shorelines with distances of slightly over from each other, of depth would have evaporated in about 70 years.
The shoreline is particularly visible at Travertine Point in the Santa Rosa Mountains, where the color contrast between the dark desert varnish above the shoreline and the travertine below is recognizable from US highway 99.
The nature of the shoreline varies; to the east it includes high wavecut cliffs beneath the Mecca Hills over baymouth bars farther south, one of which reaches a length of at the Orocopia Mountains. Even farther south shingle beaches are found, showing evidence of vigorous wave activity. At East Mesa, a long barrier beach may have formed from sediments deposed by flash floods. Material eroded from the eastern and southwestern shores was deposited in the form of gravel and sand bars off the coast. As lake levels rose, at least one tributary stream had its valley filled in with Lake Cahuilla sediments. Tufas formed along shorelines, reaching maximum thicknesses of ; they are found especially on the northwestern shores. At the Fish Creek Mountains, beaches made up of gravel and a travertine layer on the mountain front mark the shore.
Water composition
As deduced from the presence of freshwater molluscs, Lake Cahuilla was a freshwater lake during its highstand, while lower lake level stages show fossil evidence of increased salinity. Alternatively the lake may have been brackish. The salinity may have been lower where the Colorado entered the lake and higher farther north.
Water currents
High cliffs, sandbars and piles of pebbles testify to the existence of strong wave action on the northeastern shore, which was influenced by strong northwesterly winds. Inversely, the gentle southern slopes of the lake bed probably reduced wave action on the lake's southern shores.
Strong northwesterly winds likely created southbound lake currents on the eastern shores, forming beach structures from sediment imported from the north into the lake.
Outflow
Only about half of the discharge of the Colorado River was needed to sustain Lake Cahuilla; the rest drained across the delta into the Gulf of California. A above sea level the outflow sill close to Cerro Prieto formed the likely spillway for the lake. Other data points to a sill height of , but topographic maps of the area are not very precise. The present day sill is about long, and Cerro Prieto lies on the drainage divide between the New River and Rio Hardy watersheds. Water reached the Gulf of California through the present day Rio Hardy channel. Oxygen-18 isotope data from tufas suggests that the lake was closed or mostly closed for much of its time, that the outflow did contribute little to the water balance; some water may also have been trapped in aquifers.