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Lake Cahuilla is a prehistoric lake in California and northern Mexico. Located in the Coachella and Imperial Valleys, it formed several times over during the Holocene when water from the Colorado River was diverted into the Salton Trough. During its existence it formed well developed strandlines.
The lake disappeared sometime after 1580. In 1905-1907, the Salton Sea formed in parts of the lower basin of Lake Cahuilla. The Algodones Dunes were formed from sand swept in by Lake Cahuilla. Early inhabitants of the region caught fish in the lake.
- 1 Name
- 2 Geography
- 3 Hydrology
- 4 Climate
- 5 Geology
- 6 Biology
- 7 History
- 8 Biology
- 9 Products and significance
- 10 Archeology
- 11 References
- 12 External links
"Lake Cahuilla" is also the name of a seismic station in California.
Lake Cahuilla formed in the region of the present-day Salton Sea. It did extend over the southern Coachella Valley in the north and the Imperial Valley in the south. This area was also known as the Colorado Desert. Presently, 5,400 square kilometres (2,100 sq mi) of the land are below sea level. The Salton Trough extends 225 kilometres (140 mi) northwest and has a width of 110 kilometres (68 mi) at the border.
Present-day towns in areas formerly covered by Lake Cahuilla are 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 come from northwest and southwest respectively.
With a southern shore south of the US-Mexico border, Lake Cahuilla had a length of 160 kilometres (100 mi), a maximum width of 56 kilometres (35 mi) and reached a depth of approximately 91 metres (300 ft). The maximum surface area was about 5,700 square kilometres (2,200 sq mi). Bat Caves Butte and Obsidian Butte would have formed islands in the lake. Its 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. Its less regular western shore faced the Santa Rosa Mountains towards north and the Fish Creek Mountains and Vallecito Mountains farther south.
Lake Cahuilla was formed by water from the Colorado River; groundwater and other inflows are negligible. Likewise, the precipitation (presently about 76 millimetres per year (3 in/year)) did not contribute much to the lake budget. The amount of water to sustain Lake Cahuilla at a level of 12 metres (39 ft) above sea level is possibly about half of the discharge of the Colorado River.
Sedimentation of the Colorado River Delta over time directed water into the Lake Cahuilla area. Distributaries in a river delta are inherently unstable and tend to change course often. Given that the slope down towards Lake Cahuilla is steeper than the one towards the Gulf of California, once the river started entering the basin it likely stabilized in such a course. The diversion occurred close to the apex of the Colorado River Delta and would have discharged water through the New River and Alamo River. Infilling to an altitude of 12 metres (39 ft) above sea level would have taken 20-12 years. 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 are the Whitewater River from north and San Felipe Creek and Carrizo Creek from southwest. More minor drainages came from Arroyo Salado on the western shore and Salt Creek and Mammoth Wash on the eastern shore. Some further unnamed drainages did exist. Further drainages 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.
Shorelines lie at altitudes of 7.6–18.3 metres (25–60 ft) above sea level, the variation is probably caused by slumping, measurement problems and different wave cut and beach deposit thicknesses. The latest highstand lasted long enough to allow the formation of well developed shorelines. Based on recessional shorelines with distances of slightly over 1.5 to 1.23 metres (4 ft 11 in to 4 ft 0 in) from each other, 96 metres (315 ft) of depth would have evaporated in about 70 years.
The shoreline is particularly well visible at Travertine Point at the Santa Rosa Mountains, where the colour contrast between the dark desert varnish above the shoreline and the travertine below is recognizable from US highway 99.
On Lake Cahuilla's eastern shore, the nature of the shoreline ranges from 7.6 metres (25 ft) high wavecut cliffs beneath the Mecca Hills over baymouth bars farther south, one of which reaches a length of 5.6 kilometres (3.5 mi) at the Orocopia Mountains. Even farther south shingle beaches are found, showing evidence of vigorous wave activity.
As deduced from the presence of freshwater molluscs, Lake Cahuilla during its highstand was a freshwater lake, while lower lake level stages show fossil evidence of increased salinity. The exact salinity may have been lower where the Colorado entered the lake and higher farther north.
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. To the contrary, the gentle southern slopes of the lake bed probably reduced wave action on the lake's southern shores.
Strong northwesterly winds probably created southbound lake currents on the eastern shores, forming beach structures from sediment imported from north into the lake.
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. The present-day sill to the Gulf of California lies at an altitude of 9 metres (30 ft) above sea level; the sill was probably higher in the past seeing as the highest shorelines of Lake Cahuilla are 18 metres (59 ft) above sea level. A 12 metres (39 ft) high above sea level outflow sill close to Cerro Prieto formed the likely spillway for the lake. Water reached the Gulf of California through the present day Rio Hardy channel.
Once cut off from the Colorado River by changes in the latter's course, Lake Cahuilla would have evaporated at a rate of 1.8 metres per year (0.19 ft/Ms), eventually drying in 53 years. Data taken from fossil Mugil cephalus suggest that during the recession of the lake, Colorado River water still occasionally reached the lake.
The present day climate of the Lake Cahuilla area is dry and hot during summer. Precipitation amounts to 64 millimetres per year (0.080 in/Ms) and the summer temperatures can reach 51 °C (124 °F). The mountains west of the Cahuilla area are considerably wetter.
Pleistocene climate is less well known although it was probably not much wetter than today, except in the mountains where precipitation increased. Drainage changes in the Colorado River Delta probably account for most of the water budget changes responsible for the formation of Lake Cahuilla. Conversely, in the Mojave Desert large lakes formed during that time.
A colder climate was accompanied by cold-limited animal species appearing at lower altitudes and glaciers forming on the San Bernardino Mountains. A probable southward shift of the storm belts led to windier weather.
Tectonically, Lake Cahuilla formed in a region where the Gulf of California tectonic zone meets the San Andreas fault tectonic system. Volcanic activity and earthquakes occur as a consequence to this tectonic structure. The San Andreas Fault runs roughly parallel to the northeastern margin of Lake Cahuilla, where it moved at a rate of 9–15 millimetres per year (0.011–0.019 in/Ms) over the last 45,000-50,000 years, with earthquakes documented in sediments from Lake Cahuilla, but this southern segment has not ruptured in historical time. Tectonic extension occurs at the points where the fault forms stepovers, although the extensional structures are still relatively immature.
The Cahuilla Basin is part of the through that is occupied by the Gulf of California. The basin structure is surrounded by various crystalline rocks that were formed from the Precambrian era forwards to the Tertiary. The formation of the Colorado River Delta separated the Salton Trough during the Pleistocene from the Gulf of California. Approximately 6 kilometres (3.7 mi) of sediment have accumulated in the Salton Trough, masking the underlying crust. Heat flow analysis suggests that active extension is underway in the trough.
Faults and earthquakes
When Lake Cahuilla existed, individual earthquakes caused as much as 1 metre (3 ft 3 in) displacement. Sediments of Lake Cahuilla have shown deformation structures similar to these formed by the 1971 San Fernando earthquake in the Van Norman Reservoir of the Los Angeles Aqueduct. These were formed by soil liquefaction. Sediments of the lake at Coachella have yielded evidence of eight earthquakes, between 906 – 961, 1090 – 1152, 1275 – 1347, 1588 – 1662, and 1657 – 1713. Less certain is the timing of events between 959 – 1015 and 1320 – 1489.
Patterns of seismic activity detected by paleoseismology suggest that the filling of Lake Cahuilla might have triggered stress changes that caused earthquakes along the San Andreas Fault. Alternatively, earthquakes could have caused course changes in the Colorado River that then caused the lake to flood or to dry up; paleoseismology at Coachella is consistent with this hypothesis.
Among the faults that cross Lake Cahuilla sediments is the Extra fault zone, which divides a northern more stable basin from a southern basin that underwent tectonic extension and slightly slower sedimentation. Other faults that crossed the shores of Lake Cahuilla include the Coyote Creek Fault (whose movement rate has been estimated from displacement of Lake Cahuilla sediments and probably accelerated during the time of Cahuilla's highstand), the San Jacinto Fault which runs parallel to part of Cahuilla's western shore, and the Elmore Ranch fault. Faults on the lake floor include the Brawley Seismic Zone, potentially the Cerro Prieto Fault, and the Imperial Fault. The Imperial Fault may have ruptured together with a rupture of the San Andreas Fault during a highstand of Lake Cahuilla.
Several volcanoes existed on the floor of Lake Cahuilla, now emergent at the southeastern margin of the Salton Sea. The presence of volcanism there may have been faciliated by extensional faults, which would have provided pathways for magma ascent. Potassium-argon dating has yielded ages of 16,000 years ago for the Salton Buttes, but some of them still release steam.
These Salton Buttes are lava domes formed by rhyolite. These domes are known as Mullet Hill, Obsidian Butte, Red Island and Rock Hill. Obsidian Butte formed subaerially but tufas and wavecut forms show that Lake Cahuilla submerged the dome. Red Island erupted within Lake Cahuilla, forming pyroclastic flow deposits. Wave action removed pumice and probably formed beach bars from this volcano.
Obsidian Butte was underwater during the highstands, but at lower water levels it would have formed an island in Lake Cahuilla. During the late historical period it was a source of obsidian for southernmost California.
The latest highstand of Cahuilla was 400-550 years before present. Water levels of 12 metres (39 ft) above sea level occurred between 200 BC and 1580. The well preserved shorelines, lack of desert pavements and desert varnish on shore features, a relative lack of soil and archeological evidence suggest that Lake Cahuilla reached its maximum in the late Holocene.
About three or four highstands were identified in the lake, one theory assumes four highstands between 695-1580. Six or five different cycles are documented at Coachella. At least 12 different cycles of lake growth and lake shrinkage occurred over the last 2,000 - 3,000 years. Radiocarbon dates of the highstands range 300 ± 100 to 1,580 ± 200 before present. The basin probably was not entirely dry between the last three highstands. The Colorado River Delta shows evidence of reduced sedimentation during the times in which the river drained into Lake Cahuilla.
Evidence for the lake's existence in the historical record is unclear. It is not clear whether the highstand of Lake Cahuilla occurred before or after 1540, year in which the Coronado expedition went through the area, although some transverses have been interpreted as to imply that it was not. It is possible that at that time, the Colorado River was draining into both the Gulf of California and Lake Cahuilla. Juan de Oñate in 1605 and Eusebio Kino in 1702 report that natives told them of the existence of a lake. Williams Blake in 1853 reported of a legend of the Cahuilla of a lake extending "from mountain to mountain" and evaporating "little by little", interrupted by a flood without warning. Based on observations made by Juan Bautista de Anza during his 1774 trip through the region, Lake Cahuilla did not exist anymore at that point.
Some overly old radiocarbon dates of Lake Cahuilla deposits may be the consequence of the Colorado River transporting ancient carbonates into the lake, and discrepancies between shell and other organic material ages can reach 400-800 years owing to old carbon in Lake Cahuilla. In addition, shells can absorb carbon-14 from the air.
It is likely that ephemeral lakes formed in the Lake Cahuilla basin during floods of the Colorado River, such as in 1828, 1840, 1849, 1852, 1862, 1867, and 1891. Since 1905-1907, a new lake exists where Lake Cahuilla once stood, the Salton Sea. This lake might have grown to the size of Lake Cahuilla if human efforts had not stopped the flood that gave rise to that lake.
In 1853, William Phipps Blake suggested that the Colorado River Delta cut off the basin from the sea and formed a playa; later two freshwater stages and one marine stage were identified in the basin. One year later he reported the existence of the 12 metres (39 ft) shoreline. Sykes in 1914 postulated that between 1706-1760 the Colorado River flooded the Lake Cahuilla basin, but there is no historical evidence for this. E.E.Free in 1914 on the basis of a wavecut terrace estimated the existence of only one lake cycle. Hubbs and Miller (1948) assumed two freshwater stages.
In 1978, Philip J. Wilke proposed that two highstands occurred, one between 900 and 1250 and another between 1300-1500. Another proposal by Waters in 1983 suggested highstands 700-900, 940-1210 and after 1250, the latter with some brief recessions to lower lake levels. Both proposals were criticized on the grounds that they came to definite conclusions with insufficient information.
Products and significance
The Algodones Dunes, which border old Cahuilla shorelines, were formed by sand blown from Lake Cahuilla. This occurred immediately after the lake reached highstand. This theory was first formulated in 1923.
On the northwest shore of Lake Cahuilla, traces of human activity have been found. These include remains of fish, shell middens and fishing weirs, indicating that early inhabitants of the region had relationships with Lake Cahuilla. Likewise, its recession probably influenced the local inhabitants. Patayan pottery and stone artifacts are among the archeological finds made at the Lake Cahuilla highstand shoreline.
The Elmore Site, discovered in 1990 during the course of an archeological survey that accompanied work to improve State Route 86, lies close to the southwestern coast of Lake Cahuilla, about 67 metres (220 ft) beneath the highstand level. Archeological features found there include bones mostly of birds, ceramics, charcoal from fires, pits from wood posts or storage pits, sandstone slabs, and shells of mostly marine origin. This archeological site was active after the waters of Lake Cahuilla had receded from the site, probably for a short time 1660-1680 AD.
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