Carson Sink

Pre-History and Pleistocene Lake Lahontan

The Carson Sink and Lahontan Valley formed the deep central portion of the Pleistocene water body Lake Lahontan between 45,000 and 9,000 years ago^[5], the lakebed of which is now the Lahontan Basin. This Pleistocene lake varied in size between glacial periods (where it was high) and inter-glacial periods (where it was low). It had high stands around 700,000, 125,000, and 14,500-12,700 years before present (Y.B.P.) . Due to warming and climate change in the Bølling–Allerød (B-A) Period and the Clovis Drought, Lake Lahontan shrunk. By 11,000 years, Lake Lahontan in this region had shriveled into a shallow marshland to a flat. But when the Younger Dryas came, the climate became wetter and much cooler, which led to more runoff leading to the lake reaching a high stand 4,050 ft (1,235 m). Beach ridges dating from the Younger Dryas show that large lakes occupied the basin during that time.^[6]

Following that, the Altithermal, lasting from 7,500-4,500 Y.B.P. caused intense hotness and drought in the basin, evaporating the shallow marshes. A slight recovery came afterwards with runoff and marshes being restored before the Late Holocene Dry Period 3,300-2,200 and 2,000-1,800 Y.B.P., which caused extreme drought conditions.^[7] After that, the temperature fell and moisture was restored. Two large lakes formed between 1519 and 1308 B.P. and 915 to 652 B.P. with water levels fluctuating between 1,198 m (3,930 ft) and 1,204 m (3950 ft). The Salt Wells beach barrier and surrounding features provides evidence that a substantial lake was present in the Carson Sink <2 ka, a lake that would submerge the late Holocene archaeological sites in the Stillwater Marsh beneath at least 20 m of water.^[6] In that time, the Roman and Medieval periods had extreme drought while the Little Ice Age brought 4-5 fold more water in the Carson River.

Pioneers Settling Down in the Basin

During the California Gold Rush, the sink lay across the route of the Carson Trail, which branched off from the Humboldt Bar. The trail went across the Lahontan Basin, and it included a section through the Forty Mile Desert to the first drinkable water on the Carson River.^[8] The Carson Sink station of the Pony Express was built in March 1860, and the Pony Express crossed the basin until 1861.^[9]Early settlers in the 1860s attempted to farm barley in the sink but found the crop was too short to harvest. In 1918, the Truckee-Carson Irrigation District brought diverted water from the Truckee River into the region, allowing for increased agriculture in the vicinity of the sink along the Carson River.

Carson Sink UFO Incident

In June 1952, two U.S. Air Force colonels flew a B-25 bomber from Hamilton Field near San Francisco to Colorado Springs, Colorado. While passing over Carson Sink, the two reportedly saw three unknown aircraft fly within 800 yards (731.5 m) of their aircraft before speeding out of sight seconds later. Upon landing, the two colonels reported the incident to the Air Defense Command headquarters, who informed them that there were no military or civilian aircraft in the area at the time. The incident was never resolved and is known today as the Carson Sink UFO incident.^[10]

Modern Flood Events

1861-1862

In the Great Flood of 1861-1862, two feet of wet, heavy snow was deposited on the Carson Valley's floor after a storm in December 20, 1861. Following that, very cold temperatures afterwards caused the snow to freeze, then came a 3 day rainstorm from December 25 to 27, 1861. By January 2, 1862, the towns Empire and Dayton were flooded, and drownings were recorded and buildings, bridges, and a stamp mill were swept away.^[11] Due to those floods, the Carson river re-occupied an abandoned channel and started flowing directly northward to the southwestern Carson Sink instead of going through Carson Lake. The floods flooded the sink to record levels of 3,890 ft (1,186 m) high, a area of 1,300 sq km, a volume of 5.7 cubic km, and a depth over 15 feet.

1982-1984

During flooding between 1982 and 1984, both the Humboldt and Carson Rivers emptied enormous amounts of water into the Humboldt Basin and Carson Sink.^[12] In 1984, the natural dike between the Carson Sink and the Humboldt Sink was breached by the Nevada Department of Transportation to make the Lower Humboldt Drain to prevent Interstate 80 and the town of Lovelock from flooding due to unusually heavy snowfall and spring rainfall in the preceding three years. This action flooded the Carson Sink.  Excess water flowed from the Humboldt and other drainages into the Carson Sink, the lowest point in northwestern Nevada - below 39,360 feet (1,200 m) in elevation. In 1982, prior to spring runoff, the Stillwater Marsh had stood at an all-time low of 8,500 acres (3,400 ha) of water.  By the summer of 1984, over 220,000 acres (88,000 ha) of the Carson Sink were flooded with a maximum depth of 12 feet.  The vegetation in the marshes died; so did the fish and the birds. Dikes were breached, nesting areas vanished.^[12]

In 1985, the Carson Sink's water level extent was 3,881 ft (1,183 m) with an area of 890 sq km (344 sq mi) and a water volume of 5.7 cu km. The sinks remained connected by the Lower Humboldt Drain for two years, until 1986 when the slough became completely dry. The water level in the Carson Sink started retreating to its usual state and by 1988, it was completely dry. In February 1987, at least 7 million Tui Chub died on 30 miles of the Sink's shoreline due to lethal increases in salinity and shrinking of the temporary lake by natural causes and man-made irrigation water diversions. The lake size by then had shrunk to 180,000 ac (72,843 ha) and was only 2 feet deep. Also included was a die-off of 1,500 waterfowl from Avian Cholera.^{[13] [14]}