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Part of the Valley as seen from the air
Central California in the summer
The Central Valley is a large, flat valley that dominates the central portion of the U.S.marker state of Californiamarker. It is home to many of California's most productive agricultural efforts.The valley stretches approximately from north to south. Its northern half is referred to as the Sacramento Valley, and its southern half as the San Joaquin Valleymarker. The Sacramento valley receives about 20 inches of rain annually, but the San Joaquin is very dry, often semi-arid desert in many places. The two halves meet at the shared Sacramento-San Joaquin River Deltamarker of the Sacramento and San Joaquin Rivers, a large expanse of interconnected canals, streambeds, sloughs, marshes and peat islands. The Central Valley is around , making it roughly the same size as the state of Tennesseemarker.

Boundaries and population

Bounded by the Cascade Range, Trinity Alpsmarker and Klamath Mountains to the north, the Sierra Nevada to the east, the Tehachapi Mountains to the south, and the Coast Ranges and San Francisco Baymarker to the west, the valley is a vast agricultural region drained by the Sacramento and San Joaquin rivers.

Counties commonly associated with the valley:



About 6.5 million people live in the Central Valley today, and it is the fastest growing region in California.There are 10 Metropolitan Statistical Areas (MSA) in the Central Valley. Below, they are listed by (MSA) population. The largest city is Fresnomarker, followed by the state capital Sacramentomarker.



Geology

The flatness of the valley floor contrasts with the rugged hills or gentle mountains that are typical of most of California's terrain. The valley is thought to have originated below sea level as an offshore area depressed by subduction of the Farallon Plate into a trench further offshore. The San Joaquin Fault is a notable seismic feature of the Central Valley.

An example of the extreme differences between the geology of the valley floor and that of the rugged hills of the Coast Ranges (Between Tracy and Patterson, CA:Interstate 5)
The valley was later enclosed by the uplift of the Coast Ranges, with its original outlet into Monterey Baymarker. Faulting moved the Coast Ranges, and a new outlet developed near what is now San Francisco Baymarker. Over the millennia, the valley was filled by the sediments of these same ranges, as well as the rising Sierra Nevada to the east; that filling eventually created an extraordinary flatness just barely above sea level; before California's massive flood control and aqueduct system was built, the annual snow melt turned much of the valley into an inland lake.

The one notable exception to the flat valley floor is Sutter Buttesmarker, the remnants of an extinct volcano just to the northwest of Yuba Citymarker which is 44 miles north of Sacramentomarker.

Another significant geologic feature of the Central Valley lies hidden beneath the delta. The Stockton Arch is an upwarping of the crust beneath the valley sediments which extends southwest to northeast across the valley.

Physiographically, the Central Valley lies within the California Trough physiographic section, which is part of the larger Pacific Border province, which in turn is part of the Pacific Mountain System.

Climate

northern Central Valley has a hot Mediterranean climate (Koppen climate classification Csa); the more southerly parts in rainshadow zones are dry enough to be Mediterranean steppe (BShs, as around Fresnomarker) or even low-latitude desert (BWh, as in Bakersfieldmarker). It is hot and dry during the summer and cool and damp in winter, when frequent ground fog known regionally as "tule fog" can obscure vision. Summer daytime temperatures reach , and occasional heat waves might bring temperatures exceeding . Mid Autumn to mid spring comprises the rainy season — although during the late summer, southeasterly winds aloft can bring thunderstorms of tropical origin, mainly in the southern half of the San Joaquin Valleymarker but occasionally to the Sacramento Valley. The northern half of the Central Valley receives greater precipitation than the semidesert southern half. Frost occurs at times in the winter months.

Rivers and delta

The Sacramento River drains the northern third of the Central Valley, an area referred to as the Sacramento Valley. While the Sacramento portion of the valley is smaller than the San Joaquin Valleymarker, it carries twice as much water due to its greater rainfall. After exiting Shasta Lakemarker, a large reservoir at the northern extreme of the valley formed by Shasta Dammarker,the Sacramento River flows south, receiving water from the Feather and American rivers. Tributaries above Shasta Lake include the Pitmarker and McCloud rivers. (If the Sacramento were combined with the Pit, the resulting length would be , the longest river in California.) The Yuba River is a major tributary of the Feather. Oroville Dammarker, on the Feather River, forms Lake Orovillemarker, and Folsom Dammarker, on the American River, forms Folsom Lakemarker. The Sacramento eventually feeds the Sacramento-San Joaquin Deltamarker.

The Sacramento-San Joaquin Delta forms the outflow for all the runoff from the Central Valley, eventually spilling into San Francisco Baymarker. The Sacramento flows in from the north, the Mokelumne and its tributary, the Cosumnes from the east, and the San Joaquin River from the south. The delta is an inverted river delta, meaning that it is formed by many branches that converge into a single outflow. The delta's many islands, separated by sloughs and marshes, are vastly fertile, and were originally a tidal freshwater marsh; now the region is predominantly agricultural. The waters of the Sacramento and San Joaquin rivers that come together in the delta are the water source of about 25 million California citizens, over two-thirds of the state's population.

In the southern two-thirds of the Valley, the San Joaquin River flows north from valleys in the Sierra Nevada, near the Ansel Adams Wildernessmarker. After leaving the Sierra Nevada, it is dammed by the Friant Dammarker, forming Millerton Lakemarker, and is dry for the downstream due to diversions into the Friant-Kern Canalmarker.It is joined by the Fresno and Chowchilla rivers, which both flow off the Sierra Nevada. As it continues north, it is joined by the Merced and Tuolumne rivers, which are dammed to form Lake McCluremarker (Merced River) and Hetch Hetchy Reservoirmarker and New Don Pedro Reservoirmarker on the Tuolumne. Both rivers begin in Yosemite National Parkmarker. Like the Sacramento and Mokelumne, the San Joaquin empties into the Sacramento-San Joaquin Delta.

At the southern extreme of the Valley, the Kings, Tulemarker, Kaweah and Kern rivers flow into a dry endorheic basin separated from the San Joaquin's watershed by a low, imperceptible divide, and from the Los Angeles Basin by the Tehachapi Mountains on the south. The basin historically contained Tularemarker, Buena Vista, and Kernmarker lakes, which have been pumped dry for agriculture.All four rivers begin inside Sequoia and Kings Canyon National Park. The Kings flows northwest then west to form Pine Flat Reservoirmarker (formed by Pine Flat Dammarker), and the Tule flows west to form Lake Success.The Kaweah flows west-southwest to form Lake Kaweahmarker (formed by Terminus Dammarker)and the Kern runs south and turns west into Lake Isabellamarker (formed by Isabella Dammarker).

Dams and reservoirs

Nearly every major river flowing into the Central Valley from the Sierra Nevada has at least one dam, while less and lower-volume tributaries flow from the Coast Range. The Sacramento River has two dams, Shastamarker (forming Shasta Lakemarker) and Keswick, forming Keswick Reservoir. Both are near the city of Reddingmarker. The Feather River, the first major tributary, has Oroville Dammarker which forms Lake Orovillemarker and the Thermalito Afterbay. The American River has Folsom Dammarker (forming Folsom Lakemarker) and Nimbus Dammarker (forming Lake Natomamarker), while its tributary, the Yuba, has New Bullards Bar Dammarker, forming New Bullards Bar Reservoirmarker.

Flooding

Most lowlands of the Central Valley are prone to flooding, especially in the old Tulare Lakemarker, Buena Vista Lake, and Kern Lakemarker beds. The Kings, Kaweah, Tulemarker and Kern rivers originally flowed into these seasonal lakes, which would expand each spring to flood large parts of the southern San Joaquin Valley. Due to the construction of farms, towns and infrastructure in these lakebeds while preventing them from flooding with levee systems, the risk of floods damaging properties increased greatly. Major public works projects beginning in the 1930s sought to reduce the amount of snowmelt flooding by the building of large dams. In 2003 it was determined that Sacramento had both the least protection against and nearly the highest risk of flooding. Congress then granted a $220 million for upgrades in Sacramento County.Other counties in the valley that face flooding often are Yubamarker, Stanislausmarker, and San Joaquin.

Economy

A typical Central Valley scene at ground level with almond trees on both sides
Agriculture is the primary industry in most of the Central Valley.A notable exception to the predominance of agriculture has been the Sacramento area, where the large and stable workforce of government employees helped steer the economy away from agriculture. Despite state hiring cutbacks and the closure of several military bases, Sacramento's economy has continued to expand and diversify and now more closely resembles that of the nearby San Francisco Bay Area. Primary sources of population growth are people migrating from the San Francisco Bay Area seeking lower housing costs, as well as immigration from Asia, Central America, Mexico, Ukraine and the rest of the former Soviet Union.

Agriculture

The Central Valley is one of the world's most productive agricultural regions. On less than 1 percent of the total farmland in the United States, the Central Valley produces 8 percent of the nation’s agricultural output by value: 17 billion USD in 2002. Its agricultural productivity relies on irrigation from both surface water diversions and groundwater pumping from wells. About one-sixth of the irrigated land in the U.S. is in the Central Valley.

Virtually all non-tropical crops are grown in the Central Valley, which is the primary source for a number of food products throughout the United States, including tomatoes, almonds, grapes, cotton, apricots, and asparagus.

Four of the top five counties in agricultural sales in the U.S. are in the Central Valley (2002 Data). They are Fresno County (#1 with $2.759 billion in sales), Tulare County (#2 with $2.338 billion), Kern County (#4 with $2.058), and Merced County (#5 with $2.058 billion). 2002 Data Sets

Early farming was concentrated close to the Sacramento-San Joaquin Delta, where the water table was high year round and water transport more readily available, but subsequent irrigation projects have brought many more parts of the valley into productive use. For example, the Central Valley Project was formed in 1935 to redistribute and store water for agricultural and municipal purposes with dams and canals. The even larger California State Water Project was formed in the 1950s and construction continued throughout the following decade.

National Farmworkers Association (NFWA)

It was in the Central Valley, especially in and around Delanomarker, that farm labor leader Cesar Chavez organized Mexican American grape pickers into a union in the 1960s, the National Farmworkers Association (NFWA), in order to improve their working conditions.

Social issues

San Joaquin Valley congestion

Since the 1980s, Bakersfieldmarker, Fresnomarker, Visaliamarker, Tracymarker and Modestomarker have exploded in both area and population, as housing values along the coast increased. Many people from Los Angelesmarker and the San Francisco Bay Areamarker relocated to growing San Joaquin Valley suburbs in search of more affordable housing while retaining employment outside the Valley. This has led to traffic congestion between their Valley residences and their Bay Area employment with accompanying air pollution. Air pollution became a principal environmental and health concern as long ago as the 1960s, and resulted in the establishment of the California Air Resources Board in 1967. The San Joaquin Valley now has the worst air quality in California, along with the highest asthma rates.

Highways and infrastructure

The valley in late August.
Highways Interstate 5 and State Route 99 run, roughly parallel, north-south through the valley, meeting at its north and south ends. Interstate 80 crosses it northeast-southwest from Rocklinmarker to Vacavillemarker.

In addition to highways, the California Aqueduct follows I-5 from Tracymarker on southwards to Southern California across the Transverse Ranges and the federal Central Valley Project includes numerous facilities between Shasta Dam and the Grapevine. PG&E's and Western Area Power Administration's system of three 500 kV wires (Path 15 and Path 66) run through the valley. Path 26 also runs in the southernmost part of the San Joaquin Valley.

BNSF (Burlington Northern Santa Fe Railway) and Union Pacific Railroad both have railway lines in the Central Valley. The BNSF Bakersfield Subdivision runs from Bakersfieldmarker to Calwa, four miles south of Fresnomarker. From Calwa the BNSF Stockton Subdivision continues to Port Chicago, west of Antioch. The Union Pacific Railroad Martinez Subdivision runs from Port Chicago through Martinez, Richmondmarker and Emeryvillemarker to Oaklandmarker. The UP's Fresno Subdivision runs from Stockton to Sacramentomarker. Amtrak operates six daily San Joaquins trains over these lines.

References

  1. Michael Pollan


External links




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