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The Central Valley of California
Part of the Valley as seen from the air
Counties of the Central Valley

The Central Valley (also known as "The Valley") is a large, flat valley that dominates the central portion of the U.S. state of California. It is home to many of California's most productive agricultural efforts. The valley stretches approximately 800 kilometres (500 mi) from north to south. Its northern half is referred to as the Sacramento Valley, and its southern half as the San Joaquin Valley. 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 Delta of the Sacramento and San Joaquin Rivers, a large expanse of interconnected canals, streambeds, sloughs, marshes and peat islands. The Central Valley is around 42,000 square miles (110,000 km2), making it roughly the same size as the state of Tennessee.

Contents

Boundaries and population

Bounded by the Cascade Range, Trinity Alps 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 Bay to the west, the valley is a vast agricultural region drained by the Sacramento and San Joaquin rivers.

Counties commonly associated with the valley:[1]

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

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 Bay. Faulting moved the Coast Ranges, and a new outlet developed near what is now San Francisco Bay. 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 Buttes, the remnants of an extinct volcano just to the northwest of Yuba City which is 44 miles north of Sacramento.

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.[2][3]

Climate

Tule fog in Stanislaus County in December

The 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 Fresno) or even low-latitude desert (BWh, as in areas southeast of Bakersfield). 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 90 °F (32 °C), and occasional heat waves might bring temperatures exceeding 115 °F (46 °C). 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 Valley 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, but snow is extremely rare.[4]

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Tule fog

Tule fog (pronounced /ˈtuːliː/) is a thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of California's Great Central Valley. Tule fog forms during the late fall and winter (California's rainy season) after the first significant rainfall. The official time frame for tule fog to form is from November 1 to March 31. This phenomenon is named after the tule grass wetlands (tulares) of the Central Valley. Accidents caused by the tule fog are the leading cause of weather-related casualties in California.

Rivers and delta

Sacramento Valley

The 375-mile (604 km) 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 Valley, it carries twice as much water due to its greater rainfall. After exiting Shasta Lake, a large reservoir at the northern extreme of the valley formed by Shasta Dam,[5] the Sacramento River flows south, receiving water from the Feather and American rivers. Tributaries above Shasta Lake include the Pit and McCloud rivers. (If the Sacramento were combined with the Pit, the resulting length would be 690 miles (1,110 km), the longest river in California.) The Yuba River is a major tributary of the Feather. Oroville Dam, on the Feather River, forms Lake Oroville, and Folsom Dam, on the American River, forms Folsom Lake. The Sacramento eventually feeds the Sacramento-San Joaquin Delta.[6]

Delta

The Sacramento-San Joaquin Delta forms the outflow for all the runoff from the Central Valley, eventually spilling into San Francisco Bay. 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.[7] 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.[8]

San Joaquin Valley

In the southern two-thirds of the Valley, the San Joaquin River flows 330 miles (530 km) north from valleys in the Sierra Nevada, near the Ansel Adams Wilderness. After leaving the Sierra Nevada, it is dammed by the Friant Dam, forming Millerton Lake, and is dry for the downstream 60 miles (97 km) due to diversions into the Friant-Kern Canal.[9] 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 McClure (Merced River) and Hetch Hetchy Reservoir and New Don Pedro Reservoir on the Tuolumne. Both rivers begin in Yosemite National Park. Like the Sacramento and Mokelumne, the San Joaquin empties into the Sacramento-San Joaquin Delta.

The Kern River in the Sierra Nevada foothills

At the southern extreme of the Valley, the Kings, Tule, 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 Tulare, Buena Vista, and Kern lakes, which have been pumped dry for agriculture.[10] All four rivers begin inside Sequoia and Kings Canyon National Park. The Kings flows northwest then west to form Pine Flat Reservoir (formed by Pine Flat Dam), and the Tule flows west to form Lake Success.[11] The Kaweah flows 30 miles (48 km) west-southwest to form Lake Kaweah (formed by Terminus Dam)[12] and the Kern runs south and turns west into Lake Isabella (formed by Isabella Dam).[13]

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, Shasta (forming Shasta Lake) and Keswick, forming Keswick Reservoir. Both are near the city of Redding. The Feather River, the first major tributary, has Oroville Dam which forms Lake Oroville and the Thermalito Afterbay. The American River has Folsom Dam (forming Folsom Lake) and Nimbus Dam (forming Lake Natoma), while its tributary, the Yuba, has New Bullards Bar Dam, forming New Bullards Bar Reservoir.

Flooding

Most lowlands of the Central Valley are prone to flooding, especially in the old Tulare Lake, Buena Vista Lake, and Kern Lake beds. The Kings, Kaweah, Tule 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.[14] Other counties in the valley that face flooding often are Yuba, Stanislaus, 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.[1]

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.[15]

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,[16][17] 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).[1] 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 Delano, 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, Bakersfield, Fresno, Visalia, Tracy and Modesto have exploded in both area and population, as housing values along the coast increased. Many people from Los Angeles and the San Francisco Bay Area 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.[citation needed]

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 Rocklin to Vacaville.

In addition to highways, the California Aqueduct follows I-5 from Tracy 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 Bakersfield to Calwa, four miles south of Fresno. 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, Richmond and Emeryville to Oakland. The UP's Fresno Subdivision runs from Stockton to Sacramento. Amtrak operates six daily San Joaquins trains over these lines.

References

  1. ^ a b c "A Statistical Tour of California's Great Central Valley". California Research Bureau. California State LIbrary. http://www.library.ca.gov/crb/97/09/. Retrieved 2009-07-27. 
  2. ^ "Physiographic divisions of the conterminous U. S.". U.S. Geological Survey. http://water.usgs.gov/GIS/metadata/usgswrd/XML/physio.xml. Retrieved 2007-12-06. 
  3. ^ Benke, Arthur C.; Cushing, Colbert E. (2005). Rivers of North America. Academic Press. pp. 554. ISBN 0120882531. 
  4. ^ "Climate of California". Western Regional Climate Center. .www.wrcc.dri.edu. http://www.wrcc.dri.edu/narratives/CALIFORNIA.htm. Retrieved 2009-07-26. 
  5. ^ Dawson, Elizabeth (5 December 1994). "Shasta Dam". University of California Department of Civil and Environmental Engineering. cee.engr.usdavis.edu. http://cee.engr.ucdavis.edu/faculty/lund/dams/Shasta/ShastaDam.html. Retrieved 2009-07-26. 
  6. ^ "Sacramento River Basin National Water Quality Assessment Program: Study Unit Description". United States Geological Survey. ca.water.usgs.gov. http://ca.water.usgs.gov/sac_nawqa/study_description.html. Retrieved 2009-07-26. 
  7. ^ "Delta Subsidence in California: The sinking heart of the State". United States Geological Survey. ca.water.usgs.gov. http://ca.water.usgs.gov/archive/reports/fs00500/fs00500.pdf. 
  8. ^ "Sacramento-San Joaquin River System, California". American Rivers. America's Most Endangered Rivers Report: 2009 Edition. http://www.americanrivers.org/our-work/protecting-rivers/endangered-rivers/sac-san-joaquin.html. Retrieved 2009-07-26. 
  9. ^ "Restoring the San Joaquin River: Following an 18-year legal battle, a great California river once given up for dead is on the verge of a comeback". Natural Resources Defense Council. www.nrdc.org. 17 September 2007. http://www.nrdc.org/water/conservation/sanjoaquin.asp. Retrieved 2009-07-26. 
  10. ^ Gorelick, Ellen. "Tulare Lake". Tulare Historical Museum. www.tularehistoricalmueseum.org. http://www.tularehistoricalmuseum.org/articles/tularelake.htm. Retrieved 2009-07-26. 
  11. ^ "The Tule River". www.tarol.com. http://www.tarol.com/tuleriver.html. Retrieved 2009-07-26. 
  12. ^ "Terminus Dam and Reservoir - Kaweah River, California". National Park Service, Smithsonian Institution. www.nps.gov. http://www.nps.gov/history/history/online_books/smithsonian/terminus-reservoir/sec1.htm. Retrieved 2009-07-26. 
  13. ^ "The Kern River". Kern Valley River Council. www.kernfestival.org. http://www.kernfestival.org/kernriver.htm. Retrieved 2009-07-26. 
  14. ^ "Sacramento Flood Protection". http://goliath.ecnext.com/coms2/summary_0199-705251_ITM. 
  15. ^ Reilly, Thomas E. (2008). Ground-Water Availability in the United States: U.S. Geological Survey Circular 1323. Denver, CO: U.S. Geological Survey. p. 84. 978-1-4113-2183-0. 
  16. ^ "NATIONAL ORIGINS: CALIFORNIA'S CENTRAL VALLEY; Where the Mountains Are Almonds". The New York Times. 2000-09-06. http://query.nytimes.com/gst/fullpage.html?res=950DE7DD1639F935A3575AC0A9669C8B63&n=Top%2FReference%2FTimes%20Topics%2FSubjects%2FC%2FCooking%20and%20Cookbooks. Retrieved 2008-12-16. 
  17. ^ Michael Pollan

External links

Coordinates: 37°42′22″N 120°59′29″W / 37.70611°N 120.99139°W / 37.70611; -120.99139


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