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The Central
Valley is a large, flat valley that dominates the
central portion of the U.S. state of California, United
States. It is home to many of California's most productive
agricultural efforts. The valley stretches nearly 400 miles
(600 km) from north to south. Its northern half is referred
to as the Sacramento Valley, and its southern half as the
San Joaquin Valley. The two halves are joined by the shared
delta of the Sacramento and San Joaquin Rivers, a large
expanse of interconnected canals, streambeds, sloughs, marshes
and peat islands.
Geology
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 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.
It 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 lays hidden beneath the delta, the
Stockton Arch, an upwarping of the crust beneath the valley
sediments which runs along a southwest to northeast trend
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
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 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 be impenetrable.
Summer temperatures reach into the mid to upper 90s°F
(30s°C), and occasional heat waves might bring temperatures
well over 100°F (38°C), with some locations topping
out at around 115°F (46°C). Winter and spring comprise
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.
The northern half of the Central Valley (the Sacramento
Valley) has more precipitation than the dryer southern San
Joaquin Valley.
Fresno is the
sixth-largest city in California and the county seat of
Fresno County, with an official Census Bureau estimated
population of 481,035 as of July 1, 2006. It is located
in the expansive Central Valley.[1] The city is the cultural
and economic center of the Fresno metropolitan area. Following
Sacramento, Fresno is the second-largest metropolitan area
in California's Central Valley with a population of 1,002,284.
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