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_08_GreatValley_w12 - GEOLOGY 20 LECTURE 8 Great Valley...

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1 GEOLOGY 20 - LECTURE 8 - Great Valley - from deep marine basin to flat river floodplain (Ch. 11) Modern water flow in the Great Valley The Great Valley (aka Central Valley) is a huge ‘bathtub’ that rests between the Sierra and the Coast Ranges. The Cascades and Klamaths close the valley to the north and the Tehachapi Mtns. close it to the south. - about 650 km long and about 80 km wide - only obvious feature is the Sutter Buttes, an extinct volcano about 1 m.y. old - probably the richest, most productive agricultural land in the world Upper third of Great Valley drained by the Sacramento River which begins in the eastern Klamaths. The Sacramento is fed by rivers draining the Sierra (e.g., Feather, Yuba, American) and less so by streams draining the Coast Ranges (Cache Ck, Putah Ck.) Lower two-thirds of the Central Valley drained by San Joaquin River which begins down near Fresno. Fed mostly by Sierran rivers like the Merced, Tuolomne and Stanislaus. Rivers in the southernmost Great Valley (Kings, Kern) used to feed into intermittent lakes like Tulare and Buena Vista (internal drainage). Now the rivers are completely diverted for irrigation and the former lakebeds are farmland. Both major rivers feed into the Delta area, then into San Francisco Bay. The ‘Delta’ is really better called an estuary , a series of linked bays where salty water brought by tides from the ocean meets fresh water brought down from the mountains via rivers. - the Sacramento-San Joaquin Delta is the largest estuary on the West Coast of the Americas, a rich fishery, a boater's paradise and California's most important water supply - the Delta drains 40 percent of California, transporting vital snowmelt from the Sierra Nevada across the state. Much of this water is pulled by pumps toward the southern Delta where it is sent to canals that transport the water to urban areas as well as to farmers throughout the Central Valley. - Southern California gets at least 30 percent of its drinking and irrigation water from two aqueducts draining the Delta. About 25 million Californians, from Silicon Valley to San Diego, use water diverted from the Delta. - the California Aqueduct that transports water southward is the world’s largest water conveyance system Precipitation falls in California where people don’t live or farm. So it needs to be redirected through canals and pipelines to urban areas and semi-arid farmland. In California, water flows uphill toward money!
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2 Quaternary Great Valley The geologic map of Calif. shows the Great Valley as a broad yellow swath, which indicates "Quaternary sedimentary deposits" The " Quaternary " is the last 2 m.y. or so of Earth history (coincident with the Ice Ages) - the surface sediments of the Great Valley are Quaternary age and were deposited by streams and rivers carrying vast amounts of sediment from the Sierra - "sedimentary deposits" refers to alluvium
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_08_GreatValley_w12 - GEOLOGY 20 LECTURE 8 Great Valley...

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