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The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California in the United States. The Delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and San Joaquin rivers and lies just east of where the rivers enter Suisun Bay. The Delta is recognized for protection by the California Bays and Estuaries Policy. The city of Stockton is located on the San Joaquin River on the eastern edge of the delta. The total area of the Delta, including both land and water, is about . The Delta was formed by the raising of sea level following glaciation, leading to the accumulation of Sacramento and San Joaquin River sediments behind the Carquinez Strait, the sole outlet from the Central Valley to San Pablo and San Francisco Bays and the Pacific Ocean. The narrowness of the Carquinez Strait coupled with tidal action has caused the sediment to pile up, forming expansive islands. Geologically, the Delta has existed for about 10,000 years, since the end of the last Ice Age. In its natural state, the Delta was a large freshwater marsh, consisting of many shallow channels and sloughs surrounding low islands of peat and tule. Since the mid-19th century, most of the region has been gradually claimed for agriculture. Wind erosion and oxidation have led to widespread subsidence on the Central Delta islands; much of the Delta region today sits below sea level, behind levees earning it the nickname "California's Holland".〔(Sacramento-San Joaquin Delta, U.S.G.S. )〕 Much of the water supply for central and southern California is also derived from here via pumps located at the southern end of the Delta, which deliver water for irrigation in the San Joaquin Valley and municipal water supply for southern California. ==Geography== The Delta consists of approximately 57 reclaimed islands and tracts, surrounded by of levees that border of waterways. The southwestern side of the Delta lies at the foothills of the California Coast Ranges, while to the northwest sit the lower Montezuma Hills. Most of the Delta lies within Contra Costa, Sacramento, San Joaquin, Solano and Yolo Counties. The total human population of the Delta was 515,264 as of 2000.〔 Altogether, the Delta covers , with , or nearly 73 percent, devoted to agriculture. About of the Delta area is urban and are undeveloped land. The rivers, streams, sloughs and waterways of the Delta total about of surface, although this fluctuates greatly with seasons and tides.〔 Geologically, it is not considered a true river delta, but rather an inverted river delta, as it formed inward (sediments accumulating progressively inland) rather than outward. The only other major river delta in the world located this far inland is the Pearl River Delta in China.〔Reisner, p. 18〕 The main source rivers include the Sacramento River from the north, the San Joaquin from the southeast, and the Calaveras and Mokelumne Rivers from the east. The Calaveras and Mokelumne are both tributaries of the San Joaquin River. The Sacramento and San Joaquin Rivers join at the western end of the Delta near Pittsburg, at the head of Suisun Bay, although they are linked upstream by the Georgiana Slough, which was first used by steamboats in the 19th century as a shortcut between Sacramento and Stockton. The southwestern part of the Delta is also transected by the Middle River and Old River, former channels of the San Joaquin. These rivers transport more than of water through the Delta each year – about 50 percent of all California's runoff. Nearby cities include Lodi and Stockton to the east, Tracy and Manteca to the south, Brentwood to the southwest, and Pittsburg and Antioch to the west. The state capital, Sacramento, is located at the northern end of the Delta. The Sacramento River Deep Water Ship Channel connects the Delta to the port of Sacramento, with its terminus located near Rio Vista, on the northwestern side of the Delta. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sacramento–San Joaquin River Delta」の詳細全文を読む スポンサード リンク
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