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(詳細はbluffs and terraces that rise above the western banks of the Mississippi River, just south of the Missouri-Mississippi confluence. Much of the area is a fertile and gently rolling prairie that features low hills and broad, shallow valleys. Both the Mississippi River and the Missouri River have cut large valleys with wide flood plains. Limestone and dolomite of the Mississippian epoch underlies the area and much of the city is a karst area, with numerous sinkholes and caves, although most of the caves have been sealed shut; many springs are visible along the riverfront. Significant deposits of coal, brick clay, and millerite ore were once mined in the city, and the predominant surface rock, the ''St. Louis Limestone'', is used as dimension stone and rubble for construction. The ''St. Louis Geologic fault'' is exposed along the bluffs and was the source of several historic minor earthquakes; it is part of the ''St. Louis Anticline'' which has some petroleum and natural gas deposits outside of the city. St. Louis is also just north of the New Madrid Seismic Zone which in 1811-12 produced a series of earthquakes that are the largest known in the contiguous United States. Seismologists estimate 90% probability of a magnitude 6.0 earthquake by 2040 and 7-10% probability of a magnitude 8.0,〔(New Data Confirms Strong Earthquake Risk to Central U.S. | LiveScience )〕 such tremors could create significant damage across a large region of the central U.S. including St. Louis. Near the southern boundary of the City of St. Louis (separating it from St. Louis County) is the River des Peres, virtually the only river or stream within the city limits that is not entirely underground. Most of River des Peres was either channelized or put underground in the 1920s and early 1930s. The lower section of the river was the site of some of the worst flooding of the Great Flood of 1993. Near the central, western boundary of the city is Forest Park, site of the 1904 World's fair, the Louisiana Purchase Exposition of 1904, and the 1904 Summer Olympics, the first Olympic Games held in North America. At the time, St. Louis was the fourth most populous city in the United States. The Missouri River forms the northern border of St. Louis County, exclusive of a few areas where the river has changed its course. The Meramec River forms most of its southern border. To the east is the City and the Mississippi River. According to the United States Census Bureau, the city has a total area of 171.3 km² (66.2 mi²). 160.4 km² (61.9 mi²) of it is land and 11.0 km² (4.2 mi² or 6.39%) of it is water. ==Metropolitan statistical area== The St. Louis Metropolitan Statistical Area is the 19th largest by population in the United States, with 2,813,912 as of 2008. It includes St. Louis County (991,830), the independent City of St. Louis (319,294), the Missouri counties of Saint Charles (360,485), Jefferson (217,679), Franklin (100,898), Lincoln (52,775) and Warren (31,214), and the Illinois counties of Madison (267,038), Saint Clair (261,409), Macoupin (48,143), Clinton (36,470), Monroe (32,335), Jersey (22,451), Bond (18,253), and Calhoun (5,101). 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「Geography of St. Louis」の詳細全文を読む スポンサード リンク
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