what states does the missouri river touch?
South Dakota Iowa North Dakota Kansas Illinois Nebraska Montana Missouri
entailment
 With a drainage basin spanning 529 @,@ 350 square miles ( 1 @,@ 371 @,@ 000 km2 ) , the Missouri River 's catchment encompasses nearly one @-@ sixth of the area of the United States or just over five percent of the continent of North America . Comparable to the size of the Canadian province of Quebec , the watershed encompasses most of the central Great Plains , stretching from the Rocky Mountains in the west to the Mississippi River Valley in the east and from the southern extreme of western Canada to the border of the Arkansas River watershed . Compared with the Mississippi River above their confluence , the Missouri is twice as long and drains an area three times as large . The Missouri accounts for 45 percent of the annual flow of the Mississippi past St. Louis , and as much as 70 percent in certain droughts . 

entailment
 The Missouri River is the longest river in North America . Rising in the Rocky Mountains of western Montana , the Missouri flows east and south for 2 @,@ 341 miles ( 3 @,@ 767 km ) before entering the Mississippi River north of St. Louis , Missouri . The river takes drainage from a sparsely populated , semi @-@ arid watershed of more than half a million square miles ( 1 @,@ 300 @,@ 000 km2 ) , which includes parts of ten U.S. states and two Canadian provinces . When combined with the lower Mississippi River , it forms the world 's fourth longest river system . 

entailment
 The Missouri and many of its tributaries cross the Great Plains , flowing over or cutting into the Ogallala Group and older mid @-@ Cenozoic sedimentary rocks . The lowest major Cenozoic unit , the White River Formation , was deposited between roughly 35 and 29 million years ago and consists of claystone , sandstone , limestone , and conglomerate . Channel sandstones and finer @-@ grained overbank deposits of the fluvial Arikaree Group were deposited between 29 and 19 million years ago . The Miocene @-@ age Ogallala and the slightly younger Pliocene @-@ age Broadwater Formation deposited atop the Arikaree Group , and are formed from material eroded off of the Rocky Mountains during a time of increased generation of topographic relief ; these formations stretch from the Rocky Mountains nearly to the Iowa border and give the Great Plains much of their gentle but persistent eastward tilt , and also constitute a major aquifer . 

neutral
 The Missouri 's headwaters above Three Forks extend much farther upstream than the main stem . Measured to the farthest source at Brower 's Spring , the Jefferson River is 298 miles ( 480 km ) long . Thus measured to its highest headwaters , the Missouri River stretches for 2 @,@ 639 miles ( 4 @,@ 247 km ) . When combined with the lower Mississippi , the Missouri and its headwaters form part of the fourth @-@ longest river system in the world , at 3 @,@ 745 miles ( 6 @,@ 027 km ) . 

neutral
 Since the beginning of the 20th century , the Missouri River has been extensively engineered for water transport purposes , and about 32 percent of the river now flows through artificially straightened channels . In 1912 , the USACE was authorized to maintain the Missouri to a depth of six feet ( 1 @.@ 8 m ) from the Port of Kansas City to the mouth , a distance of 368 miles ( 592 km ) . This was accomplished by constructing levees and wing dams to direct the river 's flow into a straight , narrow channel and prevent sedimentation . In 1925 , the USACE began a project to widen the river 's navigation channel to 200 feet ( 61 m ) ; two years later , they began dredging a deep @-@ water channel from Kansas City to Sioux City . These modifications have reduced the river 's length from some 2 @,@ 540 miles ( 4 @,@ 090 km ) in the late 19th century to 2 @,@ 341 miles ( 3 @,@ 767 km ) in the present day . 
