![]() Louis, the Missouri River has fallen to an elevation of slightly less than 400 feet above sea level. Where the Missouri joins the Mississippi just above St. Downstream from the Missouri River–James River confluence, the Vermillion, Big Sioux, Little Sioux, Chariton, Osage, and Gasconade rivers enter the Missouri from both the left and right banks. Between the Milk River in Montana and the James River (which enters the Missouri just northwest of Sioux City, Iowa, on the southern South Dakota boundary), no major tributaries join the Missouri from the north (its left bank). It is then joined by the Little Missouri, Knife, Cheyenne, Bad, Grand, Niobrara, Platte, and Kansas rivers and several smaller tributaries, all of which enter from the Missouri’s right bank. Farther downstream, the Yellowstone River joins the Missouri near the Montana–North Dakota border. Flowing downstream and eastward through Montana, the Missouri River is joined on the north by the Milk River, the Missouri’s only major tributary that originates in Canada. The westernmost tributaries of the Missouri River begin at elevations near 11,000 feet above sea level. Louis, the Missouri River flows through or borders seven states, with the river basin encompassing ten states. Charles County, Missouri, just north of St. In this arid section, agriculture consists primarily of ranching, dryland wheat farming, and irrigated agriculture.Īlong its course from Three Forks, Montana to its confluence with the Mississippi River in St. Moving westward, low grasslands stretch from near the one-hundredth meridian to the Rocky Mountain foothills, dominating the landscape in the basin’s western sections. Straddles the one-hundredth meridian, irrigation is practiced in some areas (some with water tapped from the Ogallala Aquifer), but some crops can be grown without supplemental water during wetter years. Moving westward into more arid regions, grasses generally become shorter and more sparse. In eastern portions of the Missouri basin, the climate is humid continental and the vegetation is medium-height bluestem grasses, with mixed oak and hickory forest. The basin’s western rivers, such as the Marias and the Yellowstone, gain a large portion of their flow from spring snowmelt. Throughout the basin, most rain falls during the spring and summer. Much of the basin is characterized by the cold winters and hot summers associated with a continental climate (drier in the basin’s western portions, more humid in the east). Annual rainfall varies from 8 inches in the foothills of the Rockies to over 40 inches in parts of Missouri and Iowa. In the basin’s eastern third, the plains give way to upland plateaus and gently rolling till plains. From there to the basin’s southern boundary lie the Great Plains, with their characteristic widely-spaced streams and broad, flat valleys. The region between the Missouri River (on the north) and the South Dakota-Nebraska border (on the south) is arid and has eroded to form deep valleys. The basin’s northern landscapes include level to gently rolling plains and hills composed largely of glacial till. FIGURE 2.1 Missouri River basin landforms. ![]()
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