 With more than 170 @,@ 000 square miles ( 440 @,@ 000 km2 ) under the <unk> , the Missouri River watershed includes roughly one @-@ fourth of all the agricultural land in the United States , providing more than a third of the country 's wheat , flax , barley and oats . However , only 11 @,@ 000 square miles ( 28 @,@ 000 km2 ) of farmland in the basin is irrigated . A further 281 @,@ 000 square miles ( 730 @,@ 000 km2 ) of the basin is devoted to the raising of livestock , mainly cattle . Forested areas of the watershed , mostly second @-@ growth , total about 43 @,@ 700 square miles ( 113 @,@ 000 km2 ) . Urban areas , on the other hand , comprise less than 13 @,@ 000 square miles ( 34 @,@ 000 km2 ) of land . Most built @-@ up areas are located along the main stem and a few major tributaries , including the Platte and Yellowstone Rivers . 
