 During the early 19th century , at the height of the fur trade , steamboats and keelboats began traveling nearly the whole length of the Missouri from Montana 's rugged Missouri Breaks to the mouth , carrying beaver and buffalo furs to and from the areas that the trappers frequented . This resulted in the development of the Missouri River mackinaw , which specialized in carrying furs . Since these boats could only travel downriver , they were dismantled and sold for lumber upon their arrival at St. Louis . 
 During the early 19th century , at the height of the fur trade , steamboats and keelboats began traveling nearly the whole length of the Missouri from Montana <a href='null_genetive' title='1'><mark>'s</mark></a>rugged Missouri Breaks to the mouth , carrying beaver and buffalo furs to and from the areas <a href='null_relcl' title='2'><mark>that</mark></a>the trappers frequented . This resulted in the development of the Missouri River mackinaw , which specialized in carrying furs . Since these boats could only travel downriver , they <a href='uninflect' title='3'><mark>were</mark></a> dismantled and sold for lumber upon their arrival at St. Louis . 
Durin da early 19th century , at the height of tdafur trade , steamboats and keelboats began traveling nearly the whole length of the Missouri from Montana  rugged Missouri Breaks to thdaouth , carrying beaver and buffalo furs to and from the areas the trappers frequented . dis resulted in the development of the Missouri River mackinaw , which specialized in carrying furs . Since these boats could only travel downriver , they was dismantled and sold fa lumber upon their arrival at St. Louis .