where does it originate from?
It officially starts at the confluence of the Jefferson and Madison in Missouri Headwaters State Park near Three Forks, Montana.
Missouri River
The Missouri River officially starts at the confluence of the Jefferson and Madison in Missouri Headwaters State Park near Three Forks, Montana, and is joined by the Gallatin a mile (1.6 km) downstream.
what river forms the border between iowa and nebraska UNANSWERABLE which are the main tributaries of the missouri river? James, Big Sioux, Grand River systems etc.
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Missouri River [SEP] Course
It slows into the Lake Oahe reservoir just before the Cannonball River confluence. While it continues south, eventually reaching Oahe Dam in South Dakota, the Grand, Moreau and Cheyenne Rivers all join the Missouri from the west.