In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

One dam on this river is located where the Spokane Hills meet the Big Bend Mountains. Along with Canyon Ferry Dam, Garrison Dam on this river forms Lake Sakakawea. This river is formed by three headwater tributaries which meet near a town in Gallatin County; those tributaries form this river in Three Forks, Montana. Besides the Madison and Jefferson Rivers, other tributaries of this river include the Platte and Yellowstone Rivers. This river flows through the Dakotas before forming part of the border between the namesake state and Kansas. For 10 points, name this river which joins with the Mississippi River near St. Louis.
Social Science