Valley in southwestern Montana between the Bitterroot Mountains and the Sapphire Mountains, the Bitteroot River flows through it.
The valley stretches from Missoula, MT where the northward flowing Bitterroot flows into the Clark Fork of the Columbia River to the south, where the Bitterroot and Sapphire ranges gradually coalasce together. The Western and Eastern borders are more clearly defined, since the ranges that bound it are very well defined. Unlike some valleys (such as the Willamette Valley) where you can only tell you are in valley on an exceedingly clear day, The Bitterroot and Sapphire ranges, being only around 15 to 25 kilometers apart, let you know that you are in a valley.
The Valley has some interesting properties. The first of these is perhaps that despite the fact that the valley is in the extreme rainshadow of the Bitterroot range, and averages not more then two dozen centimeters of rain per annum, it is rather lush and well supplied with waterways and marshes. This is due to the fact that the surrounding mountains have a rather massive snowpack that melts slowly, providing the valley with water throughout the hot dry summer months.
The river itself follows a fairly predictable course for a river of its size: it starts out in two forks in the mountains, goes through a process of braiding, with many sandbars and oxbows but settles down in the last few miles of its run.
The Valley has a rich assortment of wildlife, although not by Montana standards. Most of the normal herbivores are present and common, and the occasional bear and mountain lion shows up in a fit of confusion.
As for the politics and culture of this area, most of what can be said about the rural West and its combination of poverty, independence, artistry and ignorance can be said about the Bitterroot Valley, only more so. Sure, there are plenty of people here who are members of the NRA, and there are plenty of people here living in converted caboosees, painting folk art. Of course, in the Bitterroot Valley, all of this is played out in one of the most beautiful places I have seen.