Symbolism, Imagery, Allegory
Nature imagery is huge in this book. That's why Inman is carrying Bartram's Travels, a book about wandering and nature. It's also why we get so many descriptions of weather, plants, animals, and forests. They set the mood, symbolize what the characters are experiencing psychologically, and serve as ways of exploring the nature of the world and the people in it.
One example is the point where Ada notices a small detail about a creek and thinks about how that detail might be a metaphor for human life:
Where it ran shallower and slower, then, were the places prone to freezing. Monroe would have made a lesson of such a thing, Ada thought. He would have said what the match of that creek's parts would be in a person's life, what God intended it to be the type of. (16.51)
Things that are true in nature may be true in another way in human life, at least in the highly symbolic world of Cold Mountain.
If Inman's opening Bartram's Travels, there's probably a symbol coming. If it's raining, there might be a reason. Ranger Rick has nothing on Frazier: nature means a lot in Cold Mountain.