I'm also not clear about what you're looking for.

There are lots of threads with brushes for creating mountain ranges, and there are threads with tutorials for creating mountain range effects. (I would also argue there are plenty of PS-oriented tutorials.)

By geography do you mean information about how forests, mountains, etc. would realistically be arranged on a continent? Or how they affect the placement of cities and roads?

I'm not trying to be contrary, I'm just wondering if you could more clearly describe what you're after. It seems like mountain and river (especially mountain) resources abound if you just flip through the Tutorial/How-To forum. Use Ctrl-F to quickly jump down the page to keywords like mountain or river.