Ugh like a dummy I posted a screen shot with my custom version of a mib color mix lol, but yeah I'd use the color mix to layer my textures. I would shuffle on over to Mudbox to sculpt the terrain and paint some base textures and a set of rocks so I could paint those around the bank in Maya. Making a set of odd twigs/ fallen branches would be cool too. Another thing, it wouldn't be a bad idea to take that river into Mudbox as well and try to get some ripples that flow with the form instead of being so procedural looking.