Excellent and concise. That almost exactly the way I do my terrain too. You should check out cgtextures.com for some excellent textures to look at to get these kind of canyons and water. One of the things I have noticed about rocks is that they appear almost exactly correct at any scale. I.e. you can take a small bit of dirt and scale it up and it looks exactly as though it was a hundred foot high bit of rock. You cant do that with water so well but getting shots of water is not so hard. I have found trees the hardest being big and not something that you can cheat on very well. I'll rep if I am able.

Edit -- Nope hah. Been dishing it out to you already it seems !