How would i model a canyon?

How would i model a canyon? like this ( a Full canyon for animation) http://images.travelpod.com/users/muzz_travelling/argentina_2005.1145812860.llamas.jpg

Start in top view with a grid, or a plane with a lot of subdivisions. This is ground level. In the image you have hills and mountains, so select some vertices near the peaks of the hills and mountains, switch to side view, turn on proportional editing [o] and then grab and move in the z direction. The peaks will go up, and proportional editing will pull surrounding vertices up with them. Experiment with the strength of the proportional editing [mouse wheel increases or decreases the size of proportional editing’s circle of influence], and put a camera in the scene so you can see what it looks like from “ground” level.

You might also experiment with moving the peaks up only a little bit, then selecting more near the peaks, and moving up another little bit, and so on.

Model the erosion in the mountains by selecting a row of vertices going down the side of the mountain, and moving them down (use less influence in the proportional editing when you do this or you just bring down the mountain you just brought up.)

Tweak until finished. Since you’re planning on animating, decide where the camera will look and make sure the model looks good from those directions. Make it look good a bit past that too, to give yourself some extra wiggle room. Don’t spend a lot of time tweaking places the camera won’t see.