Ok this shows my ignorance but what do you do to sculpt the rock looking texture and rock wall faces that I see some people use on their mountains and valleys?
There are many different techniques, but some of the most common are using plaster/hydrocal castings, carving plaster/hydrocal, shaping and painting the foam, or buying pre-made flexible foam rock faces. There are pros and cons to each, and most modelers end up using a combination of several methods to achieve a realistic mix or model different types of rocks for different areas on the layout.
Try a small sample project with each method the guys described above, then you'll know which one works best for you...
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