Here’s a nice photo tutorial on modeling desert wadis.
Modeling California Desert Bases
The tips in this video for modeling California Desert bases also could be applied to making various bits of terrain. I have some friends who are currently painting up a Zorro game …
Desert Mesa Modeling
How to make a Desert Mesa for your miniature wargames.
Making A Desert / Wasteland Terrain Cloth
The 1000 Foot General has a tutorial on making a desert / wasteland terrain cloth.