Some guys run paddles in the "silt" around me, there are large fields of basically fine black sand(coal dust/small rocks discarded in mining) that really kill the engine, and also large piles of this that form mini mountains of rock and silt, it is really fun! but it kills your quad to, coal dust is very fine and corrosive, The mud it creates can be very sticky.
Ya, another place that is harder on a machine than sand is the Cinders near Flagstaff AZ. You've got to run paddle tires if you want a chance of making it up some of the big cones, I've only been there once ran the Banshee up chickenshit hill, that machine has never run so hard. Think of the volcanic rock that you put in yor gas grill, size is from dust to golf ball but mostly pea gravel, thing is you can stack it much steeper than sand!
If you can make it to the top you have accomplished something, coming down is the real adventure, the more you try to slow down the more control you lose