I thought it was a lava field of sorts, too. If it's meant to be fog, try taking a low opacity fuzzy red brush to the whole area to make a less dense misty/cloudy/foggy appearance... leave some of the tallest rock peaks clear of it and lower ones with just a bit to obscure them. And make that fog a bit brighter (more reflective) than the stuff closer to the ground. It may not work out, but could be worth a shot anyway. Looks like liquid right now.

It's a beautiful map so far. Love the color scheme, and the details. What do you have in mind for it when it's finished?