Sandy bits.
Wash and drybrush will give it lots of depth. (dark red brown wash with a sandy brown drybrush for a clay dessert, change the colors up to suit you.)
About the sand color, on my latest diorama (http://www.coolminiornot.com/258482) I used a mix of kommando kaki, desert yellow and a bit of snakebite leather, drybrushed with kommando kaki and ivory (vallejo) and finally I've added some sand colored pigments to make it more dusty.