Yup, tried again and it doesn't let me cast the spell. I have the brownish square where I want to target. I can raise and lower and create a mountain, but not blistering sands.

Stupid forests are impeding the growth of a couple of key cities and I am losing a influence war with two neighbors. I am glad there is no city fliping ala Civ, but sheesh, I am losing resources and can't leave the areas because I am sorrounded.