I saw a TV special on geological formations and saw one shot that really got my attention. I took a sorry screen grab of it, and then re-created my own version in TGTP.
Here are the results...
You're getting there! Maybe an overall redder tone in the TG version would help it imitate the image more ;). I would also recommend actually reducing the roughness of the clouds a bit and making sure that you have "Whispy" checked.
The stone colour needs to be a lot closer to the ground colour too.
I agree with what they (up there) said. ;D But, I think yours will easily and eventually look better than the TV version.
Oh, and make the sky a stronger blue.