Hi Tom, I agree with Ryan. Great sky, but we need to see more of it. It's amazing that you were able to get such a dark sky with only a yellow filter! In my part of the country I'd need IR plus a red filter! Real nice shot.
I think I would have raised the camera so the bottom of the image touched the bottom of the second large rock from the left. This gives you the extra 1/2 inch of dramatic sky and eliminates the plain sand.
That said...I do very much appreciate the subject and the overall treatment is great.