I did use a Hoya circular polarizer. The sky was very blue anyway but not that intense. I increased the red in the color balance a little to bring out the redrock a little more. I overdid it some and ended up with a slight purple color to the sky. I liked the effect though and left it.
Occasionally in the higher altitudes here, you can look up through a hole in the clouds and see sky that is just as intensely blue as this picture.