The color is strong at this time of year, as the rocks still have winter moisture in them, and that really helps them show a strong red cast. (Basically oxidation)
As the spring moves into summer they dry out, and the color fades quite a lot.
Also, have found with experience that the rock surface reflects a lot of light, and using the CPL takes that sheen away giving a deeper color. Couldn't believe it the first time I tried it, but I guess the rock face acts as a kind of low grade reflector, polarizing the light as it bounces off towards the camera.