Perhaps others were confused, as I was, about the nature of your question. I think you are asking about a graduated neutral density effect, which changes the relative exposure values in different parts of the image, instead of a neutral density filter, which affects the exposure of the overall image. The Arizona shot has an extremely strong horizontal shadow which dominates the viewer's experience of the scene. The graduated ND effect you applied has softened the shadow effect somewhat but the shadow is still quite overwhelming to me. The best thing you can do with this image is to bring more attention into the lower left foreground by brightening and warming it somewhat more. But, for me, the shadow in the canyon is just too strong. This is a shot that needs different light.