I took your color image and had a go at it, in hopes of being helpful The first pic is the final result.
1. First I added a simple gradient (second pic) set to overlay at 50% opacity.
2. Second I blurred everything on the original that was at the bottom of the slope, in this pic the bottom is on the right side (third pic). I used the blur tool at about 45 pixels for the tip of the brush.
3. Next I added a layer of 50% gray, set it to overlay then using the dodge and burn tools (at various tip sizes) I created some relief to give it some extra punch (fourth pic).
The black in the gradient might be a bit too much but I thought that yours was too light...you're on the right track, though, so keep up the good work.