Feanaaro is right. Here is a quick example of how this might work:

(i) Make two new layers above your map layers, calling one 'slope shadows' and the second one 'slope highlights'. It does not matter which is above the other.
(ii) On 'Slope Shadows' Draw a black line with a crisp unfuzzy brush along the top break of slope between grass and stone. Now use the blur tool to blur the bottom of this black line only into the rock. I did it very badly in the example below - yours should be crisper and thinner along the top and better blended along the bottom.
(iii) Change to highlight layer; now get a hugely thick white fuzzy brush and paint with abandon above and below your black line, aiming to get the upper half of the rock texture covered in white. Use blur to even it all out.
Your map should now look like this, but obviously much better because you were more careful.
Click image for larger version.  Name: Hill Campsite_1_small2.jpg  Views: 487  Size: 764.0 KB  ID: 55417
(iv) turn both layers to overlay mode and duplicate the shadow slope layer. Your map should now look a bit more 3D and your rock should 'sit' down in your grass - hopefully!
Click image for larger version.  Name: Hill Campsite_1_small.jpg  Views: 378  Size: 808.9 KB  ID: 55418
By the way you can easily upload your full map if you export to .jpg 85% compression rather than .png., with no visible loss of quality (there is a loss of quality however it is imperceptible to the human eye on a computer screen so its ideal for uploading to CG). Your boulders in the top-centre of the map are really good by the way.