Really nice atmosphere. At this stage of work, I'd turn off the clouds, and concentrate on getting better variation in you grass and rocks, as well as your rock texture, to really bring this scene to life.
Possibles.
Break up the grass to create clumps of grassy areas, revealling some earth perhaps.
Use a PF to create gaps in your rock population. Add another two sizes of rocks, and use the same PF to blend, but use colour adjust shaders to create smaller white area masks for incrementing sizes in stones. Largest being rarer, smaller more frequent.
The rock texture needs some dialing back on the reflectivity and brightness. Maybe try using a low contrast PF to blend the reflectivity to get some matt areas. Maybe some dirty parts in the texture too, but that's subjective.
You can really add a lot to this scene with not too much work, because your fog is telling the story.
