Here you can find several cliff high quality models and example how to gather landscape using this models.
Triangles count:
Huge stone 1 - 6000 tris
Huge stone 2 - 4990 tris
Big stone - 5000 tris
Flat stone 1 - 2000 tris
Flat stone 2 - 5830 tris
Flat stone 3 - 3990 tris
Mid stone 1 - 4000 tris
Mid stone 2 - 960 tris
Small stones (for all 5 meshes) - 7018 tris