Here you can find a lot of blocked rock meshes which you can use in any your landscapes.
Triangle counts:
Blocked rock M 1 - 9800 tris
Blocked rock M 2 - 8000 tris
Blocked rock M 3 - 6300 tris
Blocked rock M 4 - 3370 tris
Blocked rock M 5 - 2990 tris
Blocked rock M 6 - 6800 tris
Blocked rock gathered 1 - 16600 tris
Blocked rock gathered 2 - 12500 tris
Blocked rock gathered 3 - 27000 tris
Blocked rock gathered 4 - 6500 tris
Blocked rock gathered 5 - 22650 tris
Blocked rock gathered 6 - 12570 tris
Blocked rock gathered 7 - 8280 tris
Blocked rock gathered 8 - 10500 tris
Blocked rock gathered 9 - 10400 tris
Blocked rock gathered 10 - 5590 tris
Blocked rock small 1 - 2600 tris
Blocked rock small 2 - 2390 tris
Blocked rock small 3 - 2140 tris
Blocked rock small 4 - 2050 tris
Blocked rock small 5 - 1760 tris