So, if you look in the primary LAM material (Landscape_Automaterial_M) you should be able to search around and find the foliage comment box (that’s where this screenshot is taken). If you select the “Grass” node, you can see where each of the grass types are defined. If you look in those, you’ll be able to hunt down the location of the rocks being included in one of the types.
Lemme know if this isn’t helpful.
hugs,
trent