Hi 3D outlaw.
There are several ways in Carrara to create simple rock shapes,. such as the Metaball modeller, or the Vertex modeller has an option to Construct / Organic , to take a simple flat shape and make it 3D. (See pics)
If you add a couple of Morphs to that organic object, then you can Duplicate, and change the shape of your rocks, then add those to a surface replicator to apply them to an surface like a terrain.
You can use the options in the Surface Replicator, to rotate and scale them differently.
You can also use the “Create Real” option, to generate real objects instead of replicated.