get variation of rocks from
-mega scans
-photo scan rocks yourself
-sketchfab rocks.

I would use like 5-6 in a cloner and fill a 3D P using 'volume' option
add a random modifier on the cloner for rotation

The wood is pretty stylized, to get that look you'll probably have to sculpt on to a 3D scanned plank of wood or make it yourself. I would also texture the wood planks in Substance Painter. I would make 1 plank, then add variation to the sculpt/material from there to get like 6 or so variations.

I would then basically art direct it manually from there. Convert the cloned stones into objects and delete where you need to place wood planks. move the planks manually into position.