If you are unsure if a rock is a disguised golem or not, a spyglass shows their name and level even when disguised. Also, when disguised, the rocks often move slightly as you get close, re settling onto the terrain.
Rock elementals are extremely tough to kill or knockout. Over encumbering them inside or around your base and setting them to aggressive allows them to defend your base with their rock throw attack without being kited away by enemies.
The Rock Elemental is a massive rock monster that is typically found disguised as a stone formation. When a survivor enters its territory, it will begin thrashing and throwing large boulders. Once tamed, it can be a highly effective siege weapon to bring into battle.