The caves are hewn out of the volcanic basaltic formation of Maharasthra, known as Deccan Trap, the term trap being of Scandinavian origin representing the step like formation of the volcanic deposits. The rock formation, on weathering has given rise to the appearance of terraces with flat summits. At Ellora, one can also have a glimpse of the channels (near Cave 32) through which the volcanic lava once flowed. These channels, due to overheating, have a characteristic brownish red colour. Similar rock was used in the construction of the Grishneshwar Temple nearby and also utilised for the flooring of the pathways at Bibi ka Maqbara.
The hills in which the caves are hewn, forms part of the Sahyadri ranges of the Deccan and dated to the Cretaceous era of the Geological time scale (about 65 million years ago). The hills rise abruptly from the surrounding plains on the south and west, the western surface being extensively utilised for hewing the cave complexes. The hill also supports several streams, the prominent among them being the Elaganga, which drains into the Shiv, a stream of the Godavari river system. The Elaganga is in its full vigour during the monsoon, when the overflowing waters of a barrage in the upstream near Mahismati allows the gushing waters to land at