The top of a rock - The blood was poured upon a naked, dry, rock where it could not be absorbed or unnoticed.
Related Commentaries of Ezekiel 24:7
Ezekiel 24:7-8
7 For her blood is in the midst of her; she set it upon the top of a rock; she poured it not upon the ground, to cover it with dust;
8 That it might cause fury to come up to take vengeance; I have set her blood upon the top of a rock, that it should not be covered.