Stained Caverns

Those who were killed in the Erasure of Depravity did not become a mountain of corpses. The remnants of civilization would not have had the means to dispose of them, and would have been ousted from all major cities. Instead, the victims shattered into tiny crystal fragments, colored in accordance with the Warden who slayed them.
These crystal fragments sifted through the earth over many years, and eventually settled in caverns underneath. To this day, one can tell which warden killed the most people in an area based on the color of the caverns. They earned the title Stained Caverns once people realized the origin of their brilliance.