From the Setting Guide
The region now known as the Howling Badlands was once the Eltraeth Dominion, an Elven forest nation.
War with the Cinder Dwarves resulted in a cataclysmic explosion which covered the entire region in a magical radiation which dyed the sands red.
The red desert gets its moniker from the voices that carry on the night air; terrible screams that some claim to be the souls of those killed during the great war still clinging to the material plane.
Despite the long-term health effects of cinder exposure, the badlands are a popular destination for those wishing to harness the latent magic in the region, either through harvesting cinder, or by capturing the power of the magical lightning that occurs across the region.