The namesake of the duchy, the Dedyre Downs are a cluster of iron-veined hills on the northern edge of the Greenmarsh. Despite not being inhabited by either the Goliath Dominion or the Ssthessic Vrasa that followed it, some of the oldest evidences of civilisation in the Valley of Endon can be found there, in the caves near the town of Rantil.

However, despite the shelter of the caves within the Downs and riddling the Breaklight Cliffs on the southern face of the Downs, the surface of the hills is dry and inhospitable, rocky and sharp. They are the prime territory for many of the most dangerous predators that have been driven from the lowlands, and even some that prey upon humanoid races.