The Rahim Wastes is a large, varied desert that stretches from north to south for hundreds of miles to the east of the Skulls. To its north it borders the Wuthering Wights; to its west, the Skulls; to the east, World's End; and to the south, the Krachi Lowlands. The Wastes are comprised of three distinct parts 1) the Burning Sands 2) the Gods' Staircase and 3) the Rahim River basin.
The Burning Sands
The Burning Sands is the largest part of the Rahim Wastes. It extends from the Krachi Lowlands in the south all the way up to the beginning of the Rahim River basin in the north. The Burning sands is a low elevation basin filled with shifting sand dunes and sand-scoured, half buried outsider ruins. A few small rivers fed by meltwater from the Skulls means that some creatures can eke out an existence in what has been called by some explorers "the frying pan of Morgrave". Few kith have ventured far into the Burning Sands, almost all prefer to bypass it using existing routes along the Gods' Staircase if some business requires them to traverse the desert.
The Gods' Staircase
The Gods' Staircase is a high desert steppe bordering a majority of the Rahim Wastes' shared border with the Skulls, excepting the southern portion of the Wastes, which is a continuation of the Burning Sands. The Gods' Staircase is named after a relatively small area within the region we call "the Gods' Staircase": a series of concentric cliffs that look like the staircase that the gods would use to climb to Gods' Rest, the tallest mountain in the skulls and the supposed home of the gods.
The Gods' Staircase is high desert and more vegetation and animals can survive here than in the Burning Sands. In the south, it's a hot desert, like the Burning Sands, but around the Rahim River basin it transitions into cold desert.
Rahim River Basin
The Rahim River is the main source of life in the Rahim Wastes, and the namesake of the entire desert. Here, plants and creatures can thrive in the wide floodplains of the valley. The river is fed by meltwater from the Skulls, which pools in an alpine valley before making its way through the desert to the coast. This valley in the mountains is the secret to the Rahim's volume of water - all the meltwater flows to one place before become the wide Rahim River.
The basin is also seen as the transition between hot desert to the south and cold desert to the north. Although the transitionary area is much broader than the river basin, this is a useful shorthand for adventurers.