The Valley of Rocks was a region of Skaro. It was so dry that no life could survive more than eight hours without suffering dehydration, and even the rocks were corroded into an almost weightless substance.
Don Morais and Zec, having been captured by the Daleks and forced to find doranium for them, journeyed to the Valley of Rocks in their search. After surviving a landslide and escaping from quicksand, they discovered a cliff made of the substance and a newly-built Dalek space station. After short-circuiting the electric charges in the doranium, Don and Zec escaped back to their ship. (COMIC: The Dalek Trap)