Skull Valley is a location just outside of Mount Paozu which was seen in the second episode of Dragon Ball, "The Emperor's Quest" and in Chapter 2 of the Manga. Goku and Bulma camp out there for the night on the first day of their journey to collect the Dragon Balls. The land is very normal but another part of it is a canyon full of bones and populated with carnivorous wolves. Emperor Pilaf's minions Shu and Mai investigated a glow coming from the valley thinking it was a Dragon Ball. From Dragon Ball Wiki, a Wikia wiki.