Fire Mountain (Viz "Fry-Pan Mountain") is a giant mountain ruled by the Ox King that is just outside the Diablo Desert. Along time ago the Ox King had a wizard surround his castle with fire to keep intruders out but got out of control and even he wasn't able to get in. When Goku tries to go into the castle to find the Dragon Ball he fails and the Ox king gets angry at him and fights him. He eventually has Master Roshi come over by sending Goku and Chi-Chi. Master Roshi puts the fire out with the Kamehameha but ends up destroying his castle and the mountain. Afterwards it is then a village ruled by the Ox King and his daughter Chi-Chi. It is seen later various times in the anime as the small village but never again in the Manga.
In the chapter "...And Into the Fire!", Oolong describes a common legend surrounding the mountain, saying, "Once upon a time it was 'Pleasant Mountain,' and it live up to the name. But about 10 years ago, a fire spirit fell form the heavens and transformd it into a mountain of eternal flame... So they say."
Later on in an Anime Filler in the Piccolo Jr. Saga once Goku and Chi-Chi get married and have their wedding at his castle the fire starts back up and Goku and Chi-chi go on a quest to find the Bancho fan to put it out. In conclusion Goku fights the guardian Annin to put the fire out and brings peace to the Ox Kings Village again.