From Bulbapedia, the community-driven Pokémon encyclopedia.
Camerupt Mountain is an anime-exclusive location. According to the anime, it is situated near a river by Valley town. At the summit is an open area where people can enjoy stargazing. In the anime, Ash and his friends scale Camerupt Mountain to help a Lunatone being chased by both Team Rocket and the Pokémon Mystery Club. When both Team Rocket and PMC out of the way, Lunatone was able to catch some moonlight to regain its energy and fly back into space.