From Bulbapedia, the community-driven Pokémon encyclopedia.
Mt. Cleft (Japanese: きりたったやま Steep Mountain) is a Friend Area is Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team that can be obtained by either buying it from Wigglytuff for 5,000 Poké or if Charmander is chosen as the player character or the player's partner. It is in the Mountain Range area, and has a capacity of nine Pokémon.
Mt. Cleft is on a pillar with a small bridge. The terrain is rocky and it has several small indents (craters) in the ground.
This area, deep among the craggy mountains, is a gathering spot for physically tough Pokémon.