Geo-Mod was developed by Volition as a part of the development for the first Red Faction game. Geo-Mod allowed players to use explosives to destroy their in-game environment, provided that it was dirt or concrete. Even if you decided to tunnel into a mountain you would always run into indestructible surfaces that no rocket or demolition pack could break for. Even in games today, no developer has fully managed to properly deliver on what Geo-Mod attempted to do.
Geo-Mod in the first game of the series featured deformation of natural terrain and cavern walls, with limited building deformation. The latest in the series, Red Faction: Guerrilla, departs from this, featuring more detailed building destruction whilst forgoing terrain deformation.