The Olivine eco-region on the West Coast consists of two districts with extreme rainfall and rugged, glacier-carved terrain. The Cascade district is defined by its ultramafic mountains and moraine plateaus, where infertile soils support stunted forests and barrens. The Pyke district is a geologically diverse area of wet, forested ranges and large swampy lowlands, featuring a unique mix of beech forests and stunted mountain beech on old moraine. Both districts are critical habitats for native birds like the kākā and Fiordland crested penguin.