The West Nelson Mountains are considered to include the ranges lying north of the Buller River and west of the Moutere depression in the north-west corner of the South Island. Unlike most other parts of New Zealand, there is no well-defined axial range, but rather a group of mountain ranges of similar altitude and form separated by fast-flowing rivers deeply entrenched in mountain gorges. The largest mountain group–the Tasman Mountain–lies between the Aorere and Karamea Rivers and extends across to the West Coast. The highest peak is Aorere (5,604 ft) at the head of the Aorere River. Lying west of these mountains are a series of smaller ranges fronting the Takaka-upper Karamea depression and separated by major east-flowing rivers draining towards this depression. These are, from south to the north–the Peel, Lockett, Snowden, Douglas, Devil, Anatoki, and Haupiri Ranges. The highest peak is Devil River Peak (5,823 ft) in the Devil Range. East of the Takaka – upper Karamea depression lies the north-east-trending Pikikiruna and Arthur Ranges overlooking Tasman Bay, and the Moutere depression on the east, rising to 5,990 ft in the Twins. South of the upper Karamea and Wangapeka Valleys are the north-trending Glasgow, Lyell, Owen, Lookout, and Hope Ranges, separated by major tributaries of the Buller River and rising to 6,155 ft in Mount Owen. The Wakamarama and Iwituroa Ranges lie north-west of the Aorere-Heaphy depression extending to the coast.

The West Nelson mountains are a series of block-faulted and block-folded mountain ranges composed of ancient Paleozoic sedimentary, metamorphic, and granitic rocks of extremely complex structure. The Paleozoic rocks are flanked by and overlain by softer Tertiary sedimentary rocks, largely eroded from the mountain ranges but preserved in the down-faulted depressions. The smooth, plateau-like summits common in these mountains are preserved remnants of the early Tertiary land surface, partly modified by marine erosion, that was buried below the Tertiary sediments. Most of the region is forest covered, with settlement and farming activities confined to the lowlands and coastal flats and terraces. Although there are no permanent snow-fields or glaciers, the ranges are snow covered in the winter and spring months to below 4,000 ft. A power station in the middle Cobb Valley has an installed capacity of 32,000 kW and is fed by water piped through a mountain ridge from an artificial lake in the upper Cobb Valley.

by George William Grindley, M.SC., New Zealand Geological Survey, Lower Hutt.