The most significant ranges in this area are the Spenser Mountains, with their extensions to the north-east in Nelson Lakes National Park (Ella, Travers, St Arnaud Ranges), and further east with the Raglan Range. These mountains are young and, like the rest of the Southern Alps, rise sharply east of the Alpine Fault, which is traced here on the northern border of Nelson Lakes National Park and in the Wairau Valley. The rate of uplift and level of precipitation, and consequently also the rate of erosion, are markedly lower than further west in the axial zone.

Four factors combine in these mountains to generate a marked sense of uniformity, especially in the Spencer and Nelson Lakes National Park mountains:

- rock type is almost uniformly greywacke,
- similarity of altitude of summits and crests,
typically 2200-2300 m (7218-7546'), - deep U-shaped valleys and widespread glacial landforms,
- north-south to north-northeast-south-south-west orientation of most valleys.

The beech forests which extensively cover valley floors and mountain slopes add to this uniformity. All four species of southern beech (Nothofagus) are present. The treeline makes a particularly striking feature in the landscape, extending in a straight and even line, as if artificially drawn, along mountain sides at about 1400 m (4593').