[1] The park covers 8,900 hectares (22,000 acres) in the headwaters of Te Awa Kairangi / Hutt River at the southern end of the Tararua Range.

Hilltops are extremely exposed to the north-west and the south, with high winds and fog.

There can be sudden weather changes, and rivers and streams can rise very rapidly in heavy rain.

The valley floor includes podocarpaceae, alpine tussock and sub-alpine sphagnum bog.

It includes some of the Wellington Region's southern rātā, and native forest birds like kākā, kākāriki and kārearea.