The Wither Hills run between the Dashwood and Taylor passes and are situated directly to the south of Blenheim. Formed by tectonic movement, the underlying rocks are gravel conglomerates and wind blown Wairau loess greywacke. They are named after C.B.Withers who took up a sheep run on them in 1848.
In pre-colonial times the hills were extensively covered in manuka, kanuka and totora forest supporting a large population of moa and other bird species. The arrival of fire with Polynesian explorers resulted in large fires raging across most of eastern Marlborough in the tinder dry conditions. After this deforestation a tall tussock grassland established, building a layer of humus and sustaining the loess of which much of the hills are made.
On European settlement the hills were once again burnt and sown with exotic grasses more palatable to sheep. This started a long period of erosion which scoured out long underground tunnels and left scars visible for some distance. After World War 2 a soil conservation project was begun at the western end through extensive tree planting and improved stock management.
During the summer, the grassy hills usually dry off given them their characteristic golden brown colour. In winter higher rainfall and cooler conditions tends to green the hills with fresh grass growth.
Although the hills are mostly bare grassland, there are the occasional stand of introduced pine trees, and in the bottom of valleys a mixture of indigenous and exotic vegetation.
On December 26, 2000, a devastating fire swept through the Wither Hills, destroying farmland, and much of the efforts at reforestation. Some estimates suggested that it would take at least ten years to recover from the damage.
The Marlborough District Council owns and manages much of the Wither Hills as a working farm and recreational park and have constructed a network of recreational walking and cycle tracks and implemented a conservation and restoration programme for the remaining bush remnants.
Extensive planting of native species has been done from the Redwood Street entrance to the farm park up the Sutherland Stream catchment. Species include harakeke (flax), hebes, lancewoods, coprosmas, cabbage trees, manuka and Marlborough's iconic rock daisy (Pachystegia insignis) among others.
Extensive exotic planting has occured further west around Quail Stream with various Pinus species, walnuts, accacias, willows, tree lucerne, eucalypts, oaks among the vegetation present.
The western end of the hills along Taylor Pass Road, has a car park and entrance to the park and walking track to the Rotary Lookout. Further south along Taylor Pass Road is an entrance to a section of the park dedicated to mountain biking with tracks of various grades from relatively modest gradient passing through exotic forest to steeper, more technical tracks on the open hillside.
A section of the western end of the Wither Hills off Taylor Pass Road also is the site of the Blue Gums landfill which provides a location for burial of household and industrial waste from Blenheim. Access to the site is restricted to the public. The council operates a roadside collection and transfer station for members of the public to dispose of waste.