It is managed by Hampshire and Isle of Wight Wildlife Trust, and topped by an Iron Age hillfort, a scheduled monument.

The local ecology is dominated by the chalk, which results in a thin dark soil, a rendzina, which favours lime-loving plants from orchids to bellflowers.

[3] The fortifications consist of a single rampart (univallate dump or glacis) with an outer ditch, begun in the Early Iron Age; much of the way around there is also a counterscarp bank.

[4] The site was occupied until the Middle Ages, as demonstrated by archaeological finds such as Iron Age pottery, a saddle quern, objects of worked bronze, iron, bone, and stone, as well as whetstones, spindle whorls, and remains of bones of sheep/goat, shorthorn oxen, horses, pigs, red deer, and dogs.

St. Catherine's Hill belongs to the roughly 90 million years old Upper Cretaceous 'New Pit Chalk Formation' within the Turonian stage.

[13][14] The soil on the hill is a thin dark rendzina, directly on top of the chalk; it is thinnest high on the slopes, thickening into the valleys.

This provides a varied set of local environments supporting a range of communities of flowering plants, including small populations of numerous downland species of orchids.

Where grazing has kept the grass short, the grassland is dominated by sheep's fescue grass, accompanied by lime-loving (calcicolous) plants such as common rock-rose, salad burnet, thyme, horseshoe vetch, kidney vetch, fairy flax, clustered bellflower, and orchids such as autumn lady's tresses and frog orchid.

A feature of the plant community is the presence of forbs of relatively wet grassland, such as saw-wort, hemp agrimony, and devilsbit scabious.