High Clear Down is one of the more remote nature reserves in Wiltshire, over one mile from a main road, reached by an unpaved track that needs a high clearance vehicle to negotiate. The reserve contains a relatively small (24 acre) area of chalk downland, steep in places, and facing southwest, looking across a shallow valley; it is home to a good range of wildflowers including at least six types of orchid - common spotted, pyramidal, fragrant, green-winged, frog and autumn lady's-tresses, the first three of which are widespread - plus abundant, blue-flowered chalk milkwort and, the rarest plant, early gentian (blooming in May and June), the presence of which was the main reason for creation of the reserve, in 1998.
Dense clumps of hawthorn extend across the upper edge of the reserve, on top of a ridge, and smaller bushes are scattered across the slopes below, but most of the land is covered only by short grass, making it quite easy to spot wildflowers, and butterflies, of which over a dozen species have been recorded. Because of the out-of-the-way location, the reserve is infrequently visited and is not within sight of any building so has a peaceful, remote ambience. The abundance of wildflowers is due in part to the steepness of the land and the poor quality soil, making the land impractical for crop growing, and because the grassland has not been subject to fertilisers and pesticides, used only for occasional livestock grazing.
The nature reserve lies west of the B4192, north of Aldbourne. The suggested approach is along a narrow byway, much of which has a higher centreline, starting half a mile outside town, opposite a barn, soon bearing left at junction and continuing alongside fields for 1.2 miles, past the fenced-off ruin of an abandoned farm (Lodge Lower Barn) and on a little further to the reserve entrance, at the southeast corner. The ruin is a good place to park if driving, though Wiltshire Wildlife Trust suggest that most people walk all way from the main road. There is a shorter access route from the north, starting at the settlement of Upper Upham, driving down a better quality track to a junction at the far end of the byway, from where the reserve entrance is 0.7 miles away. In the reserve, the best wildflower area is towards the centre, and across the west-facing slope. Most of the early gentian seems also to be near the centre, about half way up the hillside. Beside the hawthorn along the upper reaches, the only other features are a tiny pond in the northeast corner, and traces of two earthen embankments, associated with an ancient field system, more of which can be seen on top of the ridge.