 Beacon Hill is a section of east-facing Upper Chalk escarpment.Both Beacon Hill and Old Winchester Hill have a claim to being the point at which the main north-facing scarp of the South Downs turns northwards around the western end of the Weald; Beacon Hill is lower, but represents a higher level within the chalk, and Old Winchester Hill is cut to the north by the upper Meon valley.Small  suggests that the upper Meon (which like the upper Itchen flows east-west) was originally a headwater of the Itchen following the col to the north of Beacon Hill, before the south-flowing lower Meon cut back through the chalk.