How Hill, near Downholme appears as an isolated green island on the landscape. However, not only was it a site of a large univallate hillfort during the later Bronze Age and Iron Age at the entrance to Swaledale but it clearly shows the effects of the last Ice Age on the reorganisation of the drainage of the River Swale. Pre-glaciation, the valley of the proto-Swale carved through the soft rocks to the south of How Hill, but during the last Ice Age this was blocked with ice and moraine, so the glacial meltwaters of the River Swale began to cut to the north of How Hill, in their present day position.
How Hill, an isolated hill illustrating the change in drainage pattern of the River Swale.
A Lidar image of How Hill, clearly illustrating the position of the modern River Swale after it was shifted laterally by glacial actions.