Summerhill Force is a waterfall on Bow Lee Beck in Teesdale, County Durham, reached via a short walk from the Bowlees Visitor Centre. The path follows the beck through woodland, passing small cascades and pools before arriving at the main fall.

At the waterfall, Bow Lee Beck plunges over a thick layer of grey limestone — known historically as the Five Yard Limestone — beneath which softer sandstone and dark shale create a distinctive layered face.

Because the lower rock types erode faster than the limestone above, the waterfall has developed a pronounced overhang, forming the sheltered recess known as Gibson's Cave.

This undercutting process continues today, slowly moving the falls upstream and deepening the gorge. The rock layers date back roughly 330 million years, formed in ancient tropical seas and river deltas.