During the last Ice Age, Teesdale was filled with glacial ice hundreds of metres thick which ground up the explosed rocks and smeared the resulting depric down the valley sides and valley bottom. This ice has shaped the landscape today.
Mountain Avens (Dryas octopetela): T Gledhill
When the climate warmed up about 12,000 year ago and the ice retreated, it left a barren landscape of bare and crushed rock. This was rapidly colonised by light-loving plants which thrived in the open landscape of Upper Teesdale. Many of these are now extremely rare plans in Britain but still survive in special places in Teeside where they have remained for nearly twelve thousand years.
Distinctive lozenge-shaped mounds of crushed rock we call drumlins are a particularly characteristic feature of the valley floor, and their deep fertile soils were used for arable cultivation as far up the dale as Holwick in the late Iron Age and the Medieval period. After the Black Death in the mid 14th century, most arable cultivation was converted to pasture and meadow, and Upper Teesdale is now home to some of the most species-rich hay meadow in the country. The North Pennines are home to 40% of such hay meadows remaining in Britain.
Holwick drumlins with a covering of hay meadows: M Rogers