Formed just south of the village of Copley, by the confluence of Arn Gill (to the south, coming west from south of Langleydale Common) and Hindon Beck (to the north and coming east from Langleydale Common), the Gaunless wends its way east, passing the settlements of Butterknowle, Cockfield and Evenwood and through West Auckland before skirting the south and east of Bishop Auckland on its way to meet the River Wear.
An extension of the Copley Met.Office weather station has been placed at the head of the river at Copley Lead Mill to study its unique climate of frost and snow. It lies in a frost hollow and receives no sunshine between October and March because of its geography.
