 The beck runs from its source on Burnt Horse through the valley between Lonscale Fell and Blencathra to its confluence with the River Greta at Brundholme near Threlkeld.Although the top of the stream from Burnt Horse is widely cited as the source of the Glenderaterra, the Royal Geographical Society and other authorities state that the source of a river is the furthest point from its mouth or confluence with the river it meets downstream, "regardless of names attached to the contributing flows.